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VulnerabilityPublished Updated

CVE-2026-64401: Linux kernel · smb: client: resolve SWN tcon from live registrations

Affects Linux kernelSource CVE Database V5

0

Not known to be exploited · CVSS 7.8 High · fixed in ec457f9afe5ae9538bdcd58fd4cb442b9787e183 : patch Linux kernel soon.

Data as of 26 Oct 2026, 13:47 UTC

CVSS 3.1 base score
7.8High
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.1% chance of exploitation in 30 days – higher than 2% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
CISA SSVC
Exploitation
No evidence of active exploitation and no public proof of concept
Automatable
Attackers cannot reliably automate steps 1–4 of the kill chain
Technical impact
Total control over the software or total information disclosure

CISA SSVC assessment, 2026-10-16.

Patch
Available – fixed in ec457f9afe5ae9538bdcd58fd4cb442b9787e183, aa3c0cab4b28c5007ec570c63e1d6ad6943ed0fd, 945b4a4a54497db1dcb2f20ef801a84e884dac21 +3
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 25 Jul 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponised: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

What to do

Upgrade to a fixed release listed under Affected software.

Affected software

ProductAffectedFixed in
LinuxLinuxAffected
  • ≥ fed979a7e082bd9f25f9002c3c4f8740dacd0bc8, < ec457f9afe5ae9538bdcd58fd4cb442b9787e183
Fixed in
  • ec457f9afe5ae9538bdcd58fd4cb442b9787e183
LinuxLinuxAffected
  • ≥ fed979a7e082bd9f25f9002c3c4f8740dacd0bc8, < aa3c0cab4b28c5007ec570c63e1d6ad6943ed0fd
Fixed in
  • aa3c0cab4b28c5007ec570c63e1d6ad6943ed0fd
LinuxLinuxAffected
  • ≥ fed979a7e082bd9f25f9002c3c4f8740dacd0bc8, < 945b4a4a54497db1dcb2f20ef801a84e884dac21
Fixed in
  • 945b4a4a54497db1dcb2f20ef801a84e884dac21
LinuxLinuxAffected
  • ≥ fed979a7e082bd9f25f9002c3c4f8740dacd0bc8, < 0700f946659d0ab2352ec8a9b1c6fc74b13a27d7
Fixed in
  • 0700f946659d0ab2352ec8a9b1c6fc74b13a27d7
LinuxLinuxAffected
  • ≥ fed979a7e082bd9f25f9002c3c4f8740dacd0bc8, < 91b8a58c6ac15c7db6518f696389933282f88da7
Fixed in
  • 91b8a58c6ac15c7db6518f696389933282f88da7
LinuxLinuxAffected
  • ≥ fed979a7e082bd9f25f9002c3c4f8740dacd0bc8, < 51d18db392e5386a7bb9e816d611f14e600cca3c
Fixed in
  • 51d18db392e5386a7bb9e816d611f14e600cca3c

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.

References

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