# Snyk test report

November 2nd 2025, 12:27:05 am (UTC+00:00)

Scanned the following paths:

- /argo-cd/argoproj/argo-cd/v3/go.mod (gomodules)
- /argo-cd/argoproj/argo-cd/get-previous-release/hack/get-previous-release/go.mod (gomodules)
- /argo-cd/ui/yarn.lock (yarn)

11 known vulnerabilities
34 vulnerable dependency paths
2104 dependencies

## Predictable Value Range from Previous Values

critical severity

- Manifest file: /argo-cd › ui/yarn.lock
- Package Manager: npm
- Vulnerable module: form-data
- Introduced through: argo-cd-ui@1.0.0, superagent@8.1.2 and others

### Detailed paths

- Introduced through: argo-cd-ui@1.0.0 › superagent@8.1.2 › form-data@4.0.0

## Overview

Affected versions of this package are vulnerable to Predictable Value Range from Previous Values via the `boundary` value, which uses `Math.random()`. An attacker can manipulate HTTP request boundaries by exploiting predictable values, potentially leading to HTTP parameter pollution.

## Remediation

Upgrade `form-data` to version 2.5.4, 3.0.4, 4.0.4 or higher.

## References

- GitHub Commit
- GitHub Commit
- GitHub Commit
- POC
- Vulnerable Code

More about this vulnerability

## Improper Handling of Unexpected Data Type

high severity

- Manifest file: /argo-cd/argoproj/argo-cd/v3 › go.mod
- Package Manager: golang
- Vulnerable module: golang.org/x/crypto/ssh/agent
- Introduced through: github.com/argoproj/argo-cd/v3@0.0.0, code.gitea.io/sdk/gitea@0.21.0 and others

### Detailed paths

- Introduced through: github.com/argoproj/argo-cd/v3@0.0.0 › code.gitea.io/sdk/gitea@0.21.0 › golang.org/x/crypto/ssh/agent@0.39.0
- Introduced through: github.com/argoproj/argo-cd/v3@0.0.0 › github.com/go-git/go-git/v5/plumbing/transport/ssh@5.14.0 › github.com/xanzy/ssh-agent@0.3.3 › golang.org/x/crypto/ssh/agent@0.39.0
- Introduced through: github.com/argoproj/argo-cd/v3@0.0.0 › github.com/go-git/go-git/v5/plumbing/transport/client@5.14.0 › github.com/go-git/go-git/v5/plumbing/transport/ssh@5.14.0 › github.com/xanzy/ssh-agent@0.3.3 › golang.org/x/crypto/ssh/agent@0.39.0
- Introduced through: github.com/argoproj/argo-cd/v3@0.0.0 › github.com/go-git/go-git/v5@5.14.0 › github.com/go-git/go-git/v5/plumbing/transport/client@5.14.0 › github.com/go-git/go-git/v5/plumbing/transport/ssh@5.14.0 › github.com/xanzy/ssh-agent@0.3.3 › golang.org/x/crypto/ssh/agent@0.39.0

## Overview

Affected versions of this package are vulnerable to Improper Handling of Unexpected Data Type when functions including `List()` and `SignWithFlags()` process `*successAgentMsg`. This can be triggered by a malicious agent sending a single `0x06` byte (`SSH_AGENT_SUCCESS`), which is unmarshalled into a `*successAgentMsg`, causing a panic and client crash.

## 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 `ws` package

## Remediation

Upgrade `golang.org/x/crypto/ssh/agent` to version 0.43.0 or higher.

## References

- GitHub Commit
- GitHub Issue

More about this vulnerability

## Prototype Pollution

medium severity

- Manifest file: /argo-cd › ui/yarn.lock
- Package Manager: npm
- Vulnerable module: min-document
- Introduced through: argo-cd-ui@1.0.0, react-hot-loader@3.1.3 and others

### Detailed paths

- Introduced through: argo-cd-ui@1.0.0 › react-hot-loader@3.1.3 › global@4.4.0 › min-document@2.19.0

## Overview

Affected versions of this package are vulnerable to Prototype Pollution via the `removeAttributeNS` function. An attacker can manipulate the prototype chain of JavaScript objects, potentially causing a denial-of-service attack by supplying malicious input that targets the `__proto__` property during namespace attribute removal.

Notes:

This vulnerability is only exploitable if user input is passed without sanitization to the affected functions. The PoC has been validated as a theoretical vector, and a fixed version has been released.

## 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 `Object` recursive merge

- Property 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

1. Freeze the prototype— use `Object.freeze (Object.prototype)`.

2. Require schema validation of JSON input.

3. Avoid using unsafe recursive merge functions.

4. Consider using objects without prototypes (for example, `Object.create(null)`), breaking the prototype chain and preventing pollution.

5. As a best practice use `Map` instead of `Object`.

### For more information on this vulnerability type:

Arteau, Oliver. “JavaScript prototype pollution attack in NodeJS application.” GitHub, 26 May 2018

## Remediation

There is no fixed version for `min-document`.

## References

- Github Commit
- GitHub Issue
- POC
- Vulnerable Code

More about this vulnerability

## MPL-2.0 license

medium severity

- Manifest file: /argo-cd/argoproj/argo-cd/v3 › go.mod
- Package Manager: golang
- Module: github.com/r3labs/diff/v3
- Introduced through: github.com/argoproj/argo-cd/v3@0.0.0 and github.com/r3labs/diff/v3@3.0.1

### Detailed paths

- Introduced through: github.com/argoproj/argo-cd/v3@0.0.0 › github.com/r3labs/diff/v3@3.0.1

MPL-2.0 license

More about this vulnerability

## MPL-2.0 license

medium severity

- Manifest file: /argo-cd/argoproj/argo-cd/v3 › go.mod
- Package Manager: golang
- Module: github.com/hashicorp/go-version
- Introduced through: github.com/argoproj/argo-cd/v3@0.0.0, code.gitea.io/sdk/gitea@0.21.0 and others

### Detailed paths

- Introduced through: github.com/argoproj/argo-cd/v3@0.0.0 › code.gitea.io/sdk/gitea@0.21.0 › github.com/hashicorp/go-version@1.7.0

MPL-2.0 license

More about this vulnerability

## MPL-2.0 license

medium severity

- Manifest file: /argo-cd/argoproj/argo-cd/v3 › go.mod
- Package Manager: golang
- Module: github.com/hashicorp/go-retryablehttp
- Introduced through: github.com/argoproj/argo-cd/v3@0.0.0 and github.com/hashicorp/go-retryablehttp@0.7.7

### Detailed paths

- Introduced through: github.com/argoproj/argo-cd/v3@0.0.0 › github.com/hashicorp/go-retryablehttp@0.7.7
- Introduced through: github.com/argoproj/argo-cd/v3@0.0.0 › github.com/argoproj/notifications-engine/pkg/services@#87bf0576a872 › github.com/hashicorp/go-retryablehttp@0.7.7
- Introduced through: github.com/argoproj/argo-cd/v3@0.0.0 › gitlab.com/gitlab-org/api/client-go@0.130.1 › github.com/hashicorp/go-retryablehttp@0.7.7
- Introduced through: github.com/argoproj/argo-cd/v3@0.0.0 › github.com/argoproj/notifications-engine/pkg/subscriptions@#87bf0576a872 › github.com/argoproj/notifications-engine/pkg/services@#87bf0576a872 › github.com/hashicorp/go-retryablehttp@0.7.7
- Introduced through: github.com/argoproj/argo-cd/v3@0.0.0 › github.com/argoproj/notifications-engine/pkg/cmd@#87bf0576a872 › github.com/argoproj/notifications-engine/pkg/services@#87bf0576a872 › github.com/hashicorp/go-retryablehttp@0.7.7
- Introduced through: github.com/argoproj/argo-cd/v3@0.0.0 › github.com/argoproj/notifications-engine/pkg/services@#87bf0576a872 › github.com/opsgenie/opsgenie-go-sdk-v2/client@1.2.23 › github.com/hashicorp/go-retryablehttp@0.7.7
- Introduced through: github.com/argoproj/argo-cd/v3@0.0.0 › github.com/argoproj/notifications-engine/pkg/api@#87bf0576a872 › github.com/argoproj/notifications-engine/pkg/subscriptions@#87bf0576a872 › github.com/argoproj/notifications-engine/pkg/services@#87bf0576a872 › github.com/hashicorp/go-retryablehttp@0.7.7
- Introduced through: github.com/argoproj/argo-cd/v3@0.0.0 › github.com/argoproj/notifications-engine/pkg/controller@#87bf0576a872 › github.com/argoproj/notifications-engine/pkg/subscriptions@#87bf0576a872 › github.com/argoproj/notifications-engine/pkg/services@#87bf0576a872 › github.com/hashicorp/go-retryablehttp@0.7.7
- Introduced through: github.com/argoproj/argo-cd/v3@0.0.0 › github.com/argoproj/notifications-engine/pkg/subscriptions@#87bf0576a872 › github.com/argoproj/notifications-engine/pkg/services@#87bf0576a872 › github.com/opsgenie/opsgenie-go-sdk-v2/client@1.2.23 › github.com/hashicorp/go-retryablehttp@0.7.7
- Introduced through: github.com/argoproj/argo-cd/v3@0.0.0 › github.com/argoproj/notifications-engine/pkg/cmd@#87bf0576a872 › github.com/argoproj/notifications-engine/pkg/services@#87bf0576a872 › github.com/opsgenie/opsgenie-go-sdk-v2/client@1.2.23 › github.com/hashicorp/go-retryablehttp@0.7.7
- Introduced through: github.com/argoproj/argo-cd/v3@0.0.0 › github.com/argoproj/notifications-engine/pkg/api@#87bf0576a872 › github.com/argoproj/notifications-engine/pkg/subscriptions@#87bf0576a872 › github.com/argoproj/notifications-engine/pkg/services@#87bf0576a872 › github.com/opsgenie/opsgenie-go-sdk-v2/client@1.2.23 › github.com/hashicorp/go-retryablehttp@0.7.7
- Introduced through: github.com/argoproj/argo-cd/v3@0.0.0 › github.com/argoproj/notifications-engine/pkg/controller@#87bf0576a872 › github.com/argoproj/notifications-engine/pkg/subscriptions@#87bf0576a872 › github.com/argoproj/notifications-engine/pkg/services@#87bf0576a872 › github.com/opsgenie/opsgenie-go-sdk-v2/client@1.2.23 › github.com/hashicorp/go-retryablehttp@0.7.7

MPL-2.0 license

More about this vulnerability

## MPL-2.0 license

medium severity

- Manifest file: /argo-cd/argoproj/argo-cd/v3 › go.mod
- Package Manager: golang
- Module: github.com/hashicorp/go-cleanhttp
- Introduced through: github.com/argoproj/argo-cd/v3@0.0.0, github.com/hashicorp/go-retryablehttp@0.7.7 and others

### Detailed paths

- Introduced through: github.com/argoproj/argo-cd/v3@0.0.0 › github.com/hashicorp/go-retryablehttp@0.7.7 › github.com/hashicorp/go-cleanhttp@0.5.2
- Introduced through: github.com/argoproj/argo-cd/v3@0.0.0 › gitlab.com/gitlab-org/api/client-go@0.130.1 › github.com/hashicorp/go-cleanhttp@0.5.2
- Introduced through: github.com/argoproj/argo-cd/v3@0.0.0 › gitlab.com/gitlab-org/api/client-go@0.130.1 › github.com/hashicorp/go-retryablehttp@0.7.7 › github.com/hashicorp/go-cleanhttp@0.5.2
- Introduced through: github.com/argoproj/argo-cd/v3@0.0.0 › github.com/argoproj/notifications-engine/pkg/services@#87bf0576a872 › github.com/opsgenie/opsgenie-go-sdk-v2/client@1.2.23 › github.com/hashicorp/go-retryablehttp@0.7.7 › github.com/hashicorp/go-cleanhttp@0.5.2
- Introduced through: github.com/argoproj/argo-cd/v3@0.0.0 › github.com/argoproj/notifications-engine/pkg/subscriptions@#87bf0576a872 › github.com/argoproj/notifications-engine/pkg/services@#87bf0576a872 › github.com/opsgenie/opsgenie-go-sdk-v2/client@1.2.23 › github.com/hashicorp/go-retryablehttp@0.7.7 › github.com/hashicorp/go-cleanhttp@0.5.2
- Introduced through: github.com/argoproj/argo-cd/v3@0.0.0 › github.com/argoproj/notifications-engine/pkg/cmd@#87bf0576a872 › github.com/argoproj/notifications-engine/pkg/services@#87bf0576a872 › github.com/opsgenie/opsgenie-go-sdk-v2/client@1.2.23 › github.com/hashicorp/go-retryablehttp@0.7.7 › github.com/hashicorp/go-cleanhttp@0.5.2
- Introduced through: github.com/argoproj/argo-cd/v3@0.0.0 › github.com/argoproj/notifications-engine/pkg/api@#87bf0576a872 › github.com/argoproj/notifications-engine/pkg/subscriptions@#87bf0576a872 › github.com/argoproj/notifications-engine/pkg/services@#87bf0576a872 › github.com/opsgenie/opsgenie-go-sdk-v2/client@1.2.23 › github.com/hashicorp/go-retryablehttp@0.7.7 › github.com/hashicorp/go-cleanhttp@0.5.2
- Introduced through: github.com/argoproj/argo-cd/v3@0.0.0 › github.com/argoproj/notifications-engine/pkg/controller@#87bf0576a872 › github.com/argoproj/notifications-engine/pkg/subscriptions@#87bf0576a872 › github.com/argoproj/notifications-engine/pkg/services@#87bf0576a872 › github.com/opsgenie/opsgenie-go-sdk-v2/client@1.2.23 › github.com/hashicorp/go-retryablehttp@0.7.7 › github.com/hashicorp/go-cleanhttp@0.5.2

MPL-2.0 license

More about this vulnerability

## MPL-2.0 license

medium severity

- Manifest file: /argo-cd/argoproj/argo-cd/v3 › go.mod
- Package Manager: golang
- Module: github.com/gosimple/slug
- Introduced through: github.com/argoproj/argo-cd/v3@0.0.0 and github.com/gosimple/slug@1.15.0

### Detailed paths

- Introduced through: github.com/argoproj/argo-cd/v3@0.0.0 › github.com/gosimple/slug@1.15.0

MPL-2.0 license

More about this vulnerability

## Regular Expression Denial of Service (ReDoS)

medium severity

- Manifest file: /argo-cd › ui/yarn.lock
- Package Manager: npm
- Vulnerable module: foundation-sites
- Introduced through: argo-cd-ui@1.0.0 and foundation-sites@6.8.1

### Detailed paths

- Introduced through: argo-cd-ui@1.0.0 › foundation-sites@6.8.1
- Introduced through: argo-cd-ui@1.0.0 › argo-ui@1.0.0 › foundation-sites@6.8.1

## 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:

- `A` The 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.
- `D` Finally, 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:

1. CCC
2. CC+C
3. C+CC
4. 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

- GitHub Advisory
- GitHub Issue
- Vulnerable Code

More about this vulnerability

## Insecure Randomness

low severity

- Manifest file: /argo-cd › ui/yarn.lock
- Package Manager: npm
- Vulnerable module: formidable
- Introduced through: argo-cd-ui@1.0.0, superagent@8.1.2 and others

### Detailed paths

- Introduced through: argo-cd-ui@1.0.0 › superagent@8.1.2 › formidable@2.1.2

## Overview

Affected versions of this package are vulnerable to Insecure Randomness due to its use of the `hexoid()` function in the generation of fingerprint IDs.

## Remediation

Upgrade `formidable` to version 2.1.3, 3.5.3 or higher.

## References

- GitHub Commit
- Vulnerability Report

More about this vulnerability

## Regular Expression Denial of Service (ReDoS)

low severity

- Manifest file: /argo-cd › ui/yarn.lock
- Package Manager: npm
- Vulnerable module: brace-expansion
- Introduced through: argo-cd-ui@1.0.0, minimatch@3.1.2 and others

### Detailed paths

- Introduced through: argo-cd-ui@1.0.0 › minimatch@3.1.2 › brace-expansion@1.1.11
- Introduced through: argo-cd-ui@1.0.0 › redoc@2.4.0 › @redocly/openapi-core@1.30.0 › minimatch@5.1.6 › brace-expansion@2.0.1

## 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) in the `expand()` function, which is prone to catastrophic backtracking on very long malicious inputs.

## PoC

    import index from "./index.js";

            let str = "{a}" + ",".repeat(100000) + "\u0000";

            let startTime = performance.now();

            const result = index(str);

            let endTime = performance.now();

            let timeTaken = endTime - startTime;

            console.log(`匹配耗时: ${timeTaken.toFixed(3)} 毫秒`);

## 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:

- `A` The 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.
- `D` Finally, 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:

1. CCC
2. CC+C
3. C+CC
4. 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 1.1.12, 2.0.2, 3.0.1, 4.0.1 or higher.

## References

- GitHub Advisory
- GitHub Commit
- GitHub Gist
- GitHub PR

More about this vulnerability