Linux: Use After Free
CVE-2025-39945 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 fde6e73189f40ebcf0633aed2b68e731c25f3aa3, 7b6a5b0a6b392263c3767fc945b311ea04b34bbd, 0405055930264ea8fd26f4131466fa7652e5e47d 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 0.16% 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 fde6e73189f40ebcf0633aed2b68e731c25f3aa3 or 7b6a5b0a6b392263c3767fc945b311ea04b34bbd or 0405055930264ea8fd26f4131466fa7652e5e47d or e1fcd4a9c09feac0902a65615e866dbf22616125, whichever matches your release line, or a later version.
- Update Linux Kernel to 5.4.300 or 5.10.245 or 5.15.194 or 6.1.154, whichever matches your release line, or a later version.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Linux | Linux | fdf24086f4752aee5dfb40143c736250df017820 up to, but not including, fde6e73189f40ebcf0633aed2b68e731c25f3aa3; fdf24086f4752aee5dfb40143c736250df017820 up to, but not including, 7b6a5b0a6b392263c3767fc945b311ea04b34bbd; fdf24086f4752aee5dfb40143c736250df017820 up to, but not including, 0405055930264ea8fd26f4131466fa7652e5e47d; fdf24086f4752aee5dfb40143c736250df017820 up to, but not including, e1fcd4a9c09feac0902a65615e866dbf22616125; fdf24086f4752aee5dfb40143c736250df017820 up to, but not including, 8eeb2091e72d75df8ceaa2172638d61b4cf8929a; fdf24086f4752aee5dfb40143c736250df017820 up to, but not including, 6e33a7eed587062ca8161ad1f4584882a860d697; fdf24086f4752aee5dfb40143c736250df017820 up to, but not including, 0627e1481676669cae2df0d85b5ff13e7d24c390; fdf24086f4752aee5dfb40143c736250df017820 up to, but not including, cfa7d9b1e3a8604afc84e9e51d789c29574fb216; and 1 more ranges | fde6e73189f40ebcf0633aed2b68e731c25f3aa3, 7b6a5b0a6b392263c3767fc945b311ea04b34bbd, 0405055930264ea8fd26f4131466fa7652e5e47d, e1fcd4a9c09feac0902a65615e866dbf22616125, 8eeb2091e72d75df8ceaa2172638d61b4cf8929a, 6e33a7eed587062ca8161ad1f4584882a860d697 |
| Linux | Linux Kernel | 2.6.37 up to, but not including, 5.4.300; 5.5 up to, but not including, 5.10.245; 5.11 up to, but not including, 5.15.194; 5.16 up to, but not including, 6.1.154; 6.2 up to, but not including, 6.6.108; 6.7 up to, but not including, 6.12.49; 6.13 up to, but not including, 6.16.9; 6.17 | 5.4.300, 5.10.245, 5.15.194, 6.1.154, 6.6.108, 6.12.49 |
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.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 7.8 | High | CNA |
| CVSS 3.1 | 7.8 | High | NVD |
Official description
In the Linux kernel, the following vulnerability has been resolved: cnic: Fix use-after-free bugs in cnic_delete_task The original code uses cancel_delayed_work() in cnic_cm_stop_bnx2x_hw(), which does not guarantee that the delayed work item 'delete_task' has fully completed if it was already running. Additionally, the delayed work item is cyclic, the flush_workqueue() in cnic_cm_stop_bnx2x_hw() only blocks and waits for work items that were already queued to the workqueue prior to its invocation. Any work items submitted after flush_workqueue() is called are not included in the set of tasks that the flush operation awaits. This means that after the cyclic work items have finished executing, a delayed work item may still exist in the workqueue. This leads to use-after-free scenarios where the cnic_dev is deallocated by cnic_free_dev(), while delete_task remains active and attempt to dereference cnic_dev in cnic_delete_task(). A typical race condition is illustrated below: CPU 0 (cleanup) | CPU 1 (delayed work callback) cnic_netdev_event() | cnic_stop_hw() | cnic_delete_task() cnic_cm_stop_bnx2x_hw() | ... cancel_delayed_work() | /* the queue_delayed_work() flush_workqueue() | executes after flush_workqueue()*/ | queue_delayed_work() cnic_free_dev(dev)//free | cnic_delete_task() //new instance | dev = cp->dev; //use Replace cancel_delayed_work() with cancel_delayed_work_sync() to ensure that the cyclic delayed work item is properly canceled and that any ongoing execution of the work item completes before the cnic_dev is deallocated. Furthermore, since cancel_delayed_work_sync() uses __flush_work(work, true) to synchronously wait for any currently executing instance of the work item to finish, the flush_workqueue() becomes redundant and should be removed. This bug was identified through static analysis. To reproduce the issue and validate the fix, I simulated the cnic PCI device in QEMU and introduced intentional delays — such as inserting calls to ssleep() within the cnic_delete_task() function — to increase the likelihood of triggering the bug.
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/0405055930264ea8fd26f4131466fa7652e5e47d
- git.kernel.org/stable/c/0627e1481676669cae2df0d85b5ff13e7d24c390
- git.kernel.org/stable/c/6e33a7eed587062ca8161ad1f4584882a860d697
- git.kernel.org/stable/c/7b6a5b0a6b392263c3767fc945b311ea04b34bbd
- git.kernel.org/stable/c/8eeb2091e72d75df8ceaa2172638d61b4cf8929a
- git.kernel.org/stable/c/cfa7d9b1e3a8604afc84e9e51d789c29574fb216
- git.kernel.org/stable/c/e1fcd4a9c09feac0902a65615e866dbf22616125
- git.kernel.org/stable/c/fde6e73189f40ebcf0633aed2b68e731c25f3aa3
Recent Use After Free vulnerabilities
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