CVE-2026-92821: SSSD Authentication Bypass Vulnerability

CVE-2026-92821 Overview

A flaw in the System Security Services Daemon (SSSD) allows authenticated users with expired passwords to bypass Lightweight Directory Access Protocol (LDAP) access control rules. When SSSD evaluates password expiration warnings before restrictive access rules, the warning terminates rule evaluation early. The access request is then treated as successful.

Remote authenticated users can exploit this flaw when using alternative authentication methods such as SSH public key authentication. The bypass grants unauthorized access to protected systems that should otherwise reject the session based on LDAP access rules.

Critical Impact
Authenticated users with expired credentials can bypass LDAP access control restrictions and reach systems they are not authorized to use, undermining identity-based segmentation.

Affected Products

SSSD (System Security Services Daemon) in LDAP-integrated environments
Red Hat Enterprise Linux deployments using SSSD with LDAP access control providers
Linux systems configured to evaluate password expiration warnings before access rule enforcement

Discovery Timeline

2026-10-06 - CVE-2026-92821 published to the National Vulnerability Database
2026-10-06 - Last updated in NVD database

Technical Details for CVE-2026-92821

Vulnerability Analysis

The flaw is a logic error in SSSD's access control evaluation pipeline, classified under [CWE-393] Return of Wrong Status Code. SSSD coordinates authentication and authorization against LDAP directories on Linux hosts. When password expiration warnings are evaluated before restrictive access rules, the warning path short-circuits further rule evaluation.

The daemon returns a success status to the calling authentication module. The result is a workflow bypass where the authorization decision never reflects the restrictive LDAP rules intended by the administrator. This defeats the purpose of host-based access control (HBAC) and group-based LDAP filters.

The impact is amplified when password-independent authentication methods are in use. SSH public key authentication, for example, does not require the expired password, so the user successfully authenticates while the authorization layer incorrectly green-lights the session.

Root Cause

The root cause is an ordering defect in SSSD's access provider logic. The password expiration warning handler returns an early success status rather than continuing evaluation of subsequent access rules. Rule evaluation should be deterministic and process all restrictive constraints before any status is returned.

Attack Vector

An attacker needs valid LDAP account credentials with an expired password and an alternative authentication method such as a registered SSH public key. The attacker initiates an authenticated session to a target host managed by SSSD. SSSD processes the expiration warning first, returns success, and skips the restrictive access rule that would normally deny the session. The attacker gains shell access to a system outside their authorized scope.

No exploit code is required. The vulnerability manifests through normal authentication flows. See the Red Hat CVE-2026-92821 advisory and Red Hat Bug Report #2479031 for upstream analysis.

Detection Methods for CVE-2026-92821

Indicators of Compromise

Successful SSH logins from accounts with expired LDAP passwords recorded in /var/log/secure or journalctl -u sshd
SSSD debug logs in /var/log/sssd/ showing access-granted decisions immediately following password expiration warnings
Session activity from user accounts on hosts where LDAP access rules should have denied the login

Detection Strategies

Correlate pam_sss success events with LDAP shadowExpire or pwdChangedTime attributes to flag logins by expired-password accounts
Enable SSSD debug logging at level 7 and search for access control evaluations that terminate after the expiration warning stage
Audit SSH authentication events for public key logins by users whose directory records indicate expired credentials

Monitoring Recommendations

Centralize sssd, sshd, and PAM logs in a SIEM and build alerts on expired-password authentication success events
Monitor directory server logs for bind operations followed by host sessions that should have been rejected by HBAC rules
Review access control rule hit rates on managed hosts to detect anomalies consistent with early termination of rule evaluation

How to Mitigate CVE-2026-92821

Immediate Actions Required

Apply vendor-supplied SSSD updates once available from your Linux distribution
Audit SSSD configuration for access providers that evaluate password warnings before restrictive rules
Force password resets for LDAP accounts currently flagged as expired to remove the exploitation precondition
Review authorized SSH public keys for accounts with expired credentials and revoke keys that are no longer needed

Patch Information

Refer to the Red Hat CVE-2026-92821 advisory for distribution-specific patched package versions. Track upstream SSSD release notes for the fixed version and deploy updates through your standard package management process. Validate that the fix enforces complete rule evaluation regardless of password expiration state.

Workarounds

Disable SSH public key authentication for accounts governed by LDAP access control until patches are deployed
Reconfigure SSSD so restrictive access rules are evaluated before password expiration warnings
Enforce short password expiration enforcement grace periods and lock expired accounts at the directory level
Restrict host access through firewall rules or jump-host architectures while remediation is in progress

bash

# Configuration example: ensure LDAP access provider enforces rules
# /etc/sssd/sssd.conf
[domain/example.com]
access_provider = ldap
ldap_access_order = filter, expire
ldap_access_filter = (memberOf=cn=allowed_users,ou=groups,dc=example,dc=com)
# Lock expired accounts at the directory to prevent bypass
ldap_pwd_policy = shadow