CyberSecBulletin
CVE-2026-31703NVD status: Modified

Linux: Use After Free

Published Updated By the CyberSecBulletin desk

CVE-2026-31703 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 382cf81cae89e58d22b4bdc38891cd4d0b9ba921, 19ec404b079be057b387643ba0c69bbcc5867c35, 156cc63691c1f20905510b1007896e090355e6c2 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 0.12% chance of exploitation within 30 days, which is low compared with other CVEs.

Next patch cycle

High severity with no evidence of exploitation so far.

What to do

  1. Update Linux to 382cf81cae89e58d22b4bdc38891cd4d0b9ba921 or 19ec404b079be057b387643ba0c69bbcc5867c35 or 156cc63691c1f20905510b1007896e090355e6c2 or 028103656b84273c73e9e271cf95c9f3421f4b8a, whichever matches your release line, or a later version.
  2. Update Linux Kernel to 6.18.25 or 7.0.2, whichever matches your release line, or a later version.

Affected products and versions

VendorProductAffected versionsFixed in
LinuxLinuxd072b38a64ddbc2d58c2e525a24af24ecbfebcb7 up to, but not including, 382cf81cae89e58d22b4bdc38891cd4d0b9ba921; ac7b2c21f2269d815ad0cdf0f8258d55185b805c up to, but not including, 19ec404b079be057b387643ba0c69bbcc5867c35; fabfc1fcddc5d8185722d4fde5f0968c4760b71e up to, but not including, 156cc63691c1f20905510b1007896e090355e6c2; e1b849cfa6b61f1c866a908c9e8dd9b5aaab820b up to, but not including, 028103656b84273c73e9e271cf95c9f3421f4b8a; e1b849cfa6b61f1c866a908c9e8dd9b5aaab820b up to, but not including, 9223e5f30403a9b506d6d0bff4f2e29a2d7d46af; e1b849cfa6b61f1c866a908c9e8dd9b5aaab820b up to, but not including, 6689f01d6740cf358932b3e97ee968c6099800d9; 6.18382cf81cae89e58d22b4bdc38891cd4d0b9ba921, 19ec404b079be057b387643ba0c69bbcc5867c35, 156cc63691c1f20905510b1007896e090355e6c2, 028103656b84273c73e9e271cf95c9f3421f4b8a, 9223e5f30403a9b506d6d0bff4f2e29a2d7d46af, 6689f01d6740cf358932b3e97ee968c6099800d9
Red HatRed Hat Enterprise Linux 10Not specified in the recordNot stated
Red HatRed Hat Enterprise Linux 6Not specified in the recordNot stated
Red HatRed Hat Enterprise Linux 7Not specified in the recordNot stated
Red HatRed Hat Enterprise Linux 8Not specified in the recordNot stated
Red HatRed Hat Enterprise Linux 9Not specified in the recordNot stated
LinuxLinux Kernel6.18 up to, but not including, 6.18.25; 6.19 up to, but not including, 7.0.2; 7.16.18.25, 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
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 systemScoreSeverityScored by
CVSS 3.17.8HighCNA
CVSS 3.17.0HighCNA

Official description

In the Linux kernel, the following vulnerability has been resolved: writeback: Fix use after free in inode_switch_wbs_work_fn() inode_switch_wbs_work_fn() has a loop like: wb_get(new_wb); while (1) { list = llist_del_all(&new_wb->switch_wbs_ctxs); /* Nothing to do? */ if (!list) break; ... process the items ... } Now adding of items to the list looks like: wb_queue_isw() if (llist_add(&isw->list, &wb->switch_wbs_ctxs)) queue_work(isw_wq, &wb->switch_work); Because inode_switch_wbs_work_fn() loops when processing isw items, it can happen that wb->switch_work is pending while wb->switch_wbs_ctxs is empty. This is a problem because in that case wb can get freed (no isw items -> no wb reference) while the work is still pending causing use-after-free issues. We cannot just fix this by cancelling work when freeing wb because that could still trigger problematic 0 -> 1 transitions on wb refcount due to wb_get() in inode_switch_wbs_work_fn(). It could be all handled with more careful code but that seems unnecessarily complex so let's avoid that until it is proven that the looping actually brings practical benefit. Just remove the loop from inode_switch_wbs_work_fn() instead. That way when wb_queue_isw() queues work, we are guaranteed we have added the first item to wb->switch_wbs_ctxs and nobody is going to remove it (and drop the wb reference it holds) until the queued work runs.

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.

More Use After Free vulnerabilities (CWE-416)

Timeline

  1. CVE record published.
  2. Record last changed materially (score, affected products, status or references).

References

Recent Use After Free vulnerabilities

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