CVE-2025-21655
HighCVSS 7.8Exploitation Probability (EPSS)
Low risk13th percentile - higher than 13% of all known CVEs
Summary
In the Linux kernel's io_uring/eventfd subsystem, a vulnerability was found where io_eventfd_do_signal() called from an RCU callback may directly free the io_ev_fd structure instead of deferring it to another RCU grace period. This could lead to use-after-free or other memory errors.
Risk Assessment
The risk includes potential system instability, kernel panics, or privilege escalation by a local attacker if the vulnerability is exploited.
Recommendation
It is recommended to immediately update the Linux kernel to a version containing the fix (commit addressing this behavior). Monitor official security advisories from your distribution.
Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: io_uring/eventfd: ensure io_eventfd_signal() defers another RCU period io_eventfd_do_signal() is invoked from an RCU callback, but when dropping the reference to the io_ev_fd, it calls io_eventfd_free() directly if the refcount drops to zero. This isn't correct, as any potential freeing of the io_ev_fd should be deferred another RCU grace period. Just call io_eventfd_put() rather than open-code the dec-and-test and free, which will correctly defer it another RCU grace period.