Linux: Use After Free
CVE-2026-63795 is a critical-severity use after free vulnerability in Linux, with a CVSS 3.1 base score of 10.0 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. The record lists versions 99c379ca1e221c3d75c7c804ebbf4e5ee37a3070, b84f46179c806450b89821221ea5bd9a1698aba8, a61bdcba4f64c2f90d01461913f429ab151f1ca6 as the first without the flaw, so updating Linux to one of those releases or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.61% chance of exploitation within 30 days, higher than 50% of scored CVEs.
Critical severity: a successful attack would have severe impact.
What to do
- Update Linux to 99c379ca1e221c3d75c7c804ebbf4e5ee37a3070 or b84f46179c806450b89821221ea5bd9a1698aba8 or a61bdcba4f64c2f90d01461913f429ab151f1ca6 or 6dbe9443d9f5f7fb6d319a7b77108853ae6c6bea, whichever matches your release line, or a later version.
- Update Linux Kernel to 6.1.177 or 6.6.144 or 6.12.95 or 6.18.38, whichever matches your release line, or a later version.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Linux | Linux | b48dbb998d70b7f48c2ec0a15c3cf47136808e4e up to, but not including, 99c379ca1e221c3d75c7c804ebbf4e5ee37a3070; b48dbb998d70b7f48c2ec0a15c3cf47136808e4e up to, but not including, b84f46179c806450b89821221ea5bd9a1698aba8; b48dbb998d70b7f48c2ec0a15c3cf47136808e4e up to, but not including, a61bdcba4f64c2f90d01461913f429ab151f1ca6; b48dbb998d70b7f48c2ec0a15c3cf47136808e4e up to, but not including, 6dbe9443d9f5f7fb6d319a7b77108853ae6c6bea; b48dbb998d70b7f48c2ec0a15c3cf47136808e4e up to, but not including, a7656d368265d085ac9bb85ab31b0cdb72ad8c38; b48dbb998d70b7f48c2ec0a15c3cf47136808e4e up to, but not including, 1a3860d46e3eb47dbd60339783cdad7904486b9f; 6.0 | 99c379ca1e221c3d75c7c804ebbf4e5ee37a3070, b84f46179c806450b89821221ea5bd9a1698aba8, a61bdcba4f64c2f90d01461913f429ab151f1ca6, 6dbe9443d9f5f7fb6d319a7b77108853ae6c6bea, a7656d368265d085ac9bb85ab31b0cdb72ad8c38, 1a3860d46e3eb47dbd60339783cdad7904486b9f |
| Linux | Linux Kernel | 6.0 up to, but not including, 6.1.177; 6.2 up to, but not including, 6.6.144; 6.7 up to, but not including, 6.12.95; 6.13 up to, but not including, 6.18.38; 6.19 up to, but not including, 7.1.3 | 6.1.177, 6.6.144, 6.12.95, 6.18.38, 7.1.3 |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- Scope
- ChangedThe attack can reach beyond the vulnerable component into other systems.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- HighData or code can be modified at will.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H. Scored by CNA.
Official 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.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Use After Free
The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.
How developers prevent this class of flaw
- Choose a language that provides automatic memory management.
- When freeing pointers, be sure to set them to NULL once they are freed. However, the utilization of multiple or complex data structures may lower the usefulness of this strategy.
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: yes, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Patches and release notes
- git.kernel.org/stable/c/1a3860d46e3eb47dbd60339783cdad7904486b9f
- git.kernel.org/stable/c/6dbe9443d9f5f7fb6d319a7b77108853ae6c6bea
- git.kernel.org/stable/c/99c379ca1e221c3d75c7c804ebbf4e5ee37a3070
- git.kernel.org/stable/c/a61bdcba4f64c2f90d01461913f429ab151f1ca6
- git.kernel.org/stable/c/a7656d368265d085ac9bb85ab31b0cdb72ad8c38
- git.kernel.org/stable/c/b84f46179c806450b89821221ea5bd9a1698aba8
Recent Use After Free vulnerabilities
- 8.8 High severity
- 9.8 Critical severity
- 9.8 Critical severity
- 7.8 High severity
- 9.8 Critical severity
- 8.8 High severity
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