CVE-2009-1894 in PulseAudio
Summary
by MITRE
Race condition in PulseAudio 0.9.9, 0.9.10, and 0.9.14 allows local users to gain privileges via vectors involving creation of a hard link, related to the application setting LD_BIND_NOW to 1, and then calling execv on the target of the /proc/self/exe symlink.
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Analysis
by VulDB Data Team • 04/09/2025
The vulnerability described in CVE-2009-1894 represents a sophisticated race condition affecting PulseAudio versions 0.9.9, 0.9.10, and 0.9.14, which enables local privilege escalation through carefully orchestrated file system manipulation. This flaw operates by exploiting the timing window between when a hard link is created and when the system executes a program, specifically targeting the interaction between the LD_BIND_NOW environment variable and the /proc/self/exe symlink mechanism. The vulnerability falls under the category of race conditions as classified by CWE-362, which describes a condition where concurrent operations can lead to unpredictable behavior and security implications.
The technical implementation of this vulnerability involves a precise sequence of system calls and file operations that must occur within a narrow temporal window. An attacker creates a hard link to a target file while PulseAudio is in the process of executing a program, leveraging the fact that LD_BIND_NOW is set to 1, which forces immediate symbol resolution during program loading. This setting, when combined with the /proc/self/exe symlink, creates an opportunity for malicious code execution. The race condition occurs because the system does not properly validate the integrity of the target file between the time when the hard link is created and when execv is called on the symlink target, allowing an attacker to substitute a malicious binary for the legitimate one.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it provides attackers with a mechanism to execute arbitrary code with elevated privileges on systems running affected PulseAudio versions. This type of vulnerability is particularly dangerous in multi-user environments where local users might not have direct access to system resources but can exploit such flaws to gain unauthorized access to system functions. The vulnerability aligns with ATT&CK technique T1068, which covers the exploitation of legitimate credentials and system privileges, and specifically addresses the privilege escalation category within the attack framework.
Mitigation strategies for this vulnerability require immediate patching of affected PulseAudio installations to versions that address the race condition in the application's handling of hard links and execv calls. System administrators should also implement monitoring for unusual hard link creation patterns and ensure that LD_BIND_NOW is not unnecessarily set in contexts where race conditions could occur. Additional protective measures include restricting write permissions on critical system directories and implementing proper file system integrity monitoring to detect unauthorized modifications. The vulnerability demonstrates the importance of proper synchronization mechanisms in system applications and highlights the need for careful consideration of environment variable settings that could interact with file system operations in unexpected ways. Organizations should also consider implementing privilege separation techniques and ensuring that applications do not set environment variables like LD_BIND_NOW unless absolutely necessary for their operation.