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CVE-2026-107724— fast-jwt treats raw public JWK JSON as an HMAC secret, enabling HS256 token forgery

Quick assessment

Affected
nearform fast-jwt
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

fast-jwt 提供了高效的 JSON Web Token (JWT) 实现。在版本 6.2.4 中，fast-jwt 可能将原始序列化的公开 JWK 或 JWKS JSON 误识别为 HMAC 密钥，这是因为 src/crypto.js 中的 performDetectPublicKeyAlgorithms 函数将非 PEM 格式的字符串视为对称密钥材料。如果 HS256 算法被显式允许或被推断使用，攻击者可以利用已知的公开密钥序列化字节作为 HMAC 密钥，创建包含任意声明（claims）的令牌，而该令牌会被

CVSS 7.4 · High

Possible ATT&CK Techniques 1 AI

T1556 · Modify Authentication Process
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I. Basic Information for CVE-2026-107724

Vulnerability Information
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Vulnerability Title
fast-jwt treats raw public JWK JSON as an HMAC secret, enabling HS256 token forgery
Source: CVE Program / CVE List V5
Vulnerability Description
fast-jwt provides fast JSON Web Token (JWT) implementation. In 6.2.4, fast-jwt can classify raw serialized public JWK or JWKS JSON as an HMAC secret because src/crypto.js performDetectPublicKeyAlgorithms treats non-PEM strings as symmetric key material. If HS256 is explicitly allowed or inferred, an attacker who knows the exact serialized public-key bytes can use those bytes as an HMAC key and create a token containing arbitrary claims that createVerifier accepts. Serialization ordering or whitespace differences can prevent exploitation, and applications using supported PEM keys with an asymmetric-only algorithm allowlist are not affected. This issue is fixed in version 6.3.0.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
密码学签名的验证不恰当
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
nearform fast-jwt >= 6.2.4, < 6.3.0 -

II. Public POCs for CVE-2026-107724

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III. Intelligence Information for CVE-2026-107724

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Patches & Fixes for CVE-2026-107724 (2)

Vendor Advisories for CVE-2026-107724 (1)

Vendor Pages for CVE-2026-107724 (1)

Same Patch Batch · nearform · 2026-10-08 · 6 CVEs total

CVE-2026-107722 9.8 CRITICAL fast-jwt: Incomplete patch of CVE-2026-34950: Non-whitespace key-prefix re-enables RSA→HS2
CVE-2026-107723 8.1 HIGH fast-jwt : Silent claim-validator bypass when JWT payload is a JSON array
CVE-2026-107720 7.4 HIGH fast-jwt: createVerifier accepts unsigned JWTs when key is '' or null and algorithms is ex
CVE-2026-107721 5.9 MEDIUM fast-jwt clockTolerance: Infinity silently bypasses both exp and nbf validation (and persi
CVE-2026-107719 4.2 MEDIUM fast-jwt: Verifier cache accepts expired JWTs without iat.

IV. Related Vulnerabilities

Same product: fast-jwt
Same vendor: nearform
Same weakness: CWE-347

V. Comments for CVE-2026-107724

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