Linux: Use After Free
CVE-2025-21915 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 d7b339bbc887bcfc1a5b620bfc70c6fbb8f733bf, 8473135f89c0949436a22adb05b8cece2fb3da91, 0439d541aa8d3444ad41c39e39eb71acb57acde3 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 0.23% 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 d7b339bbc887bcfc1a5b620bfc70c6fbb8f733bf or 8473135f89c0949436a22adb05b8cece2fb3da91 or 0439d541aa8d3444ad41c39e39eb71acb57acde3 or 91d44c1afc61a2fec37a9c7a3485368309391e0b, whichever matches your release line, or a later version.
- Update Linux Kernel to 6.6.83 or 6.12.19 or 6.13.7, whichever matches your release line, or a later version.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Linux | Linux | 2959ab247061e67485d83b6af8feb3761ec08cb9 up to, but not including, d7b339bbc887bcfc1a5b620bfc70c6fbb8f733bf; 2959ab247061e67485d83b6af8feb3761ec08cb9 up to, but not including, 8473135f89c0949436a22adb05b8cece2fb3da91; 2959ab247061e67485d83b6af8feb3761ec08cb9 up to, but not including, 0439d541aa8d3444ad41c39e39eb71acb57acde3; 2959ab247061e67485d83b6af8feb3761ec08cb9 up to, but not including, 91d44c1afc61a2fec37a9c7a3485368309391e0b; 6.4 | d7b339bbc887bcfc1a5b620bfc70c6fbb8f733bf, 8473135f89c0949436a22adb05b8cece2fb3da91, 0439d541aa8d3444ad41c39e39eb71acb57acde3, 91d44c1afc61a2fec37a9c7a3485368309391e0b |
| Linux | Linux Kernel | 6.4 up to, but not including, 6.6.83; 6.7 up to, but not including, 6.12.19; 6.13 up to, but not including, 6.13.7; 6.14 | 6.6.83, 6.12.19, 6.13.7 |
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 | 7.0 | High | CNA |
| CVSS 3.1 | 7.8 | High | NVD |
| CVSS 3.1 | 7.8 | High | CISA (ADP) |
Official description
In the Linux kernel, the following vulnerability has been resolved: cdx: Fix possible UAF error in driver_override_show() Fixed a possible UAF problem in driver_override_show() in drivers/cdx/cdx.c This function driver_override_show() is part of DEVICE_ATTR_RW, which includes both driver_override_show() and driver_override_store(). These functions can be executed concurrently in sysfs. The driver_override_store() function uses driver_set_override() to update the driver_override value, and driver_set_override() internally locks the device (device_lock(dev)). If driver_override_show() reads cdx_dev->driver_override without locking, it could potentially access a freed pointer if driver_override_store() frees the string concurrently. This could lead to printing a kernel address, which is a security risk since DEVICE_ATTR can be read by all users. Additionally, a similar pattern is used in drivers/amba/bus.c, as well as many other bus drivers, where device_lock() is taken in the show function, and it has been working without issues. This potential bug was detected by our experimental static analysis tool, which analyzes locking APIs and paired functions to identify data races and atomicity violations.
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
Recent Use After Free vulnerabilities
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