CVE-2026-28498 (GCVE-0-2026-28498)

Vulnerability from cvelistv5 – Published: 2026-03-16 18:03 – Updated: 2026-07-01 12:04
VLAI
Title
Authlib: Fail-Open Cryptographic Verification in OIDC Hash Binding
Summary
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.
Severity
8.2 (High)
CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N
9.1 (Critical)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
SSVC
Exploitation: poc Automatable: no Technical Impact: partial
CISA Coordinator (v2.0.3)
CWE
  • CWE-354 - Improper Validation of Integrity Check Value
  • CWE-573 - Improper Following of Specification by Caller
  • CWE-325 - Missing Cryptographic Step
Assigner
References
Impacted products
Show details on NVD website
To clipboard 

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      "cve": "CVE-2026-28498",
      "id": "CVE-2026-28498",
      "initial_release_date": "2026-03-16T18:03:28.821000+00:00",
      "product_status:fixed": "22",
      "product_status:known_affected": "2",
      "product_status:known_not_affected": "216",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "authlib: Authlib: Authentication bypass via forged OpenID Connect ID Tokens",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-28498.json",
      "version": "3"
    },
    "vulnrichment": {
      "containers": "{\"adp\": [{\"title\": \"CISA ADP Vulnrichment\", \"metrics\": [{\"other\": {\"type\": \"ssvc\", \"content\": {\"id\": \"CVE-2026-28498\", \"role\": \"CISA Coordinator\", \"options\": [{\"Exploitation\": \"poc\"}, {\"Automatable\": \"no\"}, {\"Technical Impact\": \"partial\"}], \"version\": \"2.0.3\", \"timestamp\": \"2026-03-16T18:14:21.039703Z\"}}}], \"providerMetadata\": {\"orgId\": \"134c704f-9b21-4f2e-91b3-4a467353bcc0\", \"shortName\": \"CISA-ADP\", \"dateUpdated\": \"2026-03-16T18:14:33.935Z\"}}], \"cna\": {\"title\": \"Authlib: Fail-Open Cryptographic Verification in OIDC Hash Binding\", \"source\": {\"advisory\": \"GHSA-m344-f55w-2m6j\", \"discovery\": \"UNKNOWN\"}, \"metrics\": [{\"cvssV4_0\": {\"version\": \"4.0\", \"baseScore\": 8.2, \"attackVector\": \"NETWORK\", \"baseSeverity\": \"HIGH\", \"vectorString\": \"CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N\", \"userInteraction\": \"NONE\", \"attackComplexity\": \"HIGH\", \"attackRequirements\": \"PRESENT\", \"privilegesRequired\": \"NONE\", \"subIntegrityImpact\": \"NONE\", \"vulnIntegrityImpact\": \"HIGH\", \"subAvailabilityImpact\": \"NONE\", \"vulnAvailabilityImpact\": \"NONE\", \"subConfidentialityImpact\": \"NONE\", \"vulnConfidentialityImpact\": \"NONE\"}}], \"affected\": [{\"vendor\": \"authlib\", \"product\": \"authlib\", \"versions\": [{\"status\": \"affected\", \"version\": \"\u003c 1.6.9\"}]}], \"references\": [{\"url\": \"https://github.com/authlib/authlib/security/advisories/GHSA-m344-f55w-2m6j\", \"name\": \"https://github.com/authlib/authlib/security/advisories/GHSA-m344-f55w-2m6j\", \"tags\": [\"x_refsource_CONFIRM\"]}, {\"url\": \"https://github.com/authlib/authlib/commit/b9bb2b25bf8b7e01512d847a95c1749646eaa72b\", \"name\": \"https://github.com/authlib/authlib/commit/b9bb2b25bf8b7e01512d847a95c1749646eaa72b\", \"tags\": [\"x_refsource_MISC\"]}, {\"url\": \"https://github.com/authlib/authlib/releases/tag/v1.6.9\", \"name\": \"https://github.com/authlib/authlib/releases/tag/v1.6.9\", \"tags\": [\"x_refsource_MISC\"]}], \"descriptions\": [{\"lang\": \"en\", \"value\": \"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.\"}], \"problemTypes\": [{\"descriptions\": [{\"lang\": \"en\", \"type\": \"CWE\", \"cweId\": \"CWE-354\", \"description\": \"CWE-354: Improper Validation of Integrity Check Value\"}]}, {\"descriptions\": [{\"lang\": \"en\", \"type\": \"CWE\", \"cweId\": \"CWE-573\", \"description\": \"CWE-573: Improper Following of Specification by Caller\"}]}], \"providerMetadata\": {\"orgId\": \"a0819718-46f1-4df5-94e2-005712e83aaa\", \"shortName\": \"GitHub_M\", \"dateUpdated\": \"2026-03-16T18:03:28.821Z\"}}}",
      "cveMetadata": "{\"cveId\": \"CVE-2026-28498\", \"state\": \"PUBLISHED\", \"dateUpdated\": \"2026-03-16T18:14:42.149Z\", \"dateReserved\": \"2026-02-27T20:57:47.708Z\", \"assignerOrgId\": \"a0819718-46f1-4df5-94e2-005712e83aaa\", \"datePublished\": \"2026-03-16T18:03:28.821Z\", \"assignerShortName\": \"GitHub_M\"}",
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}



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Taxonomy of the tags.





Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

Author Source Type Date Other

Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


Detection rules are retrieved from Rulezet.