Linux: Use After Free
CVE-2026-63802 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 96e545410c4f74c89d496c1d5d9ef8d08f14368b, bbebd9425cad3573d1527441753899b926525a0f, 5e5b7f2ef854936e95dceb6a2fdfefcb7152d2c6 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 0.1% 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 96e545410c4f74c89d496c1d5d9ef8d08f14368b or bbebd9425cad3573d1527441753899b926525a0f or 5e5b7f2ef854936e95dceb6a2fdfefcb7152d2c6 or afebe44facc48a61761e885bbb7f0380d4a603ec, whichever matches your release line, or a later version.
- Update Linux Kernel to 6.4 or 6.6.144 or 6.12.95 or 6.18.38, whichever matches your release line, or a later version.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Linux | Linux | 20cb1c2fb7568a6054c55defe044311397e01ddb up to, but not including, 96e545410c4f74c89d496c1d5d9ef8d08f14368b; 20cb1c2fb7568a6054c55defe044311397e01ddb up to, but not including, bbebd9425cad3573d1527441753899b926525a0f; 20cb1c2fb7568a6054c55defe044311397e01ddb up to, but not including, 5e5b7f2ef854936e95dceb6a2fdfefcb7152d2c6; 20cb1c2fb7568a6054c55defe044311397e01ddb up to, but not including, afebe44facc48a61761e885bbb7f0380d4a603ec; 20cb1c2fb7568a6054c55defe044311397e01ddb up to, but not including, 0ab5ee5a1badb58cbb2242617cb01a4972b1f2a2; 0f6090d90f627d8c58f939067d6c6821ce1b3c68; 6.3.9 up to, but not including, 6.4; 6.4 | 96e545410c4f74c89d496c1d5d9ef8d08f14368b, bbebd9425cad3573d1527441753899b926525a0f, 5e5b7f2ef854936e95dceb6a2fdfefcb7152d2c6, afebe44facc48a61761e885bbb7f0380d4a603ec, 0ab5ee5a1badb58cbb2242617cb01a4972b1f2a2, 6.4 |
| Linux | Linux Kernel | 6.3.9 up to, but not including, 6.4; 6.4.1 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; 6.4 | 6.4, 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 CNA.
Official description
In the Linux kernel, the following vulnerability has been resolved: blk-cgroup: fix UAF in __blkcg_rstat_flush() When multiple blkgs in the same blkcg are released concurrently, a use-after-free can occur. The race happens when one blkg's __blkcg_rstat_flush() removes another blkg's iostat entries via llist_del_all(). The second blkg sees an empty list and proceeds to free itself while the first is still iterating over its entries. Move the flush from __blkg_release() (RCU callback) to blkg_release() (before call_rcu). This ensures the RCU grace period waits for any concurrent flush's rcu_read_lock() section to complete before freeing.
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: total).
- Record last changed materially (score, affected products, status or references).
References
Patches and release notes
- git.kernel.org/stable/c/0ab5ee5a1badb58cbb2242617cb01a4972b1f2a2
- git.kernel.org/stable/c/5e5b7f2ef854936e95dceb6a2fdfefcb7152d2c6
- git.kernel.org/stable/c/96e545410c4f74c89d496c1d5d9ef8d08f14368b
- git.kernel.org/stable/c/afebe44facc48a61761e885bbb7f0380d4a603ec
- git.kernel.org/stable/c/bbebd9425cad3573d1527441753899b926525a0f
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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