CVE-2009-4492 in Ruby
Summary
by MITRE
WEBrick 1.3.1 in Ruby 1.8.6 through patchlevel 383, 1.8.7 through patchlevel 248, 1.8.8dev, 1.9.1 through patchlevel 376, and 1.9.2dev writes data to a log file without sanitizing non-printable characters, which might allow remote attackers to modify a window s title, or possibly execute arbitrary commands or overwrite files, via an HTTP request containing an escape sequence for a terminal emulator.
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Analysis
by VulDB Data Team • 03/24/2025
CVE-2009-4492 represents a significant security vulnerability in WEBrick HTTP server components within Ruby implementations, specifically affecting versions through patchlevel 383 for Ruby 1.8.6, 248 for Ruby 1.8.7, and various versions of Ruby 1.9.x. This vulnerability stems from improper handling of non-printable characters in log file output, creating a potential vector for terminal escape sequence injection attacks that can compromise system integrity and confidentiality.
The technical flaw manifests when WEBrick processes HTTP requests and logs them to files without sanitizing or filtering non-printable characters that may contain terminal escape sequences. These sequences, typically beginning with the escape character ESC (ASCII 27) followed by specific control codes, can instruct terminal emulators to perform various operations including changing window titles, executing commands, or manipulating file systems. The vulnerability occurs because the logging mechanism fails to properly escape or remove these control characters before writing them to log files, creating a scenario where maliciously crafted HTTP requests can embed escape sequences that execute unintended operations when the log files are later viewed or processed.
This vulnerability operates under the broader context of CWE-174, which addresses the weakness of insufficient control of characters in log files, and aligns with ATT&CK technique T1070.002 for "Indicator Removal on Host: File Deletion" and T1070.004 for "Indicator Removal on Host: File and Directory Permissions Modification." The operational impact extends beyond simple log manipulation to potentially enable remote command execution or file system compromise, particularly when log files are processed by terminal emulators or viewed in environments that interpret escape sequences. Attackers can exploit this by crafting HTTP requests containing carefully constructed escape sequences that, when logged, can alter window titles, execute shell commands, or overwrite critical system files depending on the terminal environment and log processing tools used.
The attack vector leverages the fact that many terminal emulators and log viewers interpret escape sequences when displaying log content, creating a chain of execution from HTTP request to system compromise. This vulnerability affects not only the immediate logging functionality but also broader system security through potential privilege escalation scenarios, as log files are often processed with elevated privileges or viewed by system administrators. Organizations should consider this vulnerability in the context of the principle of least privilege and proper input validation, as it demonstrates how seemingly benign logging operations can become attack surfaces when proper sanitization controls are not implemented. Mitigation strategies should include immediate patching of affected Ruby versions, implementation of proper log sanitization mechanisms, and consideration of alternative logging approaches that do not store potentially malicious content in accessible files.