EUVD-2026-75084
GHSA-993g-jgf7-rg3x
Severity by source
AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
Network vector for OIDC token exchange; AC:H for required prefix-matching IdP sub claim; PR:L for mandatory valid IdP credential; full impact on impersonated account.
Primary rating from Vendor (redhat).
CVSS VectorVendor: redhat
Lifecycle Timeline
4DescriptionCVE.org
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.
AnalysisAI
Authentication bypass in SSSD's OIDC/IdP provider allows an authenticated IdP user whose subject identifier is a strict lexical prefix of a target user's identifier to impersonate that target user on SSSD-protected Linux systems. The root cause is eval_access_token_buf() passing the attacker-controlled identifier's length to strncmp(), reducing an identity equality check to a prefix test. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | The target system must be running SSSD with the IdP/OIDC authentication provider explicitly configured (`id_provider = oidc` or equivalent in `sssd.conf`) - this is not the default SSSD configuration, which uses `ldap` or `ad`. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The CVSS 7.5 vector (AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H) is internally consistent and well-calibrated: AC:H reflects the genuine prerequisite that the attacker must possess an IdP-registered identity whose `sub` claim is a strict prefix of the target's, requiring both advance knowledge of the target's identifier and the ability to register a matching prefix account. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | Full exploit scenario with step-by-step reproduction available after sign-in. |
| Remediation | Apply the SSSD package update distributed by Red Hat for the applicable RHEL version or OpenShift 4 release using `dnf update sssd` (RHEL 8/9/10) or `yum update sssd` (RHEL 6/7); consult https://access.redhat.com/security/cve/CVE-2026-87853 for the specific advisory RHSA number and confirmed fixed package version, as no exact version is independently confirmed in the available data. … Detailed patch versions, workarounds, and compensating controls in full report. |
Recommended ActionAI
Within 24 hours, identify all Red Hat Enterprise Linux and OpenShift systems with SSSD OIDC authentication enabled to establish exposure scope. …
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External POC / Exploit Code
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