CVE-2019-3901 in Linux
Summary
by MITRE
A race condition in perf_event_open() allows local attackers to leak sensitive data from setuid programs. As no relevant locks (in particular the cred_guard_mutex) are held during the ptrace_may_access() call, it is possible for the specified target task to perform an execve() syscall with setuid execution before perf_event_alloc() actually attaches to it, allowing an attacker to bypass the ptrace_may_access() check and the perf_event_exit_task(current) call that is performed in install_exec_creds() during privileged execve() calls. This issue affects kernel versions before 4.8.
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Analysis
by VulDB Data Team • 09/06/2023
The vulnerability described in CVE-2019-3901 represents a critical race condition within the Linux kernel's performance monitoring subsystem, specifically affecting the perf_event_open() system call implementation. This flaw exists in kernel versions prior to 4.8 and creates a security loophole that allows local attackers to exploit a timing window during process execution and monitoring attachment. The vulnerability stems from insufficient synchronization mechanisms during the critical path of performance event setup, where concurrent execution paths can lead to unauthorized data access.
The technical root cause of this vulnerability lies in the improper handling of synchronization primitives within the kernel's performance monitoring code. During the perf_event_open() call sequence, the system fails to acquire necessary locks such as cred_guard_mutex before invoking ptrace_may_access() function. This creates a window where a target process can execute an execve() system call with setuid privileges while the performance monitoring subsystem is in the process of attaching to it. The race condition occurs between the point where ptrace_may_access() validates access permissions and where perf_event_alloc() actually establishes the monitoring attachment, allowing malicious processes to bypass security checks that should prevent unauthorized access to privileged processes.
The operational impact of this vulnerability is significant as it enables local attackers to extract sensitive information from setuid programs that would normally be protected from unauthorized access. When a process with elevated privileges executes an execve() call, the kernel's install_exec_creds() function typically performs cleanup operations including perf_event_exit_task(current) calls that should terminate monitoring of the previous process context. However, due to the race condition, an attacker can manipulate timing to ensure that the monitoring attachment occurs after the privilege escalation has already taken place, thereby gaining access to data that should remain confidential. This vulnerability specifically targets the credential management and process monitoring subsystems, creating a path for information disclosure that can be exploited to extract sensitive data from privileged processes.
The implications of this vulnerability align with several cybersecurity frameworks and threat models, particularly those addressing privilege escalation and information disclosure attacks. From a CWE perspective, this represents a race condition vulnerability (CWE-362) that enables unauthorized access through improper synchronization. The ATT&CK framework categorizes this under privilege escalation techniques where local attackers leverage kernel-level timing issues to bypass security controls. The vulnerability also relates to the broader category of kernel-level information disclosure flaws that can be exploited to extract credentials, process memory contents, or other sensitive data from system processes. Organizations should prioritize patching affected kernel versions to address this issue, as the race condition can be reliably exploited by local users with minimal privileges to gain access to sensitive information from programs running with elevated permissions. The fix implemented in kernel versions 4.8 and later involves proper locking mechanisms to ensure that credential validation and performance monitoring attachment occur in a synchronized manner, preventing the race condition from being exploitable.