Vulnerability · Published Apr 23, 2026 · Assigned by GitHub_M

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

Medium 5.9

In plain English

A medium-severity security flaw in node-oauth2-server from node-oauth. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 18% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)5.9Medium

Exploit odds (30 days)0.3%top 82.3% of all CVEs

Exploited in the wildNo reportsCISA SSVC: poc

Attack toolingNoneno public tooling known

Official 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.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
npm	@node-oauth/oauth2-server	5.3.0	GHSA-jhm7-29pj-4xvf

Affected products (as reported)

Vendor	Product	Versions
node-oauth	node-oauth2-server	< 5.3.0

Weakness: CWE-307, CWE-1289 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

References

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