CVE-2013-2178 in Fail2ban
Summary
by MITRE
The apache-auth.conf, apache-nohome.conf, apache-noscript.conf, and apache-overflows.conf files in Fail2ban before 0.8.10 do not properly validate log messages, which allows remote attackers to block arbitrary IP addresses via certain messages in a request.
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Analysis
by VulDB Data Team • 01/07/2022
The vulnerability identified as CVE-2013-2178 represents a critical security flaw in the Fail2ban intrusion prevention software ecosystem, specifically affecting versions prior to 08.10. This issue stems from inadequate input validation within the apache configuration files that govern how Fail2ban processes and interprets log messages from Apache web servers. The affected configuration files including apache-authconf, apache-nohomeconf, apache-noscriptconf, and apache-overflowsconf fail to properly sanitize or validate the content of log entries they process, creating a pathway for malicious actors to exploit the system's automatic blocking mechanisms.
The technical flaw manifests in the improper handling of log message parsing where Fail2ban's configuration files do not adequately filter or validate the data they receive from Apache log files. When these configuration files encounter specially crafted log messages containing malicious payloads, they fail to distinguish between legitimate log entries and crafted attack vectors. This vulnerability operates at the input validation layer, where the system assumes all incoming log data is trustworthy without sufficient sanitization checks. The flaw directly maps to CWE-20, which describes improper input validation, and represents a classic example of how insufficient data sanitization can lead to privilege escalation and unauthorized access control manipulation.
The operational impact of this vulnerability extends beyond simple denial of service scenarios, as it allows remote attackers to manipulate the security controls of systems protected by Fail2ban. An attacker can craft specific HTTP requests or log entries that, when processed by the vulnerable Fail2ban configuration files, will result in arbitrary IP addresses being automatically blocked by the system. This creates a situation where legitimate users or systems can be inadvertently or maliciously excluded from network access, effectively enabling a form of distributed denial of service attack against specific targets. The vulnerability can be exploited from remote locations without requiring authentication, making it particularly dangerous as it can be leveraged by anyone who can send requests to the affected Apache server.
The attack vector for this vulnerability aligns with ATT&CK technique T1562.006, which involves the manipulation of the system's security controls through the exploitation of configuration weaknesses. This particular flaw enables attackers to perform unauthorized access control manipulation by exploiting the trust placed in log message parsing mechanisms. Organizations using vulnerable versions of Fail2ban face significant operational risks as their automated security systems become weaponized against them, potentially blocking legitimate users, systems, or even entire network segments. The vulnerability essentially transforms the security tool from a protective mechanism into an attack vector, undermining the fundamental security posture of systems that depend on Fail2ban for access control enforcement.
Mitigation strategies for this vulnerability require immediate patching of Fail2ban installations to version 0.8.10 or later, where the input validation issues have been addressed. System administrators should also implement additional monitoring and logging controls to detect anomalous patterns in IP blocking activities that might indicate exploitation attempts. Network segmentation and the implementation of additional access control layers can provide defense-in-depth measures while patches are deployed. Security teams should also review and validate the integrity of their Fail2ban configuration files to ensure no malicious modifications have occurred. Regular security assessments of intrusion prevention systems and their configuration files should be conducted to identify similar validation weaknesses in other security tools that process log data from network services.