Bug 2448182 (CVE-2026-28498)

Summary:	CVE-2026-28498 authlib: Authlib: Authentication bypass via forged OpenID Connect ID Tokens
Product:	[Other] Security Response	Reporter:	OSIDB Bzimport <bzimport>
Component:	vulnerability	Assignee:	Product Security DevOps Team <prodsec-dev>
Status:	NEW ---	QA Contact:
Severity:	high	Docs Contact:
Priority:	high
Version:	unspecified	CC:	anthomas, bdettelb, dfreiber, doconnor, drow, dschmidt, ebourniv, ehelms, erezende, ggainey, hasun, jburrell, jkoehler, jlanda, juwatts, jwong, kshier, lgallett, lphiri, mhulan, nmoumoul, nyancey, omaciel, osousa, pcreech, ptisnovs, rchan, sbunciak, simaishi, smallamp, smcdonal, stcannon, teagle, tmalecek, ttakamiy, vkumar, yguenane
Target Milestone:	---	Keywords:	Security
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Hardware:	All
OS:	Linux
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Doc Text:	A flaw was found in Authlib, a Python library used for building OAuth and OpenID Connect (OIDC) servers. This vulnerability allows a remote attacker to bypass critical integrity checks in OIDC ID Tokens. Specifically, the library's internal hash verification logic fails open when encountering an unsupported cryptographic algorithm, accepting a forged ID Token as valid. This can lead to an authentication bypass, granting unauthorized access to systems relying on Authlib for OIDC authentication.	Story Points:	---
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oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
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Description OSIDB Bzimport 2026-03-16 19:02:24 UTC

Authlib is a Python library which builds OAuth and OpenID Connect servers. Prior to version 1.6.9, a library-level vulnerability was identified in the Authlib Python library concerning the validation of OpenID Connect (OIDC) ID Tokens. Specifically, the internal hash verification logic (_verify_hash) responsible for validating the at_hash (Access Token Hash) and c_hash (Authorization Code Hash) claims exhibits a fail-open behavior when encountering an unsupported or unknown cryptographic algorithm. This flaw allows an attacker to bypass mandatory integrity protections by supplying a forged ID Token with a deliberately unrecognized alg header parameter. The library intercepts the unsupported state and silently returns True (validation passed), inherently violating fundamental cryptographic design principles and direct OIDC specifications. This issue has been patched in version 1.6.9.