Linux: Double Free
CVE-2026-31609 is a critical-severity double free vulnerability in Linux, with a CVSS 3.1 base score of 9.8 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. The record lists versions a9940dcbe5cb92482c04efc7341039ddf7dbf607, 22b7c1c619d808aec4cad3dc42103345e370d107, f9a162c2bbcd0ac85bd07c5b37cf20286048b65c 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 0.46% chance of exploitation within 30 days, which is low compared with other CVEs.
Critical severity: a successful attack would have severe impact.
What to do
- Update Linux to a9940dcbe5cb92482c04efc7341039ddf7dbf607 or 22b7c1c619d808aec4cad3dc42103345e370d107 or f9a162c2bbcd0ac85bd07c5b37cf20286048b65c or 27b7c3e916218b5eb2ee350211140e961bfc49be, whichever matches your release line, or a later version.
- Update Linux Kernel to 6.18.24 or 6.19.14 or 7.0.1, whichever matches your release line, or a later version.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Linux | Linux | cca0526ef2344cab6944d7f441fc24e152da031b up to, but not including, a9940dcbe5cb92482c04efc7341039ddf7dbf607; 37b5c06956183b65e6808b509cf637632016cdf7 up to, but not including, 22b7c1c619d808aec4cad3dc42103345e370d107; 21538121efe6c8c5b51c742fa02cbe820bc48714 up to, but not including, f9a162c2bbcd0ac85bd07c5b37cf20286048b65c; 21538121efe6c8c5b51c742fa02cbe820bc48714 up to, but not including, 27b7c3e916218b5eb2ee350211140e961bfc49be; 6.18.11 up to, but not including, 6.18.24; 6.19.1 up to, but not including, 6.19.14; 7.0 | a9940dcbe5cb92482c04efc7341039ddf7dbf607, 22b7c1c619d808aec4cad3dc42103345e370d107, f9a162c2bbcd0ac85bd07c5b37cf20286048b65c, 27b7c3e916218b5eb2ee350211140e961bfc49be, 6.18.24, 6.19.14 |
| Linux | Linux Kernel | before 6.18.24; 6.19 up to, but not including, 6.19.14; 7.0 up to, but not including, 7.0.1 | 6.18.24, 6.19.14, 7.0.1 |
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
- NetworkCan be exploited remotely over a network, including the internet.
- 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:N/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: smb: client: avoid double-free in smbd_free_send_io() after smbd_send_batch_flush() smbd_send_batch_flush() already calls smbd_free_send_io(), so we should not call it again after smbd_post_send() moved it to the batch list.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Double Free
The product calls free() twice on the same memory address.
How developers prevent this class of flaw
- Choose a language that provides automatic memory management.
- Ensure that each allocation is freed only once. After freeing a chunk, set the pointer to NULL to ensure the pointer cannot be freed again. In complicated error conditions, be sure that clean-up routines respect the state of allocation properly. If the language is object oriented, ensure that object destructors delete each chunk of memory only once.
- Use a static analysis tool to find double free instances.
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: yes, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Patches and release notes
Recent Double Free vulnerabilities
- 9.8 Critical severity
- 7.8 High severity
- 7.8 High severity
- 7.8 High severity
- 7.8 High severity
- 7.8 High severity
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