CVE-2015-2831 in das_watchdog
Summary
by MITRE
Buffer overflow in das_watchdog 0.9.0 allows local users to execute arbitrary code with root privileges via a large string in the XAUTHORITY environment variable.
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Analysis
by VulDB Data Team • 11/26/2024
The vulnerability identified as CVE-2015-2831 represents a critical buffer overflow flaw within the das_watchdog utility version 0.9.0, which operates as a watchdog daemon for the Display Access Server. This daemon is responsible for monitoring and managing display server processes, making it a potential target for privilege escalation attacks. The vulnerability specifically manifests when the daemon processes the XAUTHORITY environment variable, which typically contains authentication information for X Window System connections. When a local user provides an excessively long string in this environment variable, the daemon fails to properly validate the input length, leading to memory corruption that can be exploited to execute arbitrary code with elevated privileges.
The technical implementation of this buffer overflow stems from inadequate input validation within the das_watchdog daemon's handling of environment variables. The flaw occurs during the parsing of the XAUTHORITY variable where the daemon allocates a fixed-size buffer without proper bounds checking. This classic buffer overflow vulnerability aligns with CWE-121, which describes heap-based buffer overflow conditions, and CWE-787, which addresses out-of-bounds writes. The vulnerability is particularly dangerous because it allows local privilege escalation from a regular user account to root privileges, as the das_watchdog daemon typically runs with elevated permissions to manage display server processes. Attackers can exploit this by crafting a maliciously long XAUTHORITY string that overflows the allocated buffer and overwrites critical memory segments including return addresses on the stack.
The operational impact of CVE-2015-2831 extends beyond simple privilege escalation, as it provides attackers with complete system control through the watchdog daemon. This vulnerability is particularly concerning in multi-user environments where local users may have access to systems running the affected das_watchdog daemon. The attack vector requires local system access and knowledge of the specific daemon configuration, but once exploited, it provides a persistent backdoor for attackers to maintain elevated privileges. The vulnerability has been classified under the MITRE ATT&CK framework as a privilege escalation technique, specifically falling under the T1068 category for "Exploitation for Privilege Escalation" and T1543 for "Create or Modify System Process." Organizations running display server infrastructure or systems with the affected daemon are at risk of complete system compromise, as the exploitation can lead to persistent access and potential lateral movement within the network.
Mitigation strategies for CVE-2015-2831 must address both immediate remediation and long-term security posture improvements. The primary recommendation is to upgrade to a patched version of the das_watchdog daemon that properly validates input lengths and implements proper bounds checking for environment variables. System administrators should also implement restrictive environment variable handling policies and consider disabling unnecessary watchdog services that may be vulnerable. Additional defensive measures include monitoring for unusual process behavior related to display server management, implementing proper access controls to limit local user privileges, and conducting regular security audits of system services. The vulnerability highlights the importance of secure coding practices and input validation in system-level software, emphasizing that even daemon processes handling privileged operations must implement robust security controls to prevent buffer overflow exploitation. Organizations should also consider implementing runtime protections such as stack canaries and address space layout randomization to make exploitation more difficult even if the underlying vulnerability persists.