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CVE-2026-89639 (GCVE-0-2026-89639)

Vulnerability from cvelistv5 – Published: 2026-09-11 19:45 – Updated: 2026-09-13 06:32
VLAI
Title
cifs: use cifs_invalidate_cache() in cifs_do_truncate() for O_TRUNC
Summary
In the Linux kernel, the following vulnerability has been resolved: cifs: use cifs_invalidate_cache() in cifs_do_truncate() for O_TRUNC cifs_do_truncate() is invoked from cifs_open() without i_rwsem, so it cannot use cifs_resize_file_locked() to perform a proper fscache cookie resize. Instead, add cifs_invalidate_cache() after cifs_setsize(). cifs_invalidate_cache() calls fscache_invalidate(), which works without holding i_rwsem: it unconditionally increments inval_counter and sets FSCACHE_COOKIE_NO_DATA_TO_READ, ensuring that stale cached data is not served once the cookie is later activated by fscache_use_cookie(). Truncation to zero leaves no valid cached data, making invalidation the correct semantic here.
Severity
7.1 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: efbcecdecefc26fa062c0e8210533ccad7d6bd4a , < 8b9b10fe5b8b492b27b9f4546742ea541a650213 (git)
Affected: fa724e235cfdb0fb0bb427d0f9dfe864ae27403e , < 81fc3868a7f726980ff845c1d0d271051e5f0f45 (git)
Affected: fa724e235cfdb0fb0bb427d0f9dfe864ae27403e , < 364b183230586a62660a7280c1eb20138338eeb5 (git)
Affected: 6838bcac954487cc0a3c8a4ee1b3a3a30e244dc9 (git)
Affected: 75640976cf474eb41682a13f2dbe9534ac26ca50 (git)
Affected: 3513f3931c579ba2a715784c6dedc59e0d9282ee (git)
Affected: 6.18.44 , < 6.18.50 (semver)
Affected: 6.12.105 , < 6.13 (semver)
Affected: 7.1.8 , < 7.2 (semver)
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Linux Linux Affected: 7.2
Unaffected: 0 , < 7.2 (semver)
Unaffected: 6.18.50 , ≤ 6.18.* (semver)
Unaffected: 7.2.4 , ≤ 7.2.* (semver)
Unaffected: 7.3-rc1 , ≤ * (original_commit_for_fix)
guessed Create a notification for this product.
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{
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          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/smb/client/file.c"
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            "version": "3.1"
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              "value": "AV:L - cifs_do_truncate() runs from cifs_open() on the SMB client during a local open/openat with O_TRUNC on a mounted CIFS share (fs/smb/client/), not from ksmbd/nfsd or demux-thread packet parsing; a remote SMB peer cannot invoke this path.\nAC:L - A write-capable open with O_TRUNC deterministically skips fscache invalidation, then the same cifs_open() activates the cookie via fscache_use_cookie(); the attacker can also hold another fd so the cookie is already active, with no race or layout outside their control.\nPR:L - O_TRUNC requires only MAY_WRITE on the target inode, which an ordinary local user has on an already-mounted CIFS share; no init-namespace root, CAP_SYS_ADMIN, or user-namespace mount of CIFS is needed.\nUI:N - The attacker issues open(O_TRUNC) and follow-on reads/writes themselves; on common fstab/autofs/CIFS-home deployments with the fsc option already set, no other user must mount the share or open the file.\nS:U - Stale data stays within the local CIFS client\u0027s fscache and the same SMB file\u0027s contents; this is not a VM escape, IOMMU bypass, or other cross-authority boundary crossing.\nC:H - After O_TRUNC the cookie is activated without FSCACHE_COOKIE_NO_DATA_TO_READ, so later reads (including holes after a size-extending write) can return the full previously truncated file contents that should have been discarded.\nI:H - The same stale cookie presents discarded bytes as current file data and can persist them to the SMB server via netfs read-modify-write/writeback, fully replacing zeros or newly written contents on that file.\nA:N - The flaw is fscache coherency only; it does not oops, panic, deadlock, or exhaust kernel resources, so host availability is unaffected."
            }
          ]
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        "dateUpdated": "2026-09-13T06:32:19.311Z",
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        "shortName": "Linux"
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        },
        {
          "url": "https://git.kernel.org/stable/c/364b183230586a62660a7280c1eb20138338eeb5"
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    "datePublished": "2026-09-11T19:45:32.532Z",
    "dateReserved": "2026-09-11T19:38:34.740Z",
    "dateUpdated": "2026-09-13T06:32:19.311Z",
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    "redhat_vex": {
      "aggregate_severity": "Low",
      "current_release_date": "2026-09-13T07:01:20+00:00",
      "cve": "CVE-2026-89639",
      "id": "CVE-2026-89639",
      "initial_release_date": "2026-09-11T19:45:32.532000+00:00",
      "product_status:known_affected": "2",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: Linux kernel CIFS: Information disclosure due to improper cache invalidation during file truncation",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89639.json",
      "version": "3"
    },
    "suse_vex": {
      "aggregate_severity": "important",
      "current_release_date": "2026-09-13T16:57:42Z",
      "cve": "CVE-2026-89639",
      "id": "CVE-2026-89639",
      "initial_release_date": "2026-09-12T16:24:31Z",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2026-89639",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2026-89639.json",
      "version": "4"
    }
  }
}



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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

Author Source Type Date Other

Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


Detection rules are retrieved from Rulezet.