Linux: Use After Free
CVE-2025-21759 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 638e8fe3563a82f298fe537a28d5342a97278cf1, 6901bbb169e3add6c037218d996790cef6b3d650, 7e0a818ecc4d62e7fb668ea02de0bfe8ba0b7dff 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 7.87% chance of exploitation within 30 days, which is in the top 5.21% of all scored CVEs.
High severity with no evidence of exploitation so far.
What to do
- Update Linux to 638e8fe3563a82f298fe537a28d5342a97278cf1 or 6901bbb169e3add6c037218d996790cef6b3d650 or 7e0a818ecc4d62e7fb668ea02de0bfe8ba0b7dff or 81b25a07ebf53f9ef4ca8f3d96a8ddb94561dd5a, whichever matches your release line, or a later version.
- Update Linux Kernel to 6.6.79 or 6.12.16 or 6.13.4, whichever matches your release line, or a later version.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Linux | Linux | b8ad0cbc58f703972e9e37c4e2a8081dd7e6a551 up to, but not including, 638e8fe3563a82f298fe537a28d5342a97278cf1; b8ad0cbc58f703972e9e37c4e2a8081dd7e6a551 up to, but not including, 6901bbb169e3add6c037218d996790cef6b3d650; b8ad0cbc58f703972e9e37c4e2a8081dd7e6a551 up to, but not including, 7e0a818ecc4d62e7fb668ea02de0bfe8ba0b7dff; b8ad0cbc58f703972e9e37c4e2a8081dd7e6a551 up to, but not including, 81b25a07ebf53f9ef4ca8f3d96a8ddb94561dd5a; b8ad0cbc58f703972e9e37c4e2a8081dd7e6a551 up to, but not including, 0bf8e2f3768629d437a32cb824149e6e98254381; b8ad0cbc58f703972e9e37c4e2a8081dd7e6a551 up to, but not including, 8e92d6a413feaf968a33f0b439ecf27404407458; b8ad0cbc58f703972e9e37c4e2a8081dd7e6a551 up to, but not including, 087c1faa594fa07a66933d750c0b2610aa1a2946; 2.6.26 | 638e8fe3563a82f298fe537a28d5342a97278cf1, 6901bbb169e3add6c037218d996790cef6b3d650, 7e0a818ecc4d62e7fb668ea02de0bfe8ba0b7dff, 81b25a07ebf53f9ef4ca8f3d96a8ddb94561dd5a, 0bf8e2f3768629d437a32cb824149e6e98254381, 8e92d6a413feaf968a33f0b439ecf27404407458 |
| Linux | Linux Kernel | 2.6.26 up to, but not including, 6.6.79; 6.7 up to, but not including, 6.12.16; 6.13 up to, but not including, 6.13.4; 6.14 | 6.6.79, 6.12.16, 6.13.4 |
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.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 7.8 | High | CNA |
| CVSS 3.1 | 7.8 | High | CISA (ADP) |
Official description
In the Linux kernel, the following vulnerability has been resolved: ipv6: mcast: extend RCU protection in igmp6_send() igmp6_send() can be called without RTNL or RCU being held. Extend RCU protection so that we can safely fetch the net pointer and avoid a potential UAF. Note that we no longer can use sock_alloc_send_skb() because ipv6.igmp_sk uses GFP_KERNEL allocations which can sleep. Instead use alloc_skb() and charge the net->ipv6.igmp_sk socket under RCU protection.
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
Other references
Recent Use After Free vulnerabilities
- 7.8 High severity
- 7.8 High severity
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- 7.8 High severity
- 9.8 Critical severity
- 7.8 High severity
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