Linux: Use After Free
CVE-2026-63944 is a high-severity use after free vulnerability in Linux, with a CVSS 3.1 base score of 8.8 out of 10. It can be exploited from the same local network by an unauthenticated attacker, without any action from a user. The record lists versions a55618c0f4cead9e59c63f5ee030d393fd70d861, a921957d39290143629eb38c4f74b9bef8035d0a, d9019210c8c30d40eb20094274cc647e352f48f7 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 0.33% 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 a55618c0f4cead9e59c63f5ee030d393fd70d861 or a921957d39290143629eb38c4f74b9bef8035d0a or d9019210c8c30d40eb20094274cc647e352f48f7 or 380e67b1794a9a281a0cb592b4e62077fbd0c8ca, whichever matches your release line, or a later version.
- Update Linux Kernel to 6.6.143 or 6.12.93 or 6.18.35 or 7.0.12, whichever matches your release line, or a later version.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Linux | Linux | c09b80be6ffc338634b2f5f8cfa12b6843410834 up to, but not including, a55618c0f4cead9e59c63f5ee030d393fd70d861; c09b80be6ffc338634b2f5f8cfa12b6843410834 up to, but not including, a921957d39290143629eb38c4f74b9bef8035d0a; c09b80be6ffc338634b2f5f8cfa12b6843410834 up to, but not including, d9019210c8c30d40eb20094274cc647e352f48f7; c09b80be6ffc338634b2f5f8cfa12b6843410834 up to, but not including, 380e67b1794a9a281a0cb592b4e62077fbd0c8ca; c09b80be6ffc338634b2f5f8cfa12b6843410834 up to, but not including, bfea6091e0fffb270c20e74384b660910277eb6c; 6.4 | a55618c0f4cead9e59c63f5ee030d393fd70d861, a921957d39290143629eb38c4f74b9bef8035d0a, d9019210c8c30d40eb20094274cc647e352f48f7, 380e67b1794a9a281a0cb592b4e62077fbd0c8ca, bfea6091e0fffb270c20e74384b660910277eb6c |
| Linux | Linux Kernel | 6.4 up to, but not including, 6.6.143; 6.7 up to, but not including, 6.12.93; 6.13 up to, but not including, 6.18.35; 6.19 up to, but not including, 7.0.12; 7.1 | 6.6.143, 6.12.93, 6.18.35, 7.0.12 |
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
- AdjacentThe attacker must be on the same local network segment.
- 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
- 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:A/AC:L/PR:N/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: Bluetooth: hci_sync: fix UAF in hci_le_create_cis_sync hci_le_create_cis_sync() dereferences conn->conn_timeout after releasing both rcu_read_lock() and hci_dev_lock(hdev). The conn pointer was obtained from an RCU-protected iteration over hdev->conn_hash.list and is not valid once these locks are dropped. A concurrent disconnect can free the hci_conn between the unlock and the dereference, causing a use-after-free read. The cancellation mechanism in hci_conn_del() cannot prevent this because hci_le_create_cis_pending() queues hci_create_cis_sync with data=NULL: hci_cmd_sync_queue(hdev, hci_create_cis_sync, NULL, NULL); While hci_conn_del() dequeues with data=conn: hci_cmd_sync_dequeue(hdev, NULL, conn, NULL); Since NULL != conn, the lookup in _hci_cmd_sync_lookup_entry() never matches, and the pending work item is not cancelled. Fix this by saving conn->conn_timeout into a local variable while the locks are still held, so the stale conn pointer is never dereferenced after unlock. This is the same class of bug as the one fixed by commit 035c25007c9e ("Bluetooth: hci_sync: Fix UAF on le_read_features_complete") which addressed the identical pattern in a different function. This vulnerability was identified using 0sec.ai, an open-source automated security auditing platform (https://github.com/0sec-labs).
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/380e67b1794a9a281a0cb592b4e62077fbd0c8ca
- git.kernel.org/stable/c/a55618c0f4cead9e59c63f5ee030d393fd70d861
- git.kernel.org/stable/c/a921957d39290143629eb38c4f74b9bef8035d0a
- git.kernel.org/stable/c/bfea6091e0fffb270c20e74384b660910277eb6c
- git.kernel.org/stable/c/d9019210c8c30d40eb20094274cc647e352f48f7
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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