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
CVSS Score
Published: April 23, 2026 at 06:33 PM UTC
Updated: October 26, 2026 at 09:10 PM UTC
2 products affected across 1 vendorNode Oauth /oauth2 ServerOauth Node Oauth OAUTH2 Server

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Severity
MEDIUM5.9
Exploit prediction
EPSS 0.3%
SSVC
PoC

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

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

v < 5.3.0
Affected range stops below 5.3.0, so it looks safe — our inference, not a vendor statement
v < 5.3.0
Affected range stops below 5.3.0, so it looks safe — our inference, not a vendor statement

Remediation

No guide yet

No remediation guidance has been written for this CVE yet. What the record does show:

References (1)

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

SSVC — Action Prioritization

SSVCPoCNot automatablePartial impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

5.9MEDIUMGitHub_M
Attack Vector
NETWORK
Complexity
HIGH
Privileges
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality
HIGH
Integrity
NONE
Availability
NONE
Vector?

Quick Info

StatusANALYZED
CWE
CWE-307CWE-1289

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