CVE-2026-63795
CriticalCVSS 10.0Exploitation Probability (EPSS)
Low risk39th percentile - higher than 39% of all known CVEs
Summary
In the Linux kernel's 9p filesystem, a vulnerability was found in p9_client_walk() due to improper reference counting. When a non-cloning walk fails, the error path incorrectly drops a reference to oldfid, potentially causing a use-after-free or refcount underflow.
Risk Assessment
The risk includes system crashes or local privilege escalation, as an attacker could exploit the memory corruption to compromise kernel integrity.
Recommendation
Apply the latest Linux kernel patch that fixes the reference counting in p9_client_walk(). Check your distribution for the updated package.
Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: 9p: avoid putting oldfid in p9_client_walk() error path When p9_client_walk() is called with clone set to false, fid aliases oldfid. If the walk subsequently fails after the request has been sent, the error path jumps to clunk_fid, which currently calls p9_fid_put(fid) unconditionally. This drops a reference to oldfid even though ownership of oldfid remains with the caller. If this is the last reference, oldfid can be clunked and destroyed while the caller still expects it to be valid. A later use or put of oldfid can then trigger a use-after-free or refcount underflow. Fix this by only putting fid in the clunk_fid error path when it does not alias oldfid, matching the existing guard in the error path below. This can be triggered when a multi-component walk is split into multiple p9_client_walk() calls and a later non-cloning walk fails. A reproducer and refcount warning logs are available on request.