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CVE-2026-102266— PyJWK accepts empty HMAC keys, bypassing PyJWT's empty-key validation

Quick assessment

Affected
jpadilla pyjwt
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.

PyJWT 是 JSON Web Token (JWT) 标准的 Python 实现。在版本 2.13.0 到 2.14.0 之间，HMACAlgorithm.from_jwk 方法存在安全漏洞，原因是 PyJWK 验证路径在未执行 prepare_key 验证的情况下直接使用了已解码的密钥。当受信任的 JWK Set 中包含一个 oct 类型的密钥，且其 k（密钥）字段为空值时，就会触发此问题。攻击者可以利用这一漏洞，使用与 PyJWT 接受的零长度密钥相同的密钥对 HMAC 令牌进行签名。因此，伪造的令牌可以携

CVSS 7.4 · High

Possible ATT&CK Techniques 1 AI

T1556.004 · Network Device Authentication
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I. Basic Information for CVE-2026-102266

Vulnerability Information
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Vulnerability Title
PyJWK accepts empty HMAC keys, bypassing PyJWT's empty-key validation
Source: CVE Program / CVE List V5
Vulnerability Description
PyJWT is a Python implementation of JSON Web Token standards. From 2.13.0 until 2.14.0, HMACAlgorithm.from_jwk is affected because PyJWK verification path used the decoded key without applying prepare_key validation. This occurs when a trusted JWK Set contains an oct entry with an empty k value. As a result, an attacker signs an HMAC token with the same zero-length key accepted by PyJWT. Consequently, forged token can carry arbitrary authenticated claims. This issue is fixed in version 2.14.0.
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
jpadilla pyjwt >= 2.13.0, < 2.14.0 -

II. Public POCs for CVE-2026-102266

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III. Intelligence Information for CVE-2026-102266

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Other References for CVE-2026-102266 (3)

Same Patch Batch · jpadilla · 2026-09-28 · 13 CVEs total

CVE-2026-102268 9.1 CRITICAL PyJWT: Asymmetric-PEM detection bypass: whitespace/line-ending-mutated public keys skip th
CVE-2026-102267 7.4 HIGH PyJWT: PyJWKClient follows redirects when fetching JWKS
CVE-2026-102271 7.4 HIGH PyJWT: Public keys in DER form are accepted as HMAC secrets, bypassing the CVE-2022-29217
CVE-2026-102272 7.4 HIGH PyJWT BOM Bypass
CVE-2026-102273 7.4 HIGH PyJWT accepts public JWK containers as HMAC secrets
CVE-2026-102275 6.5 MEDIUM PyJWT accepts inconsistent OKP x/d JWKs, causing public/private key identity confusion
CVE-2026-102274 5.9 MEDIUM PyJWT: Malformed RSA JWK aborts parsing of an entire JWK Set
CVE-2026-101918 5.3 MEDIUM PyJWT: Unauthenticated RecursionError DoS in pre-verification payload parse (PyJWKClient.g
CVE-2026-101917 5.3 MEDIUM PyJWT: PyJWKClient still amplifies unauthenticated JWKS fetches on unknown kid values (inc
CVE-2026-102265 5.3 MEDIUM PyJWT: Uncaught RecursionError in jwt.decode() on deeply nested token header
CVE-2026-102269 4.8 MEDIUM PyJWT: Non-canonical signature segments enable raw-token revocation bypass
CVE-2026-102270 4.4 MEDIUM PyJWT: ReDoS vulnerability when calling the `is_pem_format` function.

IV. Related Vulnerabilities

Same product: pyjwt
Same vendor: jpadilla
Same weakness: CWE-347

V. Comments for CVE-2026-102266

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