CVE-2023-3758: Fedoraproject SSSD Race Condition Flaw

CVE-2023-3758 Overview

CVE-2023-3758 is a race condition vulnerability discovered in SSSD (System Security Services Daemon) that affects how Group Policy Object (GPO) policies are applied to authenticated users. This flaw causes GPO policies to be inconsistently enforced, potentially leading to improper authorization decisions that could grant or deny access to resources inappropriately.

SSSD is a widely deployed system daemon that provides access to identity and authentication providers for Linux systems, commonly used in enterprise environments integrated with Active Directory. The race condition occurs during the policy evaluation process, creating a window where authentication decisions may be made with incomplete or outdated policy information.

Critical Impact

Race condition in GPO policy enforcement may allow authenticated users to bypass access controls or be incorrectly denied access to resources, affecting enterprise authentication infrastructure.

Affected Products

• Fedoraproject SSSD (all versions)
• Red Hat Enterprise Linux 8.x and 9.x (including EUS variants)
• Red Hat CodeReady Linux Builder 8.x and 9.x
• Red Hat Virtualization Host 4.0
• Fedora 38, 39, and 40

Discovery Timeline

• April 18, 2024 - CVE-2023-3758 published to NVD
• November 3, 2025 - Last updated in NVD database

Technical Details for CVE-2023-3758

Vulnerability Analysis

The vulnerability exists within SSSD's handling of Group Policy Object (GPO) evaluation for authenticated users. When SSSD processes authentication requests for users subject to GPO policies, a race condition can occur between the time the policy is checked and when the access decision is enforced. This Time-of-Check Time-of-Use (TOCTOU) class vulnerability means that the security state observed during policy evaluation may not match the actual state when the authorization decision is applied.

In environments where SSSD is configured to enforce GPO-based access controls from Active Directory, this inconsistency can result in two concerning outcomes: users who should be denied access may be granted entry, or legitimate users may be incorrectly blocked from accessing resources they should have permission to use. The adjacent network attack vector indicates exploitation requires network proximity to the target system, while the requirement for low privileges suggests an attacker needs some level of authenticated access to trigger the race condition.

Root Cause

The root cause is a race condition (CWE-362) in SSSD's GPO policy evaluation code path. The vulnerability stems from improper synchronization between threads or processes handling authentication requests and those responsible for policy retrieval and caching. When multiple authentication events occur in rapid succession or when policy updates are being processed, the timing window between checking the GPO policy and applying the access decision creates an opportunity for inconsistent enforcement.

Attack Vector

The attack requires adjacent network access, meaning an attacker must be on the same network segment as the target system. The attacker needs low-privilege authenticated access to initiate authentication requests. By carefully timing authentication attempts during policy transition periods or by generating concurrent authentication requests, an attacker can exploit the race window to achieve unauthorized access. The attack complexity is high due to the precise timing required to successfully trigger the race condition.

The exploitation scenario typically involves:

1. An attacker with basic network access and low-privilege credentials identifies a system using SSSD with GPO integration
2. The attacker monitors for or triggers conditions that cause GPO policy updates or cache invalidation
3. During the race window, authentication requests are submitted to exploit the inconsistent policy state
4. Successful exploitation results in access being granted despite GPO policies that should deny it

Detection Methods for CVE-2023-3758

Indicators of Compromise

• Unexpected successful authentication events for users who should be restricted by GPO policies
• Authentication log entries showing inconsistent access decisions for the same user in short time intervals
• SSSD debug logs indicating policy evaluation errors or timing-related warnings
• Anomalous patterns of repeated authentication attempts from the same source in rapid succession

Detection Strategies

• Enable verbose SSSD logging (debug_level = 6 or higher) to capture detailed GPO evaluation timing
• Implement authentication monitoring to detect users accessing resources that GPO policies should restrict
• Configure SIEM rules to alert on authentication patterns that indicate race condition exploitation attempts
• Monitor for rapid successive authentication events from the same user or source

Monitoring Recommendations

• Review SSSD logs regularly for GPO policy application failures or warnings
• Implement alerting on authentication anomalies where users gain access to restricted resources
• Monitor Active Directory security event logs for corresponding authentication events
• Track SSSD process restarts and cache refresh events as potential exploitation windows

How to Mitigate CVE-2023-3758

Immediate Actions Required

• Update SSSD to the latest patched version available from your distribution's package repository
• Review authentication logs to identify any potential exploitation of this vulnerability
• Consider temporarily increasing GPO cache timeout values to reduce race condition windows
• Audit current access patterns to identify any users who may have gained unauthorized access

Patch Information

Red Hat has released multiple security advisories addressing this vulnerability across their product portfolio. The fix is available through the following advisories:

• RHSA-2024:1919 - Red Hat Enterprise Linux 9
• RHSA-2024:1920 - Red Hat Enterprise Linux 8
• RHSA-2024:1921 - Red Hat Enterprise Linux 9.2 EUS
• RHSA-2024:1922 - Red Hat Enterprise Linux 8.8 EUS
• RHSA-2024:2571 - Red Hat Enterprise Linux 9.0 EUS
• RHSA-2024:3270 - Red Hat Virtualization Host

Fedora users should apply updates from the Fedora package repositories. The upstream fix is available via GitHub SSSD Pull Request #7302.

Workarounds

• If immediate patching is not possible, consider implementing additional access controls at the application or network layer
• Increase SSSD cache timeouts to reduce the frequency of policy refresh operations
• Monitor authentication logs closely for any signs of exploitation until patches can be applied
• Consider implementing network segmentation to limit adjacent network attack surface

# Verify SSSD version and check for available updates
sssd --version
dnf check-update sssd

# Apply security updates on RHEL/CentOS/Fedora
sudo dnf update sssd

# Restart SSSD after updating
sudo systemctl restart sssd

# Verify GPO settings in SSSD configuration
grep -i gpo /etc/sssd/sssd.conf