CVE-2013-1862 in HTTP Server
Summary
by MITRE
mod_rewrite.c in the mod_rewrite module in the Apache HTTP Server 2.2.x before 2.2.25 writes data to a log file without sanitizing non-printable characters, which might allow remote attackers to execute arbitrary commands via an HTTP request containing an escape sequence for a terminal emulator.
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Analysis
by VulDB Data Team • 06/06/2021
The vulnerability described in CVE-2013-1862 affects the mod_rewrite module in Apache HTTP Server versions 2.2.x prior to 2.2.25, representing a critical security flaw that enables remote command execution through improper input sanitization. This issue stems from the module's failure to properly sanitize non-printable characters when writing data to log files, creating a potential attack vector that could be exploited by malicious actors to execute arbitrary commands on affected systems. The vulnerability specifically manifests when an HTTP request contains escape sequences designed for terminal emulators, which are then written to log files without adequate sanitization. The mod_rewrite module, which provides powerful URL rewriting capabilities, becomes a vector for exploitation due to its logging mechanisms that do not adequately filter or escape special characters. This flaw operates at the intersection of logging security and input validation, where the combination of improper character handling and the potential for terminal escape sequences creates a pathway for command injection attacks. The vulnerability is particularly concerning because it leverages legitimate logging functionality to create an attack surface that could be exploited without requiring authentication or elevated privileges.
The technical exploitation of this vulnerability relies on the specific behavior of how Apache handles log file entries and how terminal emulators interpret escape sequences. When an attacker crafts an HTTP request containing non-printable characters or escape sequences that would normally be used in terminal applications, these sequences are written to the server's log files without proper sanitization. If an administrator or security tool subsequently processes these log files using terminal emulators or other applications that interpret escape sequences, the malicious characters could trigger unintended command execution. The flaw is classified as a command injection vulnerability where the attack occurs through the log file processing rather than direct server interaction, making it particularly stealthy and difficult to detect. The vulnerability demonstrates a classic weakness in input validation and output sanitization, where data flows from user input through server processing to log storage without proper filtering mechanisms. This pattern of vulnerability aligns with CWE-77 and CWE-78 categories, which specifically address command injection flaws that occur when untrusted data is incorporated into command strings without proper sanitization. The attack vector operates through the principle that log files, which are typically considered benign storage locations, can become attack surfaces when they contain unsanitized user input.
The operational impact of CVE-2013-1862 extends beyond immediate command execution capabilities to encompass broader system compromise and data integrity risks. An attacker who successfully exploits this vulnerability could gain unauthorized access to the affected server, potentially leading to full system compromise, data exfiltration, or service disruption. The indirect nature of the attack makes it particularly dangerous because it can remain undetected for extended periods, as the malicious activity occurs through log file manipulation rather than direct server exploitation. Organizations using affected Apache versions face significant risk of unauthorized access, especially those with log file monitoring systems that process logs through terminal emulators or similar applications. The vulnerability affects systems that rely on mod_rewrite for URL manipulation and logging, which represents a substantial portion of web server configurations in production environments. The attack requires minimal privileges and can be executed through standard HTTP requests, making it accessible to attackers with basic network access. This vulnerability also impacts compliance and audit requirements, as log files may contain malicious content that could compromise forensic investigations and security monitoring activities. The risk is compounded by the fact that log file processing is often automated, meaning that any system processing these logs could be exploited without direct user interaction.
Mitigation strategies for CVE-2013-1862 focus on both immediate patching and operational security improvements. The primary recommendation is to upgrade to Apache HTTP Server version 2.2.25 or later, which contains the necessary fixes to properly sanitize log file entries and prevent the inclusion of non-printable characters. Organizations should also implement logging security measures that include filtering of special characters in log entries, particularly when these logs are processed by applications that may interpret escape sequences. The implementation of proper input validation and output sanitization practices should be reinforced throughout the application stack, ensuring that all user-supplied data is properly escaped before being written to any storage mechanisms. Security teams should review their log processing workflows to identify any applications or tools that may interpret terminal escape sequences from log files and implement appropriate safeguards. The vulnerability highlights the importance of the principle of least privilege in log file handling, where access to log files should be restricted to authorized personnel only. Organizations should also implement monitoring solutions that can detect anomalous log file entries or unusual patterns that might indicate exploitation attempts. Additional defensive measures include regular security audits of log handling processes, implementation of web application firewalls that can detect and block malicious input patterns, and ensuring that log file access controls are properly configured. This vulnerability serves as a reminder of the critical importance of input sanitization in all components of web applications, particularly those that handle user data in logging or audit contexts.