Vulnerability in fast-jwt (CVE-2026-44351)
Summary
Vulnerability in fast-jwt (CVE-2026-44351). Confidential information can be exposed externally. Exploitable via Buffer. Mitigation: upgrade to 6.2.4 or later.
Original description
The description as published by the source.
fast-jwt provides fast JSON Web Token (JWT) implementation. Prior to 6.2.4, a critical authentication-bypass vulnerability in fast-jwt's async key-resolver flow allows any unauthenticated attacker to forge arbitrary JWTs that are accepted as authentic. When the application's key resolver returns an empty string (''), for example via the common keys[decoded.header.kid] || '' JWKS-style fallback, fast-jwt converts it to a zero-length Buffer, hands it to crypto.createSecretKey, derives allowedAlgorithms = ['HS256','HS384','HS512'] from it, and then verifies the token's signature against an empty-key HMAC. The attacker simply computes HMAC-SHA256(key='', input='${header}.${payload}'), which Node accepts without complaint — and the verifier returns the attacker-chosen payload (sub, admin, scopes, etc.) as authentic. This vulnerability is fixed in 6.2.4.
Source: NIST National Vulnerability Database 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-2026-44351 has been found in fast-jwt.
Attackers can target a specific entry point like Buffer over the network to misuse the product.
Confidential information can be exposed externally. CVSS score: 9.1/10.
What to do: upgrade fast-jwt to 6.2.4 or later.
If unsure, ask your IT team or search "fast-jwt CVE-2026-44351" on the vendor's site.
CVE-2026-44351 (fast-jwt) — CWE-1391 / CVSS v3 9.1
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: Buffer / crypto.createSecretKey / prepareKeyOrSecret / verifySignature
Patched: 6.2.4 — 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-1391) exists in fast-jwt. Attackers reach the vulnerable code path via Buffer without authentication.
Check the vendor advisory for the affected versions of fast-jwt. Attack surface: Buffer / crypto.createSecretKey / prepareKeyOrSecret / verifySignature.
Severity: Critical (CVSS 9.1/10). Confidential information can be exposed externally.
Update to 6.2.4.
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 6.2.4ステージング環境で 6.2.4 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
- advisory github.com
- advisory nvd.nist.gov
- advisory github.com
- package github.com
- web github.com