Description

In ep_free of eventpoll.c, there is a possible use-after-free due to a race condition. This could lead to local escalation of privilege with no additional execution privileges needed. User interaction is not needed for exploitation.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "7.0",
  "pubDate": "2026-10-06T19:18:14.920Z",
  "pubdate": "2026-10-06T19:18:14.920Z",
  "executiveSummary": "A critical use-after-free (UAF) vulnerability has been identified within the ep_free function of the eventpoll.c component in the Linux kernel.\nThe flaw originates from a race condition, allowing for potential local escalation of privilege.\nThis vulnerability is particularly severe because it does not require user interaction, specialized execution privileges, or specific network access, making it exploitable by local, unprivileged users.\nIf successfully exploited, an attacker could achieve arbitrary code execution within the kernel context, leading to complete system compromise.\nThe security implications are significant, as the vulnerability affects the fundamental event notification mechanism (epoll) used by many system services and applications.",
  "technicalDetails": "The vulnerability is rooted in a race condition occurring within the ep_free function of eventpoll.c. The epoll subsystem manages file descriptors for event notification; however, improper synchronization during the teardown process of an eventpoll object leads to a UAF condition.\nThe race condition occurs when concurrent threads attempt to access or release the eventpoll structure while it is being deallocated. If one thread triggers the cleanup process (ep_free) while another thread still maintains a reference or is actively executing operations on the same epoll instance, the kernel may attempt to access memory that has already been freed.\nAn attacker can exploit this by pinning the race condition through carefully timed syscalls, such as epoll_ctl or close, to induce a state where the kernel interacts with a dangling pointer.\nOnce the UAF is triggered, an attacker can manipulate the slab allocator by spraying objects of a similar size to the freed eventpoll memory. By replacing the freed object with attacker-controlled data, the attacker can hijack kernel-level control flow when the kernel subsequently attempts to use the dangling pointer for operations like file descriptor lookup or event delivery.\nThe exploit flow follows these steps: 1. Initiation of multiple threads to stress the epoll teardown path. 2. Inducing the kernel to free the memory associated with the eventpoll object. 3. Immediate reallocation of the freed memory block via user-space heap spraying techniques. 4. Corrupting kernel structures or function pointers residing in the newly allocated buffer. 5. Triggering the use of the corrupted memory by the kernel, resulting in an arbitrary kernel-mode instruction execution or data manipulation.\nBecause this vulnerability resides in the kernel core, successful exploitation bypasses standard user-space protections. The lack of requirement for additional execution privileges means that any local user on a vulnerable system can potentially gain root privileges by redirecting kernel execution to a custom payload (such as a privilege escalation shellcode).\nGiven the nature of the race condition, the window of opportunity is small but exploitable with enough attempts, representing a significant risk to the integrity and availability of the host operating system."
}