NIST deprecates RSA-2048 from 2030. Find every one of them before attackers do.
📦
📦 npm
Not in CISA KEV
MEDIUM severity

CVE-2026-41213 — @node-oauth/oauth2-server

MEDIUM

CVE-2026-41213 is a medium-severity (CVSS 5.9) CWE-307 vulnerability in @node-oauth/oauth2-server. A fix is available for @node-oauth/oauth2-server — see the affected versions and patch details below.

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

Also known asGHSA-jhm7-29pj-4xvf
Published
Updated
Affected
1 pkg
Patched
1 / 1
Exploits
None indexed
Exploitation data as of Nov 3, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

Proof-of-concept exploit code exists

  • CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-41213.

EPSS Exploitation Probability

via FIRST.org ↗
0.3%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs18th percentile — riskier than 18% of all scored CVEsHighest risk
0.00%0.28%0.56%0.85%0.1%0.3%May 26Sep 26Nov 26

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

1 pkg affected

How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.

27other npm packages depend on this — each one inherits the vulnerability until it's patched upstream
@node-oauth/oauth2-servernpm
268Kdownloads / week

Description

Summary

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.

Root cause

  1. lib/pkce/pkce.js (getHashForCodeChallenge) only checks that verifier is a non-empty string before hashing for S256; it does not enforce RFC7636 ABNF (43..128 unreserved chars).
  2. lib/grant-types/authorization-code-grant-type.js compares hash(code_verifier) to stored codeChallenge without validating verifier format/length.
  3. In AuthorizationCodeGrantType.handle, authorization code revocation happens after verifier validation. Invalid guesses fail before revoke, so the same code can be retried repeatedly.

Steps to Reproduce

Setup

  • PKCE authorization code exists with:
    • codeChallengeMethod = "S256"
    • codeChallenge = BASE64URL(SHA256("z")) (verifier is one character, RFC-invalid)
  • Attacker has intercepted the authorization code value.

Reproduction

  1. Send repeated token requests with guessed code_verifier values:
POST /token HTTP/1.1
Host: oauth.example
Content-Type: application/x-www-form-urlencoded

grant_type=authorization_code&
client_id=client1&
client_secret=s3cret&
code=stolen-auth-code&
redirect_uri=https://client.example/callback&
code_verifier=<guess>
  1. Observe invalid guesses return invalid_grant.
  2. Continue guessing (a..z).
  3. When code_verifier=z, token issuance succeeds and returns bearer tokens.

Confirmed PoC output

BRUTE_FORCE_SUCCESS { tries: 26, guess: 'z', status: 200, tokenIssued: true }

Impact

An intercepted authorization code can be redeemed by brute-forcing low-entropy verifiers that the server should have rejected under RFC7636.
This weakens PKCE’s protection goal and allows token theft when clients generate short/predictable verifiers.

Recommended Fix

  1. Enforce pkce.codeChallengeMatchesABNF(request.body.code_verifier) in authorization code token exchange before hashing/comparison.
  2. Reject verifier values outside RFC7636 charset/length (43..128 unreserved).
  3. Invalidate authorization codes on failed verifier attempts (or add strict retry limits) to prevent online guessing.

Affected Packages

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
📦npm@node-oauth/oauth2-serverall versions5.3.0npm install @node-oauth/oauth2-server@5.3.0

Affected Products

1 product · 1 configurations
Application
node-oauth\/oauth2-servernode-oauth
< 5.3.0
range

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for @node-oauth/oauth2-server, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update @node-oauth/oauth2-server to 5.3.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-41213 is resolved across your whole dependency graph.

  3. Workarounds

    If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Frequently Asked Questions

## Summary 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. ### Root cause 1. `lib/pkce/pkce.js` (`getHashForCodeChallenge`) only checks that `verifier` is a non-empty string before hashing for `S256`; it does not enforce RFC7636 ABNF (`43..128` unreserved chars). 2. `lib/gran
O3 Security · Impact-Aware SCA

Is CVE-2026-41213 in your dependencies?

Find it across npm, including transitive dependencies.

Scan my dependencies How O3 SCA works
CVE-2026-41213: @node-oauth/oauth2 — Fixed in 5.3.0