CyberSecBulletin
CVE-2026-64401NVD status: Modified

Linux: Use After Free

Published Updated By the CyberSecBulletin desk

CVE-2026-64401 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 51d18db392e5386a7bb9e816d611f14e600cca3c, aa3c0cab4b28c5007ec570c63e1d6ad6943ed0fd, 945b4a4a54497db1dcb2f20ef801a84e884dac21 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 0.13% 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 51d18db392e5386a7bb9e816d611f14e600cca3c or aa3c0cab4b28c5007ec570c63e1d6ad6943ed0fd or 945b4a4a54497db1dcb2f20ef801a84e884dac21 or 91b8a58c6ac15c7db6518f696389933282f88da7, whichever matches your release line, or a later version.
  2. Update Linux Kernel to 6.1.178 or 6.6.145 or 6.12.97 or 6.18.39, whichever matches your release line, or a later version.

Affected products and versions

VendorProductAffected versionsFixed in
LinuxLinuxfed979a7e082bd9f25f9002c3c4f8740dacd0bc8 up to, but not including, 51d18db392e5386a7bb9e816d611f14e600cca3c; fed979a7e082bd9f25f9002c3c4f8740dacd0bc8 up to, but not including, aa3c0cab4b28c5007ec570c63e1d6ad6943ed0fd; fed979a7e082bd9f25f9002c3c4f8740dacd0bc8 up to, but not including, 945b4a4a54497db1dcb2f20ef801a84e884dac21; fed979a7e082bd9f25f9002c3c4f8740dacd0bc8 up to, but not including, 91b8a58c6ac15c7db6518f696389933282f88da7; fed979a7e082bd9f25f9002c3c4f8740dacd0bc8 up to, but not including, 0700f946659d0ab2352ec8a9b1c6fc74b13a27d7; fed979a7e082bd9f25f9002c3c4f8740dacd0bc8 up to, but not including, ec457f9afe5ae9538bdcd58fd4cb442b9787e183; 5.1151d18db392e5386a7bb9e816d611f14e600cca3c, aa3c0cab4b28c5007ec570c63e1d6ad6943ed0fd, 945b4a4a54497db1dcb2f20ef801a84e884dac21, 91b8a58c6ac15c7db6518f696389933282f88da7, 0700f946659d0ab2352ec8a9b1c6fc74b13a27d7, ec457f9afe5ae9538bdcd58fd4cb442b9787e183
LinuxLinux Kernel5.11 up to, but not including, 6.1.178; 6.2 up to, but not including, 6.6.145; 6.7 up to, but not including, 6.12.97; 6.13 up to, but not including, 6.18.39; 6.19 up to, but not including, 7.1.46.1.178, 6.6.145, 6.12.97, 6.18.39, 7.1.4

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.

Official description

In the Linux kernel, the following vulnerability has been resolved: smb: client: resolve SWN tcon from live registrations cifs_swn_notify() looks up a witness registration by id under cifs_swnreg_idr_mutex, drops the mutex, and then uses the registration's cached tcon pointer. That pointer is not a lifetime reference, and it is not a stable representative once cifs_get_swn_reg() lets multiple tcons for the same net/share name share one registration id. A same-share second mount can keep the cifs_swn_reg alive after the first tcon unregisters and is freed. The registration then still points at the freed first tcon, so taking tc_lock or incrementing tc_count through swnreg->tcon only moves the use-after-free earlier. Taking tc_lock while holding cifs_swnreg_idr_mutex also violates the documented CIFS lock order. Fix this by making the registration store only the stable witness identity: id, net name, share name, and notify flags. When a notify arrives, copy that identity under cifs_swnreg_idr_mutex, drop the mutex, then find and pin a live witness tcon that currently matches the net/share pair under the normal cifs_tcp_ses_lock -> tc_lock order. The notification path uses that pinned tcon directly and drops the reference when done. Registration and unregister messages now use the live tcon passed by the caller instead of a cached tcon in the registration. The final unregister send is folded into cifs_swn_unregister() while the registration is still protected by cifs_swnreg_idr_mutex. This removes the previous find/drop/reacquire raw-pointer window. The release path only removes the idr entry and frees the stable identity strings. This preserves the intended one-registration/many-tcon behavior: a registration id represents a net/share pair, and notify handling acts on a live representative selected at use time. It also preserves CLIENT_MOVE ordering for the representative tcon because the old-IP unregister is sent before cifs_swn_register() sends the new-IP register.

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. CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: total).
  3. Record last changed materially (score, affected products, status or references).

References

Recent Use After Free vulnerabilities

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