Linux: Use After Free
CVE-2026-31718 is a critical-severity use after 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 0000a7780e0e446a28a273572f6ea8f7f582f694, e33c65f011980b4ad4abfd93585ec2079856368f, 3d6682726c2d3a46d31dae88b8166786b09b03ad 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 0.36% 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 0000a7780e0e446a28a273572f6ea8f7f582f694 or e33c65f011980b4ad4abfd93585ec2079856368f or 3d6682726c2d3a46d31dae88b8166786b09b03ad or b34fc42cfe922e551f7a27d3ac3bb016e41d7dd9, whichever matches your release line, or a later version.
- Update Linux Kernel to 6.7 or 6.12.84 or 6.18.25 or 7.0.2, 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 | 8df4bcdb0a4232192b2445256c39b787d58ef14d up to, but not including, 0000a7780e0e446a28a273572f6ea8f7f582f694; c8efcc786146a951091588e5fa7e3c754850cb3c up to, but not including, e33c65f011980b4ad4abfd93585ec2079856368f; c8efcc786146a951091588e5fa7e3c754850cb3c up to, but not including, 3d6682726c2d3a46d31dae88b8166786b09b03ad; c8efcc786146a951091588e5fa7e3c754850cb3c up to, but not including, b34fc42cfe922e551f7a27d3ac3bb016e41d7dd9; c8efcc786146a951091588e5fa7e3c754850cb3c up to, but not including, 235e32320a470fcd3998fb3774f2290a0eb302a1; 6.6.32 up to, but not including, 6.6.140; 6.9 | 0000a7780e0e446a28a273572f6ea8f7f582f694, e33c65f011980b4ad4abfd93585ec2079856368f, 3d6682726c2d3a46d31dae88b8166786b09b03ad, b34fc42cfe922e551f7a27d3ac3bb016e41d7dd9, 235e32320a470fcd3998fb3774f2290a0eb302a1, 6.6.140 |
| Linux | Linux Kernel | 6.6.32 up to, but not including, 6.7; 6.9 up to, but not including, 6.12.84; 6.13 up to, but not including, 6.18.25; 6.19 up to, but not including, 7.0.2; 7.1 | 6.7, 6.12.84, 6.18.25, 7.0.2 |
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: ksmbd: fix use-after-free in __ksmbd_close_fd() via durable scavenger When a durable file handle survives session disconnect (TCP close without SMB2_LOGOFF), session_fd_check() sets fp->conn = NULL to preserve the handle for later reconnection. However, it did not clean up the byte-range locks on fp->lock_list. Later, when the durable scavenger thread times out and calls __ksmbd_close_fd(NULL, fp), the lock cleanup loop did: spin_lock(&fp->conn->llist_lock); This caused a slab use-after-free because fp->conn was NULL and the original connection object had already been freed by ksmbd_tcp_disconnect(). The root cause is asymmetric cleanup: lock entries (smb_lock->clist) were left dangling on the freed conn->lock_list while fp->conn was nulled out. To fix this issue properly, we need to handle the lifetime of smb_lock->clist across three paths: - Safely skip clist deletion when list is empty and fp->conn is NULL. - Remove the lock from the old connection's lock_list in session_fd_check() - Re-add the lock to the new connection's lock_list in ksmbd_reopen_durable_fd().
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.
- Record last changed materially (score, affected products, status or references).
References
Patches and release notes
Other references
Recent Use After Free vulnerabilities
- 8.1 High severity
- 8.1 High severity
- 7.8 High severity
- 7.0 High severity
- 7.8 High severity
- 7.8 High severity
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