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CVE-2026-55165— Lemur : JWT verifier trusts attacker-supplied alg from token header — defense-in-depth gap; chain-dependent ATO with secret disclosure

Quick assessment

Affected
Netflix lemur
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.

Netflix lemur是美国Netflix公司开源的一个证书管理工具。 Netflix Lemur 1.9.2之前版本存在加密问题漏洞，该漏洞源于JWT验证器从未经验证的令牌中读取alg参数并传递给decode_with_multiple_secrets，导致算法未固定，可能通过算法混淆被利用，并削弱基于算法的异常检测。

CVSS 4.8 · Medium EPSS 0.15% · P4

Possible ATT&CK Techniques 1 AI

T1550.001 · Application Access Token

Affected Version Matrix 1

VendorProduct Version RangeStatus
Netflix lemur < 1.9.2 affected
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I. Basic Information for CVE-2026-55165

Vulnerability Information
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Vulnerability Title
Lemur : JWT verifier trusts attacker-supplied alg from token header — defense-in-depth gap; chain-dependent ATO with secret disclosure
Source: CVE Program / CVE List V5
Vulnerability Description
Lemur manages TLS certificate creation. Prior to 1.9.2, the JWT verifier in lemur/auth/service.py:130-137 used fetch_token_header to read header_data["alg"] from an unverified token and passed that attacker-controlled value to decode_with_multiple_secrets. PyJWT 2.x rejects alg=none with the configured key, so the flaw is a defense-in-depth gap rather than a direct authentication bypass in the shipped configuration. The unpinned algorithm can become exploitable after an asymmetric-signing migration through algorithm confusion, and it weakens algorithm-based anomaly detection because the token chooses the recorded value. A separate disclosure of LEMUR_TOKEN_SECRET would also permit forged HS256 tokens, although that disclosure is an independent prerequisite. The fix introduces the server-controlled LEMUR_TOKEN_ALGORITHMS allowlist and defaults it to HS256. This issue is fixed in version 1.9.2.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/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
Vulnerability Title
Netflix Lemur 加密问题漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Netflix lemur是美国Netflix公司开源的一个证书管理工具。 Netflix Lemur 1.9.2之前版本存在加密问题漏洞，该漏洞源于JWT验证器从未经验证的令牌中读取alg参数并传递给decode_with_multiple_secrets，导致算法未固定，可能通过算法混淆被利用，并削弱基于算法的异常检测。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
Netflix lemur < 1.9.2 -

II. Public POCs for CVE-2026-55165

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III. Intelligence Information for CVE-2026-55165

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Patches & Fixes for CVE-2026-55165 (1)

Vendor Advisories for CVE-2026-55165 (1)

Vendor Pages for CVE-2026-55165 (1)

Same Patch Batch · Netflix · 2026-08-18 · 14 CVEs total

CVE-2026-55166 9.9 CRITICAL Lemur: any SSO-authenticated user achieves AWS IAM compromise and permanent PKI key access
CVE-2026-48508 8.8 HIGH Lemur: Authorization bypass in StrictRolePermission / AuthorityCreatorPermission
CVE-2026-71308 8.1 HIGH Lemur: Unchecked `replaces[]` lets any user silence notifications and hijack auto-rotation
CVE-2026-71307 7.7 HIGH Lemur: Authenticated low-privilege users can read plaintext destination credentials (SFTP
CVE-2026-71303 7.7 HIGH Lemur: Incomplete fix for CVE-2026-55166 -- ACME authority update endpoint allows non-admi
CVE-2026-70666 7.4 HIGH Lemur: Server-Side Request Forgery via the ACME client following server-controlled URLs
CVE-2026-71417 7.3 HIGH Lemur: Any user can revoke arbitrary certificates at the CA by uploading a duplicate recor
CVE-2026-71317 6.5 MEDIUM Lemur: Sub-CA creation never checks `AuthorityPermission` on the parent authority
CVE-2026-70667 6.3 MEDIUM Lemur: SSRF protection in certificate revocation checking bypassable via HTTP redirects an
CVE-2026-55162 6.3 MEDIUM Lemur: Post-authentication SSRF via certificate verification - attacker-controlled CRL and
CVE-2026-55163 6.3 MEDIUM Lemur: Privilege escalation via PUT /api/1/roles/<id> — non-admin role members can rewrite
CVE-2026-55164 4.9 MEDIUM Lemur: Plaintext password storage in Lemur user-update path
CVE-2026-71322 4.3 MEDIUM Lemur: Missing authorization check on POST /certificates/<id>/export for plugins with requ

IV. Related Vulnerabilities

Same product: lemur
Same vendor: Netflix
Same weakness: CWE-347

V. Comments for CVE-2026-55165

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