CVE-2026-68442 (GCVE-0-2026-68442)

Vulnerability from cvelistv5 – Published: 2026-08-12 00:07 – Updated: 2026-08-17 05:05
VLAI
Title
btrfs: don't propagate EXTENT_FLAG_LOGGING to split extent maps
Summary
In the Linux kernel, the following vulnerability has been resolved: btrfs: don't propagate EXTENT_FLAG_LOGGING to split extent maps When btrfs_drop_extent_map_range() splits an extent map, the new split maps inherit the original map's flags through a local 'flags' variable. Commit f86f7a75e2fb ("btrfs: use the flags of an extent map to identify the compression type") changed the EXTENT_FLAG_LOGGING clearing to operate on em->flags instead of that local 'flags' copy, so a split of an extent map that is currently being logged wrongly inherits EXTENT_FLAG_LOGGING. The flag is then never cleared on the split, and when it is freed while still on the inode's modified_extents list (for example by the extent map shrinker) it trips the WARN_ON(!list_empty(&em->list)) in btrfs_free_extent_map() and leads to a use-after-free. Clear EXTENT_FLAG_LOGGING from the local 'flags' copy used for the splits and only clear EXTENT_FLAG_PINNED from em->flags, restoring the behaviour prior to f86f7a75e2fb.
Severity
7.8 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: f86f7a75e2fb5fd7d31d00eab8a392f97ba42ce9 , < 2a9246a424f45f33a1b8367052611ebe874868ad (git)
Affected: f86f7a75e2fb5fd7d31d00eab8a392f97ba42ce9 , < 9304713b70e7e1450e3a76e758836fe5391bfa95 (git)
Affected: f86f7a75e2fb5fd7d31d00eab8a392f97ba42ce9 , < 0e465c63f103a5ce6849614d6bda048d70eebec8 (git)
Affected: f86f7a75e2fb5fd7d31d00eab8a392f97ba42ce9 , < 5eff4d5b17fa1950e80bfd1ba43dc0699e61a644 (git)
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Linux Linux Affected: 6.8
Unaffected: 0 , < 6.8 (semver)
Unaffected: 6.12.101 , ≤ 6.12.* (semver)
Unaffected: 6.18.42 , ≤ 6.18.* (semver)
Unaffected: 7.1.6 , ≤ 7.1.* (semver)
Unaffected: 7.2 , ≤ * (original_commit_for_fix)
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/btrfs/extent_map.c"
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          "programFiles": [
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          "vendor": "Linux",
          "versions": [
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              "version": "0",
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              "version": "6.12.101",
              "versionType": "semver"
            },
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              "version": "6.18.42",
              "versionType": "semver"
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              "version": "7.1.6",
              "versionType": "semver"
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                  "versionStartIncluding": "6.8",
                  "vulnerable": true
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                  "versionEndExcluding": "6.18.42",
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          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nbtrfs: don\u0027t propagate EXTENT_FLAG_LOGGING to split extent maps\n\nWhen btrfs_drop_extent_map_range() splits an extent map, the new split\nmaps inherit the original map\u0027s flags through a local \u0027flags\u0027 variable.\nCommit f86f7a75e2fb (\"btrfs: use the flags of an extent map to identify\nthe compression type\") changed the EXTENT_FLAG_LOGGING clearing to\noperate on em-\u003eflags instead of that local \u0027flags\u0027 copy, so a split of\nan extent map that is currently being logged wrongly inherits\nEXTENT_FLAG_LOGGING.\n\nThe flag is then never cleared on the split, and when it is freed while\nstill on the inode\u0027s modified_extents list (for example by the extent\nmap shrinker) it trips the WARN_ON(!list_empty(\u0026em-\u003elist)) in\nbtrfs_free_extent_map() and leads to a use-after-free.\n\nClear EXTENT_FLAG_LOGGING from the local \u0027flags\u0027 copy used for the\nsplits and only clear EXTENT_FLAG_PINNED from em-\u003eflags, restoring the\nbehaviour prior to f86f7a75e2fb."
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            "baseSeverity": "HIGH",
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            "version": "3.1"
          },
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              "lang": "en",
              "value": "AV:L - The bug is in the btrfs in-memory extent map code, reached only through local file operations (write/writeback, fallocate punch hole, truncate, clone, fsync) on a btrfs filesystem; no remote protocol data is involved.\nAC:L - Although the flag is only mis-propagated while an fsync has an extent map flagged for logging, the attacker controls both sides of the race - one thread loops fsync() while another loops writes/punch-hole on the same file - and the resulting bogus map is then freed deterministically by any later drop of that range.\nPR:L - Any unprivileged local user who can create and write a file on a btrfs filesystem (btrfs is the default root fs on several major distros, and /tmp or a home directory suffices) can drive the splitting and logging paths; no capabilities are required.\nUI:N - The attacker performs all the required operations itself (write, punch hole, fsync on its own file); no victim action or administrator involvement is needed.\nS:U - The corruption is confined to kernel memory within the same security authority; there is no crossing of a VM, IOMMU, or other boundary.\nC:H - The freed extent_map stays linked in the inode\u0027s modified_extents list, so later traversal in btrfs_log_changed_extents() dereferences freed slab memory; an attacker who reallocates the object controls what is read back, giving a use-after-free read primitive usable to disclose kernel memory.\nI:H - The dangling list node is written through by list_del_init()/list_add_tail() during fsync, writing attacker-influenced pointers into and from a freed heap object; such list-corruption use-after-frees are the classic basis for arbitrary write and privilege escalation.\nA:H - The bug already trips WARN_ON(!list_empty(\u0026em-\u003elist)) and then operates on freed memory, causing list corruption and an oops or panic (immediately fatal with panic_on_warn or list debugging enabled), which an unprivileged user can trigger repeatedly."
            }
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      "providerMetadata": {
        "dateUpdated": "2026-08-17T05:05:39.676Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
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          "url": "https://git.kernel.org/stable/c/2a9246a424f45f33a1b8367052611ebe874868ad"
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        },
        {
          "url": "https://git.kernel.org/stable/c/5eff4d5b17fa1950e80bfd1ba43dc0699e61a644"
        }
      ],
      "title": "btrfs: don\u0027t propagate EXTENT_FLAG_LOGGING to split extent maps",
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    "assignerShortName": "Linux",
    "cveId": "CVE-2026-68442",
    "datePublished": "2026-08-12T00:07:31.981Z",
    "dateReserved": "2026-07-30T09:28:09.394Z",
    "dateUpdated": "2026-08-17T05:05:39.676Z",
    "state": "PUBLISHED"
  },
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      "date": "2026-08-18",
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      "percentile": "0.0193"
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    "redhat_vex": {
      "aggregate_severity": "Moderate",
      "current_release_date": "2026-08-13T23:27:44+00:00",
      "cve": "CVE-2026-68442",
      "id": "CVE-2026-68442",
      "initial_release_date": "2026-08-12T00:00:00+00:00",
      "product_status:known_affected": "77",
      "product_status:known_not_affected": "199",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: btrfs: don\u0027t propagate EXTENT_FLAG_LOGGING to split extent maps",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-68442.json",
      "version": "3"
    },
    "suse_vex": {
      "aggregate_severity": "moderate",
      "current_release_date": "2026-08-13T01:27:43Z",
      "cve": "CVE-2026-68442",
      "id": "CVE-2026-68442",
      "initial_release_date": "2026-08-12T16:21:53Z",
      "product_status:known_affected": "29",
      "product_status:known_not_affected": "267",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2026-68442",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2026-68442.json",
      "version": "3"
    }
  }
}



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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

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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.