{"dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": {"cveId": "CVE-2026-87853", "assignerOrgId": "53f830b8-0a3f-465b-8143-3b8a9948e749", "state": "PUBLISHED", "assignerShortName": "redhat", "dateReserved": "2026-09-09T13:00:35.698Z", "datePublished": "2026-09-09T16:06:25.638Z", "dateUpdated": "2026-09-09T16:06:25.638Z"}, "containers": {"cna": {"title": "Sssd: sssd: idp authentication prefix comparison allows cross-user impersonation", "metrics": [{"other": {"content": {"value": "Moderate", "namespace": "https://access.redhat.com/security/updates/classification/"}, "type": "Red Hat severity rating"}}, {"cvssV3_1": {"attackComplexity": "HIGH", "attackVector": "NETWORK", "availabilityImpact": "HIGH", "baseScore": 7.5, "baseSeverity": "HIGH", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "privilegesRequired": "LOW", "scope": "UNCHANGED", "userInteraction": "NONE", "vectorString": "CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H", "version": "3.1"}, "format": "CVSS"}], "descriptions": [{"lang": "en", "value": "A flaw was found in SSSD's IdP authentication provider. The eval_access_token_buf() function compares the OIDC subject identifier using strncmp() with the authenticated user's identifier length, performing a prefix comparison instead of an exact match. An attacker whose IdP identifier is a strict prefix of a target user's identifier can authenticate as the target user."}], "affected": [{"vendor": "Red Hat", "product": "Red Hat Enterprise Linux 10", "collectionURL": "https://access.redhat.com/downloads/content/package-browser/", "packageName": "sssd", "defaultStatus": "affected", "cpes": ["cpe:/o:redhat:enterprise_linux:10"]}, {"vendor": "Red Hat", "product": "Red Hat Enterprise Linux 6", "collectionURL": "https://access.redhat.com/downloads/content/package-browser/", "packageName": "sssd", "defaultStatus": "unknown", "cpes": ["cpe:/o:redhat:enterprise_linux:6"]}, {"vendor": "Red Hat", "product": "Red Hat Enterprise Linux 7", "collectionURL": "https://access.redhat.com/downloads/content/package-browser/", "packageName": "sssd", "defaultStatus": "unaffected", "cpes": ["cpe:/o:redhat:enterprise_linux:7"]}, {"vendor": "Red Hat", "product": "Red Hat Enterprise Linux 8", "collectionURL": "https://access.redhat.com/downloads/content/package-browser/", "packageName": "sssd", "defaultStatus": "unaffected", "cpes": ["cpe:/o:redhat:enterprise_linux:8"]}, {"vendor": "Red Hat", "product": "Red Hat Enterprise Linux 9", "collectionURL": "https://access.redhat.com/downloads/content/package-browser/", "packageName": "sssd", "defaultStatus": "unaffected", "cpes": ["cpe:/o:redhat:enterprise_linux:9"]}, {"vendor": "Red Hat", "product": "Red Hat OpenShift Container Platform 4", "collectionURL": "https://access.redhat.com/downloads/content/package-browser/", "packageName": "openshift/ose-rhel-coreos-8", "defaultStatus": "unaffected", "cpes": ["cpe:/a:redhat:openshift:4"]}, {"vendor": "Red Hat", "product": "Red Hat OpenShift Container Platform 4", "collectionURL": "https://access.redhat.com/downloads/content/package-browser/", "packageName": "openshift/ose-rhel-coreos-9", "defaultStatus": "unaffected", "cpes": ["cpe:/a:redhat:openshift:4"]}], "references": [{"url": "https://access.redhat.com/security/cve/CVE-2026-87853", "tags": ["vdb-entry", "x_refsource_REDHAT"]}, {"url": "https://bugzilla.redhat.com/show_bug.cgi?id=2530888", "name": "RHBZ#2530888", "tags": ["issue-tracking", "x_refsource_REDHAT"]}], "datePublic": "2026-09-09T14:15:45.513Z", "problemTypes": [{"descriptions": [{"cweId": "CWE-187", "description": "Partial String Comparison", "lang": "en", "type": "CWE"}]}], "x_redhatCweChain": "CWE-187: Partial String Comparison", "workarounds": [{"lang": "en", "value": "Deployments not using the IdP authentication provider (idp_type = keycloak) are not affected. For affected deployments: (1) If using Keycloak LDAP federation, switching to Import Users: enabled mode causes Keycloak to assign random UUIDs as sub claims, making prefix collisions astronomically unlikely. (2) Restrict PAM login to specific users via simple_allow_users or access_provider = simple. (3) Disable Keycloak self-registration to prevent attackers from creating accounts with chosen prefix usernames."}], "timeline": [{"lang": "en", "time": "2026-09-06T00:00:00.000Z", "value": "Reported to Red Hat."}, {"lang": "en", "time": "2026-09-09T14:15:45.513Z", "value": "Made public."}], "credits": [{"lang": "en", "value": "Red Hat would like to thank Moritz Theile for reporting this issue."}], "providerMetadata": {"orgId": "53f830b8-0a3f-465b-8143-3b8a9948e749", "shortName": "redhat", "dateUpdated": "2026-09-09T16:06:25.638Z"}, "x_generator": {"engine": "cvelib 1.8.0"}}}}

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