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

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.

Timeline

Scores

EPSS (exploitation in 30 days)

0.13% · top 98% of all CVEs (13 Nov 2026)

CISA SSVC

Exploitation: none · Automatable: no · Technical impact: total

The list uses the assigner's score when there is one, then CISA's, then NVD's: High 7.8.

Affected products

• Linux · Linux

  • affected fed979a7e082bd9f25f9002c3c4f8740dacd0bc8 – < 51d18db392e5386a7bb9e816d611f14e600cca3c
  • affected fed979a7e082bd9f25f9002c3c4f8740dacd0bc8 – < aa3c0cab4b28c5007ec570c63e1d6ad6943ed0fd
  • affected fed979a7e082bd9f25f9002c3c4f8740dacd0bc8 – < 945b4a4a54497db1dcb2f20ef801a84e884dac21
  • affected fed979a7e082bd9f25f9002c3c4f8740dacd0bc8 – < 91b8a58c6ac15c7db6518f696389933282f88da7
  • affected fed979a7e082bd9f25f9002c3c4f8740dacd0bc8 – < 0700f946659d0ab2352ec8a9b1c6fc74b13a27d7
  • affected fed979a7e082bd9f25f9002c3c4f8740dacd0bc8 – < ec457f9afe5ae9538bdcd58fd4cb442b9787e183

• Linux · Linux

  • affected 5.11
  • unaffected < 5.11
  • unaffected 6.1.178 – ≤ 6.1.*
  • unaffected 6.6.145 – ≤ 6.6.*
  • unaffected 6.12.97 – ≤ 6.12.*
  • unaffected 6.18.39 – ≤ 6.18.*
  • unaffected 7.1.4 – ≤ 7.1.*
  • unaffected 7.2 – ≤ *

Sources

The same CVE in the primary databases and aggregators, to check against.

• CVE.org record (opens in a new tab)
• CVE List JSON (GitHub) (opens in a new tab)
• NVD (opens in a new tab)
• FIRST EPSS (opens in a new tab)
• EUVD EUVD-2026-48945 (opens in a new tab)
• OSV.dev (opens in a new tab)
• GitHub Advisories (opens in a new tab)
• CIRCL Vulnerability-Lookup (opens in a new tab)

Badge for a README or a ticket

[![CVE-2026-64401](https://cveledger.app/badge/CVE-2026-64401.svg)](https://cveledger.app/cve/CVE-2026-64401)

Record last updated 19 Oct 2026, 20:38 UTC.