# CVE-2024-21491: svix vulnerable to Authentication Bypass

> Attackers can bypass webhook signature verification in the Svix Rust library by exploiting a flawed comparison logic, allowing unauthorized webhook processing.

- **Severity:** Medium 5.9 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:L/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 13 Feb 2024
- **Updated:** 9 May 2025
- **Also known as:** GHSA-747x-5m58-mq97, GHSA-w277-wpqf-rcfv, RUSTSEC-2024-0010

## What is CVE-2024-21491?

CVE-2024-21491 is a medium-severity authentication bypass vulnerability in svix, published on 13 Feb 2024. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official description

Versions of the package svix before 1.17.0 are vulnerable to Authentication Bypass due to an issue in the verify function where signatures of different lengths are incorrectly compared. An attacker can bypass signature verification by providing a shorter signature that matches the beginning of the actual signature.

**Note:**

The attacker would need to know a victim uses the Rust library for verification,no easy way to automatically check that; and uses webhooks by a service that uses Svix, and then figure out a way to craft a malicious payload that will actually include all of the correct identifiers needed to trick the receivers to cause actual issues.

Weakness: CWE-347 (Improper Verification of Cryptographic Signature), CWE-288 (Authentication Bypass Using an Alternate Path or Channel)

## Which versions are affected by CVE-2024-21491?

5 open source packages ship an affected version, including svix. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `svix` | crates.io | All versions | 1.17.0 |
| `svix` | crates.io | All versions | 1.17.0 |
| `svix` | crates.io | All versions | 1.17.0 |
| `svix` | crates.io | All versions | 1.17.0 |
| `svix` | crates.io | From 0.0.0-0 | 1.17.0 |

Products: Svix Svix-Webhooks.

## How do I fix CVE-2024-21491?

Upgrade svix to 1.17.0 or later.

## Is CVE-2024-21491 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2024-21491 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2024-21491 and fix it if it is affected.

What it is: CVE-2024-21491 is a medium-severity authentication bypass vulnerability in svix, published on 13 Feb 2024. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2024-21491 exists.

Affected packages and fixed versions:
- svix (crates.io): affected all versions; fixed in 1.17.0
- svix (crates.io): affected all versions; fixed in 1.17.0
- svix (crates.io): affected all versions; fixed in 1.17.0
- svix (crates.io): affected all versions; fixed in 1.17.0
- svix (crates.io): affected from 0.0.0-0; fixed in 1.17.0

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2024-21491/ (Markdown: https://insights.sbomify.com/CVE-2024-21491/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2024-21491
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2024-21491
- OSV: https://osv.dev/vulnerability/CVE-2024-21491

---
From sbomify Insights: https://insights.sbomify.com/CVE-2024-21491/
Summaries are generated and may contain mistakes; the official description above is the record.