CVE-2009-4491 in thttpd
Summary
by MITRE
thttpd 2.25b0 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 • 01/14/2025
The vulnerability identified as CVE-2009-4491 affects thttpd version 2.25b0, a lightweight HTTP server implementation that has been widely deployed in embedded systems and network appliances. This security flaw resides in the server's logging mechanism where it fails to properly sanitize input data before writing to log files, creating a potential vector for terminal escape sequence injection attacks. The issue stems from the server's inadequate handling of non-printable characters that are commonly used in terminal control sequences, particularly those that can manipulate terminal emulators and control window properties.
The technical flaw manifests when thttpd processes HTTP requests containing specially crafted escape sequences that are typically used to control terminal behavior. These sequences, when written to log files without sanitization, can be interpreted by terminal emulators when the logs are viewed or processed. The vulnerability creates a path for remote attackers to potentially manipulate terminal window titles, execute arbitrary commands through terminal emulators that interpret these escape sequences, or even overwrite files if the logging system is improperly configured. This represents a classic case of improper input validation and output encoding, where the server treats user-supplied data as trusted content without proper sanitization.
The operational impact of this vulnerability extends beyond simple log manipulation, as it can potentially enable attackers to compromise the integrity of system logs and gain unauthorized access to system resources. When system administrators or security personnel review log files to investigate security incidents, they may inadvertently execute malicious commands through terminal escape sequences embedded in the logs. This vulnerability particularly affects environments where log files are viewed directly in terminal emulators or processed by applications that interpret escape sequences. The attack vector is particularly concerning in network appliances and embedded systems where thttpd is commonly deployed, as these systems often have limited security controls and may be accessed by untrusted users.
Mitigation strategies for CVE-2009-4491 should focus on implementing proper input sanitization and output encoding mechanisms within the thttpd logging subsystem. Organizations should upgrade to newer versions of thttpd that address this vulnerability, as the original 2.25b0 version lacks proper handling of non-printable characters in log output. Security controls should include filtering or escaping of terminal control sequences before writing data to log files, implementing proper access controls to log files to prevent unauthorized modification, and using centralized logging solutions that properly handle and sanitize log data. Additionally, system administrators should regularly audit log files for suspicious content and implement monitoring solutions that can detect and alert on potentially malicious escape sequences. This vulnerability aligns with CWE-174, which addresses the weakness of insufficient output sanitization, and represents a potential technique for privilege escalation through log manipulation as described in the ATT&CK framework under the T1070.002 sub-technique for "Indicator Removal on Host". Organizations should also consider implementing network segmentation and access controls to limit exposure to this vulnerability while maintaining operational security.