Bug 2429869 (CVE-2026-0976)

Summary: CVE-2026-0976 org.keycloak/keycloak-quarkus-server: Keycloak: Proxy bypass due to improper handling of matrix parameters in URL paths
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: low Docs Contact:
Priority: low    
Version: unspecifiedCC: aschwart, asoldano, bbaranow, bmaxwell, boliveir, brian.stansberry, darran.lofthouse, dosoudil, istudens, ivassile, iweiss, mosmerov, mposolda, msvehla, nwallace, pberan, pesilva, pjindal, pmackay, rmartinc, rstancel, smaestri, ssilvert, sthorger, tom.jenkinson, vmuzikar
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in Keycloak. This improper input validation vulnerability occurs because Keycloak accepts RFC-compliant matrix parameters in URL path segments, while common reverse proxy configurations may ignore or mishandle them. A remote attacker can craft requests to mask path segments, potentially bypassing proxy-level path filtering. This could expose administrative or sensitive endpoints that operators believe are not externally reachable.
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Description OSIDB Bzimport 2026-01-15 07:10:16 UTC 
Improper input validation vulnerability in Keycloak related to the handling of matrix parameters in URL paths. The issue occurs because Keycloak, via its JAX-RS routing layer, accepts RFC-compliant matrix parameters (e.g., ;param) in path segments, while common reverse proxy configurations may ignore or mishandle them when enforcing access restrictions. A remote attacker can craft requests such as /realms;abc/master/account to mask path segments and bypass proxy-level path filtering. Although authentication is still required, this may expose administrative or sensitive endpoints that operators believe are not externally reachable. Exploitation is network-based, requires no authentication, and depends on the reverse proxy configuration in front of Keycloak.