CVE-2025-39816

Vulnerability

CVE-2025-39816 is a race condition in the Linux kernel's io_uring subsystem, specifically in the buffer ring (kbuf) implementation. The kernel reads buffer lengths from userspace-mapped memory without using READ_ONCE(), meaning the value can change between reads or be read multiple times inconsistently [1][2]. This can lead to the kernel operating on stale or inconsistent buffer length values.

Exploitation

Exploitation

An attacker with the ability to map and modify the shared buffer ring from userspace can exploit this race. By rapidly changing the buffer length field after the kernel reads it but before it commits the buffer, the attacker can cause the kernel to use an incorrect length. The fix also ensures that if a zero-length buffers stop the incremental commit loop, preventing further progress [1][2].

Impact

Successful exploitation could allow an attacker to corrupt kernel memory, potentially leading to a denial of service (system crash) or, in more severe scenarios, privilege escalation. The CVSS v3 score of 5.5 (Medium) reflects the need for local access and the potential for high impact on integrity and availability.

Mitigation

The vulnerability is fixed in the Linux kernel by commits 390a61d284e1 and 695673eb5711 [1][2]. Users should apply the latest stable kernel updates to mitigate the issue.