Linux: Use After Free
CVE-2026-63804 is a high-severity use after free vulnerability in Linux, with a CVSS 3.1 base score of 7.8 out of 10. It can be exploited with local access to the system by an attacker with a low-privileged account, without any action from a user. The record lists versions 4fe388218826df8607ae41a6305df67db08a9093, 8745d9f7e1682c39f0a1578895ac74205e2a6757, b85ef03f726b15047a6fa6d11b639bdf6c0ee4f0 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 0.13% chance of exploitation within 30 days, which is low compared with other CVEs.
High severity with no evidence of exploitation so far.
What to do
- Update Linux to 4fe388218826df8607ae41a6305df67db08a9093 or 8745d9f7e1682c39f0a1578895ac74205e2a6757 or b85ef03f726b15047a6fa6d11b639bdf6c0ee4f0 or 9d0d5ba20cad661f7f287d4c66d2c19022ce2fd0, whichever matches your release line, or a later version.
- Update Linux Kernel to 6.6.144 or 6.12.95 or 6.18.38 or 7.1.3, whichever matches your release line, or a later version.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Linux | Linux | a475c5dd16e57c570113eccba51955b5df8bb052 up to, but not including, 4fe388218826df8607ae41a6305df67db08a9093; a475c5dd16e57c570113eccba51955b5df8bb052 up to, but not including, 8745d9f7e1682c39f0a1578895ac74205e2a6757; a475c5dd16e57c570113eccba51955b5df8bb052 up to, but not including, b85ef03f726b15047a6fa6d11b639bdf6c0ee4f0; a475c5dd16e57c570113eccba51955b5df8bb052 up to, but not including, 9d0d5ba20cad661f7f287d4c66d2c19022ce2fd0; a475c5dd16e57c570113eccba51955b5df8bb052 up to, but not including, f9c9ec2c319f843b70ecdf939d48b52d189bc081; 6.6 | 4fe388218826df8607ae41a6305df67db08a9093, 8745d9f7e1682c39f0a1578895ac74205e2a6757, b85ef03f726b15047a6fa6d11b639bdf6c0ee4f0, 9d0d5ba20cad661f7f287d4c66d2c19022ce2fd0, f9c9ec2c319f843b70ecdf939d48b52d189bc081 |
| Linux | Linux Kernel | 6.6 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 | 6.6.144, 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
- LocalThe attacker needs local access or must trick a user into running something.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- LowA basic user account is enough.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- 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:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H. Scored by NVD.
Official description
In the Linux kernel, the following vulnerability has been resolved: gfs2: fix use-after-free in gfs2_qd_dealloc gfs2_qd_dealloc(), called as an RCU callback from gfs2_qd_dispose(), accesses the superblock object sdp through qd->qd_sbd after freeing qd. It does so to decrement sd_quota_count and wake up sd_kill_wait. However, by the time the RCU callback runs, gfs2_put_super() may have already freed sdp via free_sbd(). This can happen when gfs2_quota_cleanup() is called during unmount: it disposes of quota objects via call_rcu() and then waits on sd_kill_wait with a 60-second timeout. If the timeout expires, or if gfs2_gl_hash_clear() triggers additional qd_put() calls that schedule more RCU callbacks after the wait completes, gfs2_put_super() will proceed to free the superblock while RCU callbacks referencing it are still pending. Add an rcu_barrier() before free_sbd() in gfs2_put_super() to ensure all pending RCU callbacks (including gfs2_qd_dealloc) have completed before the superblock is freed.
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: no, technical impact: partial).
- Record last changed materially (score, affected products, status or references).
References
Patches and release notes
- git.kernel.org/stable/c/4fe388218826df8607ae41a6305df67db08a9093
- git.kernel.org/stable/c/8745d9f7e1682c39f0a1578895ac74205e2a6757
- git.kernel.org/stable/c/9d0d5ba20cad661f7f287d4c66d2c19022ce2fd0
- git.kernel.org/stable/c/b85ef03f726b15047a6fa6d11b639bdf6c0ee4f0
- git.kernel.org/stable/c/f9c9ec2c319f843b70ecdf939d48b52d189bc081
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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