CVE-2026-89638smb: client: clear setuid/setgid bit on write with cifsacl/modefromsid/posix extensions

Description

In the Linux kernel, the following vulnerability has been resolved: smb: client: clear setuid/setgid bit on write with cifsacl/modefromsid/posix extensions When a file has the setuid or setgid bit set and is written to, the VFS strips those bits and issues a setattr with ATTR_KILL_SUID/ATTR_KILL_SGID together with an ATTR_MODE carrying the already-cleared mode. Both cifs_setattr_unix() and cifs_setattr_nounix() unconditionally dropped ATTR_MODE in that case: /* skip mode change if it's just for clearing setuid/setgid */ if (attrs->ia_valid & (ATTR_KILL_SUID|ATTR_KILL_SGID)) attrs->ia_valid &= ~ATTR_MODE; This is fine for the default mount, where the mode is only emulated via the DOS read-only attribute and cannot represent the setuid/setgid bits anyway. However, with the "cifsacl" or "modefromsid" mount options the mode is stored on the server through an ACL (id_mode_to_cifs_acl()), with the SMB3.1.1 POSIX extensions the mode is sent to the server directly, and with the SMB1 Unix extensions (cifs_setattr_unix) the mode is sent via CIFSSMBUnixSetPathInfo(). In all those cases dropping ATTR_MODE means the cleared mode is never pushed to the server, so the setuid/setgid bit survives the write. This is a security issue: on local filesystems the setuid bit is stripped when a file is written, but over these cifs.ko mounts the bit persists on the server, potentially allowing an unexpected privilege escalation on subsequent execution. Fix this in two places: 1. cifs_setattr_nounix(): only take the "skip mode change" shortcut when the mode is emulated via the DOS read-only attribute (i.e. neither cifsacl/modefromsid nor the SMB3.1.1 POSIX extensions are in effect), so that the cleared mode is propagated to the server in the ACL / POSIX cases. 2. cifs_setattr_unix(): this function is only called when Unix extensions are in effect, so the mode is always stored on the server. Remove the shortcut entirely so that the cleared mode is always pushed.

Timeline

Scores

EPSS (exploitation in 30 days)

0.18% · top 93% of all CVEs (15 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 d32c4f2626acc385d5187bd5c0c24f442328dc60 – < ce0e675907b887db2b1e44a806118b0a7d8b6b18
  • affected d32c4f2626acc385d5187bd5c0c24f442328dc60 – < a3a0cc83761e46a75b1ed6bfaf35961f2c211148
  • affected d32c4f2626acc385d5187bd5c0c24f442328dc60 – < 2a5206992f526178881e8f5c4644757c336fb76d
  • affected d32c4f2626acc385d5187bd5c0c24f442328dc60 – < 7ceb6f7cb8f8f2b094e0dcdaf75757775d231378
  • affected d32c4f2626acc385d5187bd5c0c24f442328dc60 – < 58b23fc9fb580432470d6c5da3c1e5660dba9fbc
  • affected d32c4f2626acc385d5187bd5c0c24f442328dc60 – < b10015807e4c628095d1d1d1c9307efc8cdd9e1b
  • affected d32c4f2626acc385d5187bd5c0c24f442328dc60 – < 69bfe810ecd1e0387d8975d711cd326341d13c6e
  • affected d32c4f2626acc385d5187bd5c0c24f442328dc60 – < b8e5dc4f95e5484159b343903f302eb6d783f2e6

• Linux · Linux

  • affected 2.6.24
  • unaffected < 2.6.24
  • unaffected 5.10.273 – ≤ 5.10.*
  • unaffected 5.15.224 – ≤ 5.15.*
  • unaffected 6.1.191 – ≤ 6.1.*
  • unaffected 6.6.160 – ≤ 6.6.*
  • unaffected 6.12.113 – ≤ 6.12.*
  • unaffected 6.18.51 – ≤ 6.18.*
  • unaffected 7.2.4 – ≤ 7.2.*
  • unaffected 7.3 – ≤ *

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-2026-76550 (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-2026-89638](https://cveledger.app/badge/CVE-2026-89638.svg)](https://cveledger.app/cve/CVE-2026-89638)

Record last updated 30 Oct 2026, 12:32 UTC.