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NVD / CVE Program· CNA Linux

CVE-2026-93255: btrfs: make sure EXTENT_BUFFER_READING is cleared under refs_lock

Noroxi assessment

Priority: Monitor (action score 0/100)

  • The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
  • Probability of exploitation in the next 30 days: 0.19% (FIRST EPSS).
  • Fixed version: Linux Linux 2073f3d97b0c5d34fe64812d1237e37bd79c17ec, 690c2accacb1aca91ab8186d15dee56da8723f31, 7.2.

Low priority for now. Upgrade to Linux Linux 2073f3d97b0c5d34fe64812d1237e37bd79c17ec, 690c2accacb1aca91ab8186d15dee56da8723f31, 7.2 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

In the Linux kernel, the following vulnerability has been resolved: btrfs: make sure EXTENT_BUFFER_READING is cleared under refs_lock [FALSE ALERTS] There is a bug report that the warning inside invalidate_and_check_btree_folios() got triggered during btrfs/298: BTRFS info (device sdd): first mount of filesystem f9bf732a-a19b-44b9-99a7-614ddff168e2 BTRFS info (device sdd): using crc32c checksum algorithm BTRFS error (device sdd): failed to find fsid cb2fdb42-b638-4f2f-badd-4127467ba674 when attempting to open seed devices BTRFS error (device sdd): failed to read chunk tree: -2 ------------[ cut here ]------------ WARNING: disk-io.c:3342 at invalidate_and_check_btree_folios+0x260/0x3c0 [btrfs], CPU#4: mount/125993 CPU: 4 UID: 0 PID: 125993 Comm: mount Tainted: G W OE 7.1.0-rc7-custom+ #1 PREEMPT(full) Hardware name: QEMU KVM Virtual Machine, BIOS edk2-20250812-19.fc42 08/12/2025 Call trace: invalidate_and_check_btree_folios+0x260/0x3c0 [btrfs] (P) open_ctree+0x1f50/0x23b0 [btrfs] btrfs_get_tree+0x89c/0xc48 [btrfs] vfs_get_tree+0x30/0x110 vfs_cmd_create+0x58/0xe8 __arm64_sys_fsconfig+0x39c/0x518 invoke_syscall.constprop.0+0x48/0x120 el0_svc_common.constprop.0+0x40/0xe8 do_el0_svc+0x24/0x38 el0_svc+0x50/0x310 el0t_64_sync_handler+0xa0/0xe8 el0t_64_sync+0x198/0x1a0 ---[ end trace 0000000000000000 ]--- BTRFS warning (device sdd): unable to release extent buffer 365985792 owner 3 gen 17 refs 3 flags 0x5 [CAUSE] In that invalidate_and_check_btree_folios() we wait for the eb to finish its read, then check if it's only held by us and the btree inode. If not, then do a warning as it may be still held, and could cause problems. But there is a small window where the check can lead to false alerts: Thread A (Read endio) | Thread B (Unmount) ----------------------------------+------------------------------------- end_bbio_meta_read() | | The eb has one extra ref held | | by the reader, and has | | EXTENT_BUFFER_READING flag set | invalidate_and_check_btree_folios() | | | |- clear_extent_buffer_reading() | | | | |- wait_on_bit_io(); | | | The EXTENT_BUFFER_READING flag is | | | cleared | | |- if (refcount_read(eb->refs) > 2) | | The eb is held by the read, us | | and btree inode, thus it | | will trigger the warning |- free_extent_buffer() | [FIX] Introduce a helper, free_extent_buffer_clear_reading(). If the new parameter, @clear_reading, is set, we will hold the spinlock at the beginning of free_extent_buffer_clear_reading() to make sure the EXTENT_BUFFER_READING flag is cleared inside the same critical section of decreasing refs. Now free_extent_buffer() will just call free_extent_buffer_clear_reading() with @clear_reading set to false, so no behavior change. But for end_bbio_meta_read(), it will not clear_extent_buffer_reading() directly, but pass @clear_reading as true. Then inside invalidate_and_check_btree_folios(), hold the refs_lock before reading refs. So that we eliminate the race window completely.

—No exploit Fix available
Published
Sep 24, 2026
Updated
Oct 19, 2026
EPSS
0.1% · 9th percentile
CWE
—

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Action score

0

Monitor

Low priority for now.

CVSS
0 / 40 · —
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.1%

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Noroxi analysis

What does it mean in your environment?

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Affected systems

Is your version affected?

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Versions reported by the vendor

Affected version ranges reported by the assigning authority (Linux). Independent of NVD's CPE analysis and usually ahead of it.

  • Linux Linux

    • b0c33c0628c5b0678fcae2e05e7b2764149248f8, 7.2affected
    • f5427cab065641a4553d38bb8c4932b8d456c7a7 and later · before 8f7285d608ed0db7c9f09f341547db5ce1351090affected · git
    • 83f7e52b7ed1c3e03b79123e20b6f6adf8d886bb and later · before 2073f3d97b0c5d34fe64812d1237e37bd79c17ecaffected · git
    • 83f7e52b7ed1c3e03b79123e20b6f6adf8d886bb and later · before 690c2accacb1aca91ab8186d15dee56da8723f31affected · git
    • 7.1.8 and later · before 7.2affected · semver
    • before 7.2not affected · semver
    • 7.2.6 and later · up to and including 7.2.*not affected · semver
    • 7.3 and laternot affected · original_commit_for_fix

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
Debian:14linuxbefore 7.2.6-17.2.6-1

Same product

linux: all records

Other highest-scoring records for the same primary product.

  • CVE-2026-74705udp: fix potential use-after-free in tunnel segmentation
    40Plan
  • CVE-2026-74612veth: fix skb length accounting after XDP frag adjustment
    40Plan
  • CVE-2026-74475vxlan: use neigh_ha_snapshot() in route_shortcircuit()
    40Plan

Published before and after this one in the same product

  • ← EarlierCVE-2026-93253Sep 24, 2026 · sched/isolation: Defer freeing of cpumask memblock memory to initcall
    0Monitor
  • ← EarlierCVE-2026-93254Sep 24, 2026 · arm64: entry: Avoid unnecessary local_irq_disable() on kernel exit
    0Monitor
  • Later →CVE-2026-93256Sep 24, 2026 · arm64: hibernate: mask DAIF before restoring hibernated kernel
    0Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
Linux Linux2073f3d97b0c5d34fe64812d1237e37bd79c17ecVendor (CNA)
Linux Linux690c2accacb1aca91ab8186d15dee56da8723f31Vendor (CNA)
Linux Linux7.2Vendor (CNA)
Linux Linux8f7285d608ed0db7c9f09f341547db5ce1351090Vendor (CNA)
debian:linux7.2.6-1 · Debian:14Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

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Timeline

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EPSS, last 120 days

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Patch and commit links

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Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

No CVSS vector for this record, so attack conditions can't be derived.

Weakness class (CWE)

—

Attack context

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Change log

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References

Show all references (2 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

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