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CVE-2026-85394— python-jose through 3.5.0 Algorithm Confusion via DER-encoded Public Key as HMAC Secret

Quick assessment

Affected
mpdavis python-jose
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.

python-jose 在 3.5.0 及之前版本中，在 HMAC 初始化过程中未能正确验证非对称密钥，会接受缺少 PEM 头尾（armor）或 SSH 前缀的 DER 编码公钥。如果未显式限制算法，持有服务公钥的攻击者可以伪造能通过验证的 HS256 令牌。此问题是对 CVE-2024-33663 的不完整修复。

CVSS 9.1 · Critical

Affected Version Matrix 1

VendorProduct Version RangeStatus
mpdavis python-jose ≤ 3.5.0 affected
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I. Basic Information for CVE-2026-85394

Vulnerability Information
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Vulnerability Title
python-jose through 3.5.0 Algorithm Confusion via DER-encoded Public Key as HMAC Secret
Source: CVE Program / CVE List V5
Vulnerability Description
python-jose through 3.5.0 fails to properly validate asymmetric keys in HMAC initialization, accepting DER-encoded public keys that lack PEM armor or SSH prefixes. Attackers holding the service's public key can forge HS256 tokens that pass verification when algorithms are not explicitly restricted. This is an incomplete fix for CVE-2024-33663.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/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
mpdavis python-jose 0 ~ 3.5.0 -

II. Public POCs for CVE-2026-85394

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III. Intelligence Information for CVE-2026-85394

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Patches & Fixes for CVE-2026-85394 (1)

Vendor Advisories for CVE-2026-85394 (3)

Other References for CVE-2026-85394 (1)

IV. Related Vulnerabilities

Same weakness: CWE-347

V. Comments for CVE-2026-85394

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