CVE-2026-68743: SSSD PAM Responder DoS Vulnerability

CVE-2026-68743 Overview

CVE-2026-68743 is an out-of-bounds read vulnerability in the System Security Services Daemon (SSSD). The extract_authtok_v1() function in the PAM (Pluggable Authentication Module) responder fails to validate the auth_token_length field against the remaining buffer size before processing incoming data. A local attacker can send a crafted protocol v1 request to the PAM responder socket, triggering an out-of-bounds read and process crash. The result is a denial of service against the SSSD PAM responder. The flaw is classified under CWE-125 (Out-of-Bounds Read).

Critical Impact
Local attackers can crash the SSSD PAM responder, disrupting authentication services on affected Linux systems.

Affected Products

SSSD (System Security Services Daemon)
Red Hat Enterprise Linux distributions shipping affected SSSD versions
Linux distributions integrating SSSD for centralized authentication

Discovery Timeline

2026-08-04 - CVE-2026-68743 published to NVD
2026-08-06 - Last updated in NVD database

Technical Details for CVE-2026-68743

Vulnerability Analysis

SSSD provides access to remote identity and authentication providers on Linux systems. The PAM responder component handles authentication requests from PAM-enabled applications via a local Unix domain socket. The vulnerability resides in the extract_authtok_v1() function, which parses protocol version 1 authentication token structures.

The function reads an auth_token_length field from the incoming request but does not verify that this length falls within the remaining buffer boundaries. When the declared length exceeds the actual buffer size, subsequent read operations access memory beyond the allocated region. This out-of-bounds read triggers a process crash and terminates the PAM responder.

The attack requires local access with low privileges and no user interaction. Successful exploitation disrupts authentication services for all users and applications that depend on SSSD-mediated authentication.

Root Cause

The root cause is missing input validation in extract_authtok_v1(). The function trusts the attacker-controlled auth_token_length field without cross-checking it against the size of the received message. This omission violates safe parsing practices for length-prefixed binary protocols.

Attack Vector

A local attacker connects to the PAM responder Unix socket and submits a malformed protocol v1 request containing an oversized auth_token_length value. The PAM responder reads past the end of the request buffer, triggers undefined memory access, and crashes. Authentication requests routed through SSSD subsequently fail until the daemon restarts.

No verified public exploit code is available. See the Red Hat CVE-2026-68743 Advisory and Red Hat Bugzilla Report #2509760 for vendor technical details.

Detection Methods for CVE-2026-68743

Indicators of Compromise

Unexpected termination or repeated restarts of the sssd_pam process in system logs
Authentication failures across multiple services coincident with SSSD PAM responder crashes
Core dumps or systemd service failure entries referencing the SSSD PAM responder
Local processes connecting to the SSSD PAM socket with abnormal message patterns

Detection Strategies

Monitor systemd and journalctl output for sssd_pam service failures and abnormal exits
Audit local process activity that opens connections to /var/lib/sss/pipes/pam or related SSSD sockets
Correlate authentication service disruptions with local user activity to identify potential exploitation attempts

Monitoring Recommendations

Enable verbose SSSD logging via debug_level in sssd.conf to capture protocol parsing errors
Forward SSSD and PAM logs to a centralized log platform for correlation with endpoint telemetry
Alert on repeated SSSD PAM responder crashes within short time windows to flag likely abuse

How to Mitigate CVE-2026-68743

Immediate Actions Required

Apply vendor-supplied SSSD updates as soon as they become available from your Linux distribution
Restrict local user access on multi-user systems and enforce least privilege for shell accounts
Monitor the SSSD PAM responder service and configure automatic restart on failure via systemd

Patch Information

Red Hat is tracking this vulnerability in Red Hat Bugzilla Report #2509760. Refer to the Red Hat CVE-2026-68743 Advisory for fixed package versions and errata. Downstream Linux distributions will publish corresponding updates through their standard channels.

Workarounds

Limit interactive local access to trusted administrators until patched packages are deployed
Configure systemd to automatically restart sssd and sssd_pam on failure to reduce authentication downtime
Where feasible, restrict permissions on the SSSD PAM socket directory to reduce the local attack surface

bash

# Configure systemd to automatically restart the SSSD service on failure
sudo systemctl edit sssd.service

# Add the following override:
# [Service]
# Restart=always
# RestartSec=5

sudo systemctl daemon-reload
sudo systemctl restart sssd