CVE-2025-39698

In the Linux kernel, the following vulnerability has been resolved:

io_uring/futex: ensure io_futex_wait() cleans up properly on failure

The io_futex_data is allocated upfront and assigned to the io_kiocb async_data field, but the request isn't marked with REQ_F_ASYNC_DATA at that point. Those two should always go together, as the flag tells io_uring whether the field is valid or not.

Additionally, on failure cleanup, the futex handler frees the data but does not clear ->async_data. Clear the data and the flag in the error path as well.

Thanks to Trend Micro Zero Day Initiative and particularly ReDress for reporting this.

A flaw in io_uring’s futex path freed io_futex_data on error but left req->async_data and the REQ_F_ASYNC_DATA flag inconsistent, creating a window for use-after-free. This issue is reachable by any unprivileged local user via io_uring futex operations. The most plausible impact is denial of service, since the freed structure is small and not directly attacker-controlled, making exploitation for privilege escalation very unlikely. Still, as with any use-after-free in kernel space, a worst-case impact would be privileges escalation.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

Mitigation for this issue is either not available or the currently available options don't meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability.