CVE-2026-63795
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.
Does this matter?
High impact if exploited, but EPSS currently rates exploitation as unlikely (0.50%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.
Description
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.
- CVSS 3.1
- 10.0 CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
- EPSS
- 0.50% probability · 42th percentile
- CISA KEV
- Not listed
- Weakness
- CWE-416
- Affected
- linux/linux kernel
- Source
- 416baaa9-dc9f-4396-8d5f-8c081fb06d67
References
- https://git.kernel.org/stable/c/1a3860d46e3eb47dbd60339783cdad7904486b9fPatch
- https://git.kernel.org/stable/c/6dbe9443d9f5f7fb6d319a7b77108853ae6c6beaPatch
- https://git.kernel.org/stable/c/99c379ca1e221c3d75c7c804ebbf4e5ee37a3070Patch
- https://git.kernel.org/stable/c/a61bdcba4f64c2f90d01461913f429ab151f1ca6Patch
- https://git.kernel.org/stable/c/a7656d368265d085ac9bb85ab31b0cdb72ad8c38Patch
- https://git.kernel.org/stable/c/b84f46179c806450b89821221ea5bd9a1698aba8Patch
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.