Vulnerability in fast-jwt (CVE-2026-107724)
Summary
Vulnerability in fast-jwt (CVE-2026-107724). Confidential information can be exposed externally. Mitigation: upgrade to 6.3.0 or later.
Original description
The description as published by the source.
Summary
fast-jwt 6.2.4 silently classifies raw serialized public JWK JSON
as an HMAC secret.
If an application supplies public JWK JSON text as the verifier key and
HS256 is explicitly allowed or automatically inferred, an attacker who
knows the same public JSON text can use it as an HMAC key and create an
arbitrary HS256 token that fast-jwt accepts as valid.
This can result in authentication or authorization bypass through forged
JWT claims.
The PoC demonstrates the issue with a serialized RSA public JWK. The same
non-PEM classification also applies to raw JWKS JSON text, although the
attached standalone PoC focuses on the smallest JWK case.
Details
The verifier accepts a string or Buffer as key material. In
src/crypto.js, performDetectPublicKeyAlgorithms() attempts to infer
the permitted algorithm family from the supplied string.
Strings matching supported PEM public-key formats are classified as
asymmetric keys. Any other non-empty string is assumed to be an HMAC
secret:
function performDetectPublicKeyAlgorithms(key) {
const trimmedKey = key.trim()
const publicKeyPemMatch = trimmedKey.match(publicKeyPemMatcher)
if (trimmedKey.match(privateKeyPemMatcher)) {
throw new TokenError(
TokenError.codes.invalidKey,
'Private keys are not supported for verifying.'
)
} else if (
publicKeyPemMatch &&
publicKeyPemMatch[1] === 'RSA'
) {
return rsaAlgorithms
} else if (
!publicKeyPemMatch &&
!trimmedKey.inc…
Source: GitHub Security Advisories (Global) NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-107724 has been found in fast-jwt.
Confidential information can be exposed externally. CVSS score: 7.4/10.
What to do: upgrade fast-jwt to 6.3.0 or later.
If unsure, ask your IT team or search "fast-jwt CVE-2026-107724" on the vendor's site.
CVE-2026-107724 (fast-jwt) — CWE-347 / CVSS v3 7.4
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Patched: 6.3.0 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
A vulnerability (CWE-347) exists in fast-jwt.
Check the vendor advisory for the affected versions of fast-jwt.
Severity: High (CVSS 7.4/10). Confidential information can be exposed externally.
Update to 6.3.0.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'fast-jwt' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
-
1Identify exposure identify
grep -r 'fast-jwt' . | grep -v node_modulesリポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で
fast-jwtを grep し、稼働しているサービス・バージョンを把握する。 -
2Apply patch patch
Upgrade fast-jwt to 6.3.0ステージング環境で 6.3.0 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。
-
3Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。
Affected packages
References
- package github.com
- web github.com
- web github.com
- web github.com
- web github.com
- web github.com