Critical Security Update: Apache2-mod_auth_openidc Vulnerability Patched (CVE-2025-3891)

  

SUSE releases an urgent security patch for Apache2-mod_auth_openidc (CVE-2025-3891) to fix a high-risk denial-of-service flaw. Learn how to protect your enterprise Linux systems with this critical update.

Overview of the Vulnerability

A severe security flaw (CVE-2025-3891) has been discovered in apache2-mod_auth_openidc, a critical authentication module for Apache web servers. 

Rated 8.2 CVSS (v4.0) by SUSE and 7.5 CVSS (v3.1) by NVD, this vulnerability allows attackers to trigger a denial-of-service (DoS) attack via an empty POST request when OIDCPreservePost is enabled.

Affected Systems Include:

• SUSE Linux Enterprise Server 15 SP6/SP7

• SUSE Linux Enterprise Real Time 15 SP6/SP7

• openSUSE Leap 15.6

• Server Applications Module 15-SP6/SP7

Why This Update Matters for Enterprise Security

1. High-Risk Exploit Potential

• Attack Vector: Remote (AV:N)

• Impact: Service disruption (VA:H)

• Zero User Interaction Required (UI:N)

This vulnerability poses a significant threat to enterprise web applications, particularly those handling sensitive authentication workflows.

2. Patch Availability & Installation Guide

SUSE has released an urgent security update to mitigate this risk. Below are the recommended patching methods:

For SUSE Linux Enterprise & openSUSE Systems

bash

Copy

Download

# Server Applications Module 15-SP6  
zypper in -t patch SUSE-SLE-Module-Server-Applications-15-SP6-2025-1953=1  

# Server Applications Module 15-SP7  
zypper in -t patch SUSE-SLE-Module-Server-Applications-15-SP7-2025-1953=1  

# openSUSE Leap 15.6  
zypper in -t patch SUSE-2025-1953=1 openSUSE-SLE-15.6-2025-1953=1  

Alternative Methods

• Use YaST Online Update for automated patching.

• Enterprise users should deploy via SUSE Manager for centralized control.

Technical Breakdown of CVE-2025-3891

Metric	Score (CVSS v4.0)	Score (CVSS v3.1)
Attack Vector	Network (AV:N)	Network (AV:N)
Impact	High Availability Loss (VA:H)	High Availability Impact (A:H)
Exploitability	Low Complexity (AC:L)	Low Complexity (AC:L)

Key Takeaway: This flaw is remotely exploitable and can crash Apache services, making it a priority for sysadmins.

Best Practices for Mitigation

1. Immediate Patching: Apply updates within 24 hours for critical systems.

2. Disable OIDCPreservePost if not required (temporary workaround).

3. Monitor Traffic for unusual POST requests.

FAQ: Apache2-mod_auth_openidc Security Update

Q: Is this vulnerability being actively exploited?

A: No confirmed exploits yet, but due to its high CVSS score, rapid patching is advised.

Q: Does this affect non-SUSE Linux distributions?

A: Only if they use a vulnerable version of mod_auth_openidc. Check with your vendor.

Q: What’s the business impact of this flaw?

A: Unpatched systems risk downtime, compliance violations, and potential data breaches.