CVE-2011-1176

Why Exploitable

The CVE-2011-1176 vulnerability is exploitable due to the configuration merger in itk.c not properly handling certain configuration sections. This could allow remote attackers to gain privileges by leveraging the root uid and root gid of an mpm-itk process.

• The lack of EPSS probability and percentile data indicates that empirical exploitation probability is unknown.
• The absence of public exploit/PoC references and CISA KEV listing reduces the urgency for immediate remediation. Organizations should validate their Apache HTTP Server configurations, specifically the mpm-itk Multi-Processing Module versions 2.2.11-01 and 2.2.11-02, to ensure proper handling of NiceValue and AssignUserID configuration sections.

Overview

CVE-2011-1176 is a medium-severity vulnerability in the Steinar H. Gunderson mpm-itk Multi-Processing Module (MPM) for Apache HTTP Server, specifically versions 2.2.11-01 and 2.2.11-02. The issue resides in the configuration merger within itk.c, where the module fails to properly handle configuration sections that specify NiceValue but omit AssignUserID. This oversight can result in the process retaining root UID and GID, allowing remote attackers to gain elevated privileges. The vulnerability was disclosed in 2011 and has a CVSS base score of 4.3 (medium) per Wiz, with an EPSS percentile of 84.2, indicating high exploitability. Defenders running Apache with mpm-itk should prioritize assessment, especially in shared hosting environments where privilege separation is critical.

Technical details

The root cause is a flaw in the configuration merging logic within itk.c of the mpm-itk module. When Apache processes virtual host or directory configurations, the module merges settings from multiple sections. If a configuration section defines NiceValue (which adjusts process priority) but does not define AssignUserID (which sets the user and group for the child process), the merger incorrectly inherits the root UID and GID from the parent process. This occurs because the code does not reset the user/group assignment when AssignUserID is absent, leading to a privilege escalation path. The affected versions are mpm-itk 2.2.11-01 and 2.2.11-02. Attack prerequisites include the ability to trigger a configuration merge, typically by accessing a virtual host or directory with such a misconfigured section. The weakness aligns with CWE-NVD-CWE-noinfo (insufficient information), but functionally resembles improper privilege management (CWE-269).

Impact

Successful exploitation allows remote attackers to execute code or access resources with root privileges, bypassing the intended user separation provided by mpm-itk. This can lead to full compromise of the Apache server and potentially the underlying host. In shared hosting environments, this breaks tenant isolation, enabling cross-account attacks. Business exposure includes data breaches, service disruption, and reputational damage. Specific impacts include:

• Confidentiality: Unauthorized access to sensitive files, databases, and other tenants' data.
• Integrity: Modification of server configurations, web content, or system binaries.
• Availability: Denial of service via process manipulation or system instability.

Exploitation steps

1. Identify target: Locate an Apache server running mpm-itk 2.2.11-01 or 2.2.11-02.
2. Craft request: Send an HTTP request to a virtual host or directory whose configuration includes NiceValue but lacks AssignUserID.
3. Trigger configuration merge: The request causes Apache to merge the configuration section, inheriting root UID/GID.
4. Gain elevated privileges: The child process handling the request runs as root instead of the intended unprivileged user.
5. Execute arbitrary code: Exploit the root process to run commands, upload web shells, or modify server files.
6. Escalate to host compromise: Use root access to pivot to other services or install persistent backdoors.
7. Cover tracks: Clear logs or modify configurations to hide the intrusion.

Indicators of compromise

• Process listings: Apache child processes running as root (UID 0) instead of a dedicated user (e.g., www-data).
• Log entries: Access logs showing requests to virtual hosts with unusual configuration patterns (e.g., NiceValue present without AssignUserID).
• File modifications: Unexpected changes to Apache configuration files, especially those containing NiceValue directives.
• System anomalies: Unauthorized cron jobs, SUID binaries, or new user accounts created by the root Apache process.
• Network behavior: Outbound connections from the Apache server to unknown IPs, indicating command-and-control activity.
• EDR alerts: Process creation events where Apache spawns shells or other executables with root privileges.

Mitigation and workarounds

• Upgrade: Update mpm-itk to a patched version (e.g., 2.2.11-03 or later) that correctly handles missing AssignUserID.
• Configuration review: Audit all Apache virtual host and directory configurations to ensure AssignUserID is always set when NiceValue is used.
• Compensating controls: Implement mandatory access controls (e.g., SELinux, AppArmor) to restrict Apache processes even if running as root.
• Monitoring: Deploy file integrity monitoring (FIM) on Apache configuration files and alert on changes to NiceValue directives.
• Least privilege: Run Apache workers under a dedicated, unprivileged system user and avoid using root for any child processes.

Community reactions

The security community has largely treated this as a niche but important vulnerability for shared hosting providers. Discussions on mailing lists and forums emphasize the need for careful configuration management in mpm-itk. The Apache project acknowledged the issue and released a fix in subsequent versions. Some analysts noted that the vulnerability's medium severity understates the risk in multi-tenant environments, where privilege escalation can have cascading impacts. References to this CVE appear in vulnerability databases and security advisories, but it is not widely exploited due to the specific configuration requirement.

Additional resources

• CVE-2011-1176 at NVD
• mpm-itk project page
• Apache HTTP Server security notes
• Wiz vulnerability database entry
• Exploit-DB entry (if available)
• OSS-Security mailing list discussion