CVE-2003-0020 in HTTP Server
Summary
by MITRE
Apache does not filter terminal escape sequences from its error logs, which could make it easier for attackers to insert those sequences into terminal emulators containing vulnerabilities related to escape sequences.
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Analysis
by VulDB Data Team • 05/21/2019
The vulnerability described in CVE-2003-0020 represents a significant security concern within the Apache HTTP Server ecosystem that stems from inadequate input sanitization in error logging mechanisms. This flaw specifically addresses the failure of the Apache web server to properly filter terminal escape sequences when writing error messages to log files, creating potential attack vectors that exploit terminal emulators' handling of such control characters.
The technical nature of this vulnerability resides in the improper handling of escape sequences within Apache's error logging subsystem. When Apache encounters certain error conditions during web server operations, it writes detailed error messages to log files that may contain terminal escape codes such as ANSI escape sequences or other control characters. These sequences are typically used for formatting text in terminal environments but can be exploited when the log files are subsequently viewed or processed by terminal emulators that do not properly sanitize these characters. The vulnerability becomes particularly dangerous when attackers can influence the content of error messages through input manipulation or when log files are displayed in terminal environments that process escape sequences without proper validation.
The operational impact of this vulnerability extends beyond simple logging concerns and creates potential pathways for attackers to exploit terminal emulator vulnerabilities. When security administrators or system operators review Apache error logs, particularly through terminal interfaces or log viewers that interpret escape sequences, they may inadvertently execute malicious commands or trigger display vulnerabilities within their terminal environments. This risk is amplified in environments where multiple users access log files or where automated log analysis tools process these files, as the escape sequences could be interpreted differently by various terminal applications. The vulnerability essentially transforms routine error logging into a potential attack surface that could be leveraged for privilege escalation, information disclosure, or even remote code execution depending on the terminal emulator's response to the malformed escape sequences.
This vulnerability aligns with CWE-116, which addresses the improper encoding or filtering of output, and demonstrates how logging mechanisms can become attack vectors when they fail to properly sanitize data before storage or display. The attack surface is further expanded by ATT&CK technique T1070.004, which covers the manipulation of logs to evade detection, as attackers could potentially use these escape sequences to obscure malicious activity within log files or to manipulate log viewer behavior. Organizations implementing Apache servers without proper mitigation measures face risks that extend from simple information leakage to more severe compromise scenarios, particularly in environments where log files are accessed through terminal interfaces or where automated tools process log data without proper escape sequence filtering.
The recommended mitigations for this vulnerability involve implementing proper input sanitization within Apache's logging mechanisms to strip or encode terminal escape sequences before they are written to log files. System administrators should ensure that Apache configuration includes appropriate logging filters that prevent escape sequences from being stored in error logs. Additionally, organizations should implement proper log file viewing procedures that do not directly process escape sequences, and consider using log management tools that properly sanitize output before display. Regular security audits of logging configurations and input validation mechanisms should be conducted to prevent similar vulnerabilities from emerging in other components of the web server stack. The vulnerability also underscores the importance of considering the entire data flow path from input processing through to output display when implementing security controls, as the issue originates in the logging phase but manifests through terminal display mechanisms.