Directory Traversal
Detailed paths
Overview
moment is a lightweight JavaScript date library for parsing, validating, manipulating, and formatting dates.
Affected versions of this package are vulnerable to Directory Traversal in the locale() function, whose locale name validation is circumvented by a non-string value, so an object can direct the load to an attacker-specified path. An attacker can cause a file to be loaded from a path of their choosing by supplying a non-string value that the application passes to moment.locale(). This requires the application to hand user-supplied non-string input directly to moment.locale(), plain strings are unaffected because the existing validation rejects those containing path separators, and only server-side npm consumers are in scope.
Note: This is a bypass of the fix for the vulnerability described in CVE-2022-24785.
Details
A Directory Traversal attack (also known as path traversal) aims to access files and directories that are stored outside the intended folder. By manipulating files with "dot-dot-slash (../)" sequences and its variations, or by using absolute file paths, it may be possible to access arbitrary files and directories stored on file system, including application source code, configuration, and other critical system files.
Directory Traversal vulnerabilities can be generally divided into two types:
- Information Disclosure: Allows the attacker to gain information about the folder structure or read the contents of sensitive files on the system.
st is a module for serving static files on web pages, and contains a vulnerability of this type. In our example, we will serve files from the public route.
If an attacker requests the following URL from our server, it will in turn leak the sensitive private key of the root user.
curl http://localhost:8080/public/%2e%2e/%2e%2e/%2e%2e/%2e%2e/%2e%2e/root/.ssh/id_rsa
Note %2e is the URL encoded version of . (dot).
- Writing arbitrary files: Allows the attacker to create or replace existing files. This type of vulnerability is also known as
Zip-Slip.
One way to achieve this is by using a malicious zip archive that holds path traversal filenames. When each filename in the zip archive gets concatenated to the target extraction folder, without validation, the final path ends up outside of the target folder. If an executable or a configuration file is overwritten with a file containing malicious code, the problem can turn into an arbitrary code execution issue quite easily.
The following is an example of a zip archive with one benign file and one malicious file. Extracting the malicious file will result in traversing out of the target folder, ending up in /root/.ssh/ overwriting the authorized_keys file:
2018-04-15 22:04:29 ..... 19 19 good.txt
2018-04-15 22:04:42 ..... 20 20 ../../../../../../root/.ssh/authorized_keys
Remediation
Upgrade moment to version 2.31.0 or higher.
References
Regular Expression Denial of Service (ReDoS)
Detailed paths
Overview
linkify-it is a Links recognition library with FULL unicode support
Affected versions of this package are vulnerable to Regular Expression Denial of Service (ReDoS) due to quadratic algorithmic complexity in the match function. An attacker can exhaust CPU resources and cause significant delays in processing by submitting specially crafted input containing a large number of email-like or link-like strings.
Details
Denial of Service (DoS) describes a family of attacks, all aimed at making a system inaccessible to its original and legitimate users. There are many types of DoS attacks, ranging from trying to clog the network pipes to the system by generating a large volume of traffic from many machines (a Distributed Denial of Service - DDoS - attack) to sending crafted requests that cause a system to crash or take a disproportional amount of time to process.
The Regular expression Denial of Service (ReDoS) is a type of Denial of Service attack. Regular expressions are incredibly powerful, but they aren't very intuitive and can ultimately end up making it easy for attackers to take your site down.
Let’s take the following regular expression as an example:
regex = /A(B|C+)+D/
This regular expression accomplishes the following:
AThe string must start with the letter 'A'(B|C+)+The string must then follow the letter A with either the letter 'B' or some number of occurrences of the letter 'C' (the+matches one or more times). The+at the end of this section states that we can look for one or more matches of this section.DFinally, we ensure this section of the string ends with a 'D'
The expression would match inputs such as ABBD, ABCCCCD, ABCBCCCD and ACCCCCD
It most cases, it doesn't take very long for a regex engine to find a match:
$ time node -e '/A(B|C+)+D/.test("ACCCCCCCCCCCCCCCCCCCCCCCCCCCCD")'
0.04s user 0.01s system 95% cpu 0.052 total
$ time node -e '/A(B|C+)+D/.test("ACCCCCCCCCCCCCCCCCCCCCCCCCCCCX")'
1.79s user 0.02s system 99% cpu 1.812 total
The entire process of testing it against a 30 characters long string takes around ~52ms. But when given an invalid string, it takes nearly two seconds to complete the test, over ten times as long as it took to test a valid string. The dramatic difference is due to the way regular expressions get evaluated.
Most Regex engines will work very similarly (with minor differences). The engine will match the first possible way to accept the current character and proceed to the next one. If it then fails to match the next one, it will backtrack and see if there was another way to digest the previous character. If it goes too far down the rabbit hole only to find out the string doesn’t match in the end, and if many characters have multiple valid regex paths, the number of backtracking steps can become very large, resulting in what is known as catastrophic backtracking.
Let's look at how our expression runs into this problem, using a shorter string: "ACCCX". While it seems fairly straightforward, there are still four different ways that the engine could match those three C's:
- CCC
- CC+C
- C+CC
- C+C+C.
The engine has to try each of those combinations to see if any of them potentially match against the expression. When you combine that with the other steps the engine must take, we can use RegEx 101 debugger to see the engine has to take a total of 38 steps before it can determine the string doesn't match.
From there, the number of steps the engine must use to validate a string just continues to grow.
| String | Number of C's | Number of steps |
|---|---|---|
| ACCCX | 3 | 38 |
| ACCCCX | 4 | 71 |
| ACCCCCX | 5 | 136 |
| ACCCCCCCCCCCCCCX | 14 | 65,553 |
By the time the string includes 14 C's, the engine has to take over 65,000 steps just to see if the string is valid. These extreme situations can cause them to work very slowly (exponentially related to input size, as shown above), allowing an attacker to exploit this and can cause the service to excessively consume CPU, resulting in a Denial of Service.
Remediation
Upgrade linkify-it to version 5.0.1 or higher.
References
Inefficient Algorithmic Complexity
Detailed paths
Overview
linkify-it is a Links recognition library with FULL unicode support
Affected versions of this package are vulnerable to Inefficient Algorithmic Complexity in the mailto: validator scan-loop on attacker-supplied text. An attacker can cause excessive CPU consumption by submitting specially crafted input that triggers repeated scanning of the remaining text.
Remediation
Upgrade linkify-it to version 5.0.2 or higher.
References
Prototype Pollution
Detailed paths
Overview
Affected versions of this package are vulnerable to Prototype Pollution via mergeObject(), which fails to validate keys before writing them to target objects. An attacker can supply a malicious source object containing a __proto__ key in a merge operation, injecting attacker-controlled properties into the prototype of the returned object and causing applications to inherit unintended values when accessing properties without own-property checks. We score this differently from NVD: prototype pollution that achieves property injection into Object.prototype with no authentication and no user interaction warrants a High integrity impact, consistent with the supplied CVSS vectors.
Details
Prototype Pollution is a vulnerability affecting JavaScript. Prototype Pollution refers to the ability to inject properties into existing JavaScript language construct prototypes, such as objects. JavaScript allows all Object attributes to be altered, including their magical attributes such as __proto__, constructor and prototype. An attacker manipulates these attributes to overwrite, or pollute, a JavaScript application object prototype of the base object by injecting other values. Properties on the Object.prototype are then inherited by all the JavaScript objects through the prototype chain. When that happens, this leads to either denial of service by triggering JavaScript exceptions, or it tampers with the application source code to force the code path that the attacker injects, thereby leading to remote code execution.
There are two main ways in which the pollution of prototypes occurs:
Unsafe
Objectrecursive mergeProperty definition by path
Unsafe Object recursive merge
The logic of a vulnerable recursive merge function follows the following high-level model:
merge (target, source)
foreach property of source
if property exists and is an object on both the target and the source
merge(target[property], source[property])
else
target[property] = source[property]
When the source object contains a property named __proto__ defined with Object.defineProperty() , the condition that checks if the property exists and is an object on both the target and the source passes and the merge recurses with the target, being the prototype of Object and the source of Object as defined by the attacker. Properties are then copied on the Object prototype.
Clone operations are a special sub-class of unsafe recursive merges, which occur when a recursive merge is conducted on an empty object: merge({},source).
lodash and Hoek are examples of libraries susceptible to recursive merge attacks.
Property definition by path
There are a few JavaScript libraries that use an API to define property values on an object based on a given path. The function that is generally affected contains this signature: theFunction(object, path, value)
If the attacker can control the value of “path”, they can set this value to __proto__.myValue. myValue is then assigned to the prototype of the class of the object.
Types of attacks
There are a few methods by which Prototype Pollution can be manipulated:
| Type | Origin | Short description |
|---|---|---|
| Denial of service (DoS) | Client | This is the most likely attack. DoS occurs when Object holds generic functions that are implicitly called for various operations (for example, toString and valueOf). The attacker pollutes Object.prototype.someattr and alters its state to an unexpected value such as Int or Object. In this case, the code fails and is likely to cause a denial of service. For example: if an attacker pollutes Object.prototype.toString by defining it as an integer, if the codebase at any point was reliant on someobject.toString() it would fail. |
| Remote Code Execution | Client | Remote code execution is generally only possible in cases where the codebase evaluates a specific attribute of an object, and then executes that evaluation. For example: eval(someobject.someattr). In this case, if the attacker pollutes Object.prototype.someattr they are likely to be able to leverage this in order to execute code. |
| Property Injection | Client | The attacker pollutes properties that the codebase relies on for their informative value, including security properties such as cookies or tokens. For example: if a codebase checks privileges for someuser.isAdmin, then when the attacker pollutes Object.prototype.isAdmin and sets it to equal true, they can then achieve admin privileges. |
Affected environments
The following environments are susceptible to a Prototype Pollution attack:
Application server
Web server
Web browser
How to prevent
Freeze the prototype— use
Object.freeze (Object.prototype).Require schema validation of JSON input.
Avoid using unsafe recursive merge functions.
Consider using objects without prototypes (for example,
Object.create(null)), breaking the prototype chain and preventing pollution.As a best practice use
Mapinstead ofObject.
For more information on this vulnerability type:
Arteau, Olivier. “JavaScript prototype pollution attack in NodeJS application.” GitHub, 26 May 2018
Remediation
There is no fixed version for deepmerge.
References
Inefficient Algorithmic Complexity
Detailed paths
Overview
brace-expansion is a Brace expansion as known from sh/bash
Affected versions of this package are vulnerable to Inefficient Algorithmic Complexity via the expand function. An attacker can cause excessive CPU consumption and block the event loop by supplying a specially crafted string containing multiple consecutive non-expanding '{}' brace groups. The max option does not prevent this issue, as it only limits the output size and not the computational workload.
Remediation
Upgrade brace-expansion to version 1.1.16, 2.1.2, 5.0.7 or higher.
References
Allocation of Resources Without Limits or Throttling
Detailed paths
Overview
brace-expansion is a Brace expansion as known from sh/bash
Affected versions of this package are vulnerable to Allocation of Resources Without Limits or Throttling in the expand() function and its recursive expand_ helper, which cap the number of results via the max option but do not bound the length of each result string. An attacker can crash the Node process with a fatal, uncatchable out-of-memory error by supplying a pattern that chains many brace groups, such as {a,b} repeated, keeping the result count under max while each result grows with the group count so total output scales unbounded. Exploitation requires the application to pass untrusted input to expand(), directly or transitively through minimatch or glob brace patterns.
Workaround
This vulnerability can be avoided by passing small explicit max and maxLength options to expand(), bounding both the number of results and the length of each so total output stays limited.
Remediation
Upgrade brace-expansion to version 1.1.16, 2.1.2, 5.0.8 or higher.
References
Allocation of Resources Without Limits or Throttling
Detailed paths
Overview
brace-expansion is a Brace expansion as known from sh/bash
Affected versions of this package are vulnerable to Allocation of Resources Without Limits or Throttling in the expand(), expand_(), combine(), and expandSequence() functions, which bound the accumulator where results are combined but not the intermediate arrays that feed it. An attacker can crash the process with an uncatchable out-of-memory error, or stall the event loop for minutes, by supplying a pattern with many comma-separated alternatives that each receive an independent maxLength allowance and accumulate without a cumulative limit, or a padded sequence whose generation ignores maxLength and does work proportional to max * width. Exploitation requires the application to pass untrusted input to expand(), directly or transitively through a glob or pattern-matching library.
Workaround
This vulnerability can be avoided by passing an explicitly small max together with a small maxLength to expand(), bounding both the result count and length, since a small maxLength alone is insufficient on affected versions where it is applied per alternative rather than cumulatively.
Note: This is a bypass of the fix for the vulnerability described in CVE-2026-14257.
Remediation
Upgrade brace-expansion to version 1.1.18, 2.1.4, 3.0.6, 5.0.9 or higher.
References
Uncontrolled Recursion
Detailed paths
Overview
brace-expansion is a Brace expansion as known from sh/bash
Affected versions of this package are vulnerable to Uncontrolled Recursion via uncontrolled recursion in expand_ when processing deeply nested brace patterns. An attacker can supply approximately 6 KB of deeply nested braces (e.g., { repeated ~3,200 times followed by a,b and the matching } characters) to exhaust the native call stack and crash the process with a RangeError: Maximum call stack size exceeded. The max and maxLength bounds do not prevent this because the stack is exhausted during recursive descent into sub-expansions, before the result set grows.
Remediation
Upgrade brace-expansion to version 1.1.20, 2.1.6, 3.0.8, 5.0.11 or higher.
References
Uncontrolled Recursion
Detailed paths
Overview
brace-expansion is a Brace expansion as known from sh/bash
Affected versions of this package are vulnerable to Uncontrolled Recursion via two distinct stack-exhaustion paths in parseCommaParts. In the first, the function recurses on the remainder of the string once per brace group, so a chain of approximately 7,000 groups (~29 KB of input) exhausts the native call stack and throws a RangeError. In the second, push.apply passes one argument per element, meaning a single large comma-separated array inside a brace group overflows the stack at a recursion depth of exactly one, requiring roughly 125,000 comma-separated elements. Neither the max nor maxLength options can bound either path because the crash occurs during parsing, before any expansion takes place.
Remediation
Upgrade brace-expansion to version 1.1.19, 2.1.5, 3.0.7, 5.0.10 or higher.
References
Improper Validation of Specified Index, Position, or Offset in Input
Detailed paths
Overview
uuid is a RFC4122 (v1, v4, and v5) compliant UUID library.
Affected versions of this package are vulnerable to Improper Validation of Specified Index, Position, or Offset in Input due to accepting external output buffers but not rejecting out-of-range writes (small buf or large offset). This inconsistency allows silent partial writes into caller-provided buffers.
PoC
cd /home/StrawHat/uuid
npm ci
npm run build
node --input-type=module -e "
import {v4,v5,v6} from './dist-node/index.js';
const ns='6ba7b810-9dad-11d1-80b4-00c04fd430c8';
for (const [name,fn] of [
['v4',()=>v4({},new Uint8Array(8),4)],
['v5',()=>v5('x',ns,new Uint8Array(8),4)],
['v6',()=>v6({},new Uint8Array(8),4)],
]) {
try { fn(); console.log(name,'NO_THROW'); }
catch(e){ console.log(name,'THREW',e.name); }
}"
Remediation
Upgrade uuid to version 11.1.1, 14.0.0 or higher.
References
Allocation of Resources Without Limits or Throttling
Detailed paths
Overview
qs is a querystring parser that supports nesting and arrays, with a depth limit.
Affected versions of this package are vulnerable to Allocation of Resources Without Limits or Throttling in the parseArrayValue() comma-parsing logic, which applies the arrayLimit and throwOnLimitExceeded checks only to flat values, so a bracket-key input such as a[]=1,2,3,4 is treated as non-flat and its comma-split inner array is wrapped after parsing without ever being length-checked. An attacker can exceed the configured array limit and force excessive memory allocation by supplying a query string or form body that uses the bracket-key comma form, for example a[]=1,2,3,.... This requires the application to parse untrusted input with the comma: true option enabled alongside a configured arrayLimit or throwOnLimitExceeded.
PoC
const qs = require('qs')
const options = { comma: true, arrayLimit: 3, throwOnLimitExceeded: true }
const result = qs.parse('a[]=1,2,3,4', options)
console.log(result.a[0].length) // 4; expected RangeError
const big = qs.parse('a[]=' + '1,'.repeat(1000000) + '1', { comma: true, arrayLimit: 20 })
console.log(big.a[0].length) // 1000001
Details
Denial of Service (DoS) describes a family of attacks, all aimed at making a system inaccessible to its intended and legitimate users.
Unlike other vulnerabilities, DoS attacks usually do not aim at breaching security. Rather, they are focused on making websites and services unavailable to genuine users resulting in downtime.
One popular Denial of Service vulnerability is DDoS (a Distributed Denial of Service), an attack that attempts to clog network pipes to the system by generating a large volume of traffic from many machines.
When it comes to open source libraries, DoS vulnerabilities allow attackers to trigger such a crash or crippling of the service by using a flaw either in the application code or from the use of open source libraries.
Two common types of DoS vulnerabilities:
High CPU/Memory Consumption- An attacker sending crafted requests that could cause the system to take a disproportionate amount of time to process. For example, commons-fileupload:commons-fileupload.
Crash - An attacker sending crafted requests that could cause the system to crash. For Example, npm
wspackage
Remediation
Upgrade qs to version 6.16.0 or higher.
References
Uncaught Exception
Detailed paths
Overview
qs is a querystring parser that supports nesting and arrays, with a depth limit.
Affected versions of this package are vulnerable to Uncaught Exception in the isBuffer() function in lib/utils.js, which calls obj.constructor.isBuffer(obj) without checking that it is callable, reached from stringify() at lib/stringify.js:127. An attacker can throw an uncaught TypeError that fails each request with HTTP 500, and terminates the worker process when stringify() runs in an unguarded async context, by supplying a query string such as x[constructor][isBuffer]=y that sets constructor.isBuffer to a non-function value. This requires the application to call qs.parse() with plainObjects: true or allowPrototypes: true, which preserves the constructor own property, and to then pass the parsed result to qs.stringify().
Details
Denial of Service (DoS) describes a family of attacks, all aimed at making a system inaccessible to its intended and legitimate users.
Unlike other vulnerabilities, DoS attacks usually do not aim at breaching security. Rather, they are focused on making websites and services unavailable to genuine users resulting in downtime.
One popular Denial of Service vulnerability is DDoS (a Distributed Denial of Service), an attack that attempts to clog network pipes to the system by generating a large volume of traffic from many machines.
When it comes to open source libraries, DoS vulnerabilities allow attackers to trigger such a crash or crippling of the service by using a flaw either in the application code or from the use of open source libraries.
Two common types of DoS vulnerabilities:
High CPU/Memory Consumption- An attacker sending crafted requests that could cause the system to take a disproportionate amount of time to process. For example, commons-fileupload:commons-fileupload.
Crash - An attacker sending crafted requests that could cause the system to crash. For Example, npm
wspackage
Remediation
Upgrade qs to version 6.16.0 or higher.
References
Improper Validation of Specified Type of Input
Detailed paths
Overview
Affected versions of this package are vulnerable to Improper Validation of Specified Type of Input in the calls plugin when handling websocket messages containing malformed msgpack frames. An attacker can cause the server to consume excessive memory and crash by sending specially crafted websocket requests.
Remediation
There is no fixed version for github.com/vmihailenco/msgpack/v5.
References
Incorrect Authorization
Detailed paths
Overview
Affected versions of this package are vulnerable to Incorrect Authorization in the ServeHTTP method of ServeMux (runtime/mux.go), which rewrites r.Method from the client-supplied X-HTTP-Method-Override header on form-urlencoded POST requests without restricting the allowed methods. An attacker can reach handlers for restricted verbs such as DELETE, PUT, or PATCH, bypassing method-based access controls enforced at an upstream proxy or WAF, by sending a POST request with Content-Type: application/x-www-form-urlencoded and the override header set to the target method. This requires a deployment where a perimeter proxy or WAF filters on the wire method while trusting the gateway downstream, and a handler must exist for the overridden method.
Note: The WithDisablePathLengthFallback is added in version 2.29.0 but it is disabled by default.
Workaround
This vulnerability can be avoided by stripping the X-HTTP-Method-Override header at the perimeter proxy or WAF, so the enforced wire method is the one the gateway routes on.
Remediation
There is no fixed version for github.com/grpc-ecosystem/grpc-gateway/v2/runtime.
References
Incorrect Authorization
Detailed paths
Overview
Affected versions of this package are vulnerable to Incorrect Authorization in the ServeHTTP method of ServeMux (runtime/mux.go), which rewrites r.Method from the client-supplied X-HTTP-Method-Override header on form-urlencoded POST requests without restricting the allowed methods. An attacker can reach handlers for restricted verbs such as DELETE, PUT, or PATCH, bypassing method-based access controls enforced at an upstream proxy or WAF, by sending a POST request with Content-Type: application/x-www-form-urlencoded and the override header set to the target method. This requires a deployment where a perimeter proxy or WAF filters on the wire method while trusting the gateway downstream, and a handler must exist for the overridden method.
Note: The WithDisablePathLengthFallback is added in version 2.29.0 but it is disabled by default.
Workaround
This vulnerability can be avoided by stripping the X-HTTP-Method-Override header at the perimeter proxy or WAF, so the enforced wire method is the one the gateway routes on.
Remediation
There is no fixed version for github.com/grpc-ecosystem/grpc-gateway/runtime.
References
Regular Expression Denial of Service (ReDoS)
Detailed paths
Overview
foundation-sites is a responsive front-end framework
Affected versions of this package are vulnerable to Regular Expression Denial of Service (ReDoS) due to inefficient backtracking in the regular expressions used in URL forms.
PoC
https://www.''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
Details
Denial of Service (DoS) describes a family of attacks, all aimed at making a system inaccessible to its original and legitimate users. There are many types of DoS attacks, ranging from trying to clog the network pipes to the system by generating a large volume of traffic from many machines (a Distributed Denial of Service - DDoS - attack) to sending crafted requests that cause a system to crash or take a disproportional amount of time to process.
The Regular expression Denial of Service (ReDoS) is a type of Denial of Service attack. Regular expressions are incredibly powerful, but they aren't very intuitive and can ultimately end up making it easy for attackers to take your site down.
Let’s take the following regular expression as an example:
regex = /A(B|C+)+D/
This regular expression accomplishes the following:
AThe string must start with the letter 'A'(B|C+)+The string must then follow the letter A with either the letter 'B' or some number of occurrences of the letter 'C' (the+matches one or more times). The+at the end of this section states that we can look for one or more matches of this section.DFinally, we ensure this section of the string ends with a 'D'
The expression would match inputs such as ABBD, ABCCCCD, ABCBCCCD and ACCCCCD
It most cases, it doesn't take very long for a regex engine to find a match:
$ time node -e '/A(B|C+)+D/.test("ACCCCCCCCCCCCCCCCCCCCCCCCCCCCD")'
0.04s user 0.01s system 95% cpu 0.052 total
$ time node -e '/A(B|C+)+D/.test("ACCCCCCCCCCCCCCCCCCCCCCCCCCCCX")'
1.79s user 0.02s system 99% cpu 1.812 total
The entire process of testing it against a 30 characters long string takes around ~52ms. But when given an invalid string, it takes nearly two seconds to complete the test, over ten times as long as it took to test a valid string. The dramatic difference is due to the way regular expressions get evaluated.
Most Regex engines will work very similarly (with minor differences). The engine will match the first possible way to accept the current character and proceed to the next one. If it then fails to match the next one, it will backtrack and see if there was another way to digest the previous character. If it goes too far down the rabbit hole only to find out the string doesn’t match in the end, and if many characters have multiple valid regex paths, the number of backtracking steps can become very large, resulting in what is known as catastrophic backtracking.
Let's look at how our expression runs into this problem, using a shorter string: "ACCCX". While it seems fairly straightforward, there are still four different ways that the engine could match those three C's:
- CCC
- CC+C
- C+CC
- C+C+C.
The engine has to try each of those combinations to see if any of them potentially match against the expression. When you combine that with the other steps the engine must take, we can use RegEx 101 debugger to see the engine has to take a total of 38 steps before it can determine the string doesn't match.
From there, the number of steps the engine must use to validate a string just continues to grow.
| String | Number of C's | Number of steps |
|---|---|---|
| ACCCX | 3 | 38 |
| ACCCCX | 4 | 71 |
| ACCCCCX | 5 | 136 |
| ACCCCCCCCCCCCCCX | 14 | 65,553 |
By the time the string includes 14 C's, the engine has to take over 65,000 steps just to see if the string is valid. These extreme situations can cause them to work very slowly (exponentially related to input size, as shown above), allowing an attacker to exploit this and can cause the service to excessively consume CPU, resulting in a Denial of Service.
Remediation
There is no fixed version for foundation-sites.
References
CRLF Injection
Detailed paths
Overview
Affected versions of this package are vulnerable to CRLF Injection via the _multiPartHeader function when untrusted input is provided via field or filename to FormData#append. An attacker can inject additional headers or multipart parts by including carriage returns, line feeds, or double quotes in the input. This can allow the modification or addition of form fields visible to downstream parsers.
PoC
const FormData = require('form-data');
const form = new FormData();
form.append('email"\r\nX-Injected: true\r\nfake="', 'user@example.com');
console.log(form.getBuffer().toString());
Remediation
Upgrade form-data to version 2.5.6, 3.0.5, 4.0.6 or higher.
References
Regular Expression Denial of Service (ReDoS)
Detailed paths
Overview
brace-expansion is a Brace expansion as known from sh/bash
Affected versions of this package are vulnerable to Regular Expression Denial of Service (ReDoS) via the expand_ function, which implements a Bash quirk where a brace group followed by a comma set (e.g. {a},b}) causes the parser to rewrite the input string and restart the scan, absorbing one closing brace per pass. Because each pass re-reads the entire string and the string itself grows by approximately 25 characters per rewrite (due to the escClose sentinel), the work is quadratic in the number of trailing braces, allowing an attacker to block the event loop with a small input. An input of the form '{a}' + '}'.repeat(128000) + ',z}' takes approximately 27 seconds to process while producing only two results, and neither the existing max nor maxLength guards can prevent this because the cost is incurred during parsing before any result set is produced.
Details
Denial of Service (DoS) describes a family of attacks, all aimed at making a system inaccessible to its original and legitimate users. There are many types of DoS attacks, ranging from trying to clog the network pipes to the system by generating a large volume of traffic from many machines (a Distributed Denial of Service - DDoS - attack) to sending crafted requests that cause a system to crash or take a disproportional amount of time to process.
The Regular expression Denial of Service (ReDoS) is a type of Denial of Service attack. Regular expressions are incredibly powerful, but they aren't very intuitive and can ultimately end up making it easy for attackers to take your site down.
Let’s take the following regular expression as an example:
regex = /A(B|C+)+D/
This regular expression accomplishes the following:
AThe string must start with the letter 'A'(B|C+)+The string must then follow the letter A with either the letter 'B' or some number of occurrences of the letter 'C' (the+matches one or more times). The+at the end of this section states that we can look for one or more matches of this section.DFinally, we ensure this section of the string ends with a 'D'
The expression would match inputs such as ABBD, ABCCCCD, ABCBCCCD and ACCCCCD
It most cases, it doesn't take very long for a regex engine to find a match:
$ time node -e '/A(B|C+)+D/.test("ACCCCCCCCCCCCCCCCCCCCCCCCCCCCD")'
0.04s user 0.01s system 95% cpu 0.052 total
$ time node -e '/A(B|C+)+D/.test("ACCCCCCCCCCCCCCCCCCCCCCCCCCCCX")'
1.79s user 0.02s system 99% cpu 1.812 total
The entire process of testing it against a 30 characters long string takes around ~52ms. But when given an invalid string, it takes nearly two seconds to complete the test, over ten times as long as it took to test a valid string. The dramatic difference is due to the way regular expressions get evaluated.
Most Regex engines will work very similarly (with minor differences). The engine will match the first possible way to accept the current character and proceed to the next one. If it then fails to match the next one, it will backtrack and see if there was another way to digest the previous character. If it goes too far down the rabbit hole only to find out the string doesn’t match in the end, and if many characters have multiple valid regex paths, the number of backtracking steps can become very large, resulting in what is known as catastrophic backtracking.
Let's look at how our expression runs into this problem, using a shorter string: "ACCCX". While it seems fairly straightforward, there are still four different ways that the engine could match those three C's:
- CCC
- CC+C
- C+CC
- C+C+C.
The engine has to try each of those combinations to see if any of them potentially match against the expression. When you combine that with the other steps the engine must take, we can use RegEx 101 debugger to see the engine has to take a total of 38 steps before it can determine the string doesn't match.
From there, the number of steps the engine must use to validate a string just continues to grow.
| String | Number of C's | Number of steps |
|---|---|---|
| ACCCX | 3 | 38 |
| ACCCCX | 4 | 71 |
| ACCCCCX | 5 | 136 |
| ACCCCCCCCCCCCCCX | 14 | 65,553 |
By the time the string includes 14 C's, the engine has to take over 65,000 steps just to see if the string is valid. These extreme situations can cause them to work very slowly (exponentially related to input size, as shown above), allowing an attacker to exploit this and can cause the service to excessively consume CPU, resulting in a Denial of Service.
Remediation
Upgrade brace-expansion to version 1.1.21, 2.1.7, 3.0.9, 5.0.12 or higher.