CVE-2025-39779

Local kernel crash via premature writeback-tag clearing

Published Sep 11, 2025 · Updated Sep 11, 2025

A btrfs writeback race in Linux allows local users to crash the kernel during concurrent subpage writes on affected releases. btrfs_subpage_set_writeback clears PAGECACHE_TAG_TOWRITE when only part of a folio enters writeback, so a concurrent WB_SYNC_ALL pass can miss dirty blocks and return before they are flushed. Exploitation requires local access, a subpage folio with a partially dirty range, and concurrent writeback in zoned mode or with compressed writes; the resulting ordering failure can trigger a kernel BUG and stop the system.

CVSS severity5.5
Medium
EPSS probability0.15%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

A btrfs writeback race in Linux allows local users to crash the kernel during concurrent subpage writes on affected releases. btrfs_subpage_set_writeback clears PAGECACHE_TAG_TOWRITE when only part of a folio enters writeback, so a concurrent WB_SYNC_ALL pass can miss dirty blocks and return before they are flushed. Exploitation requires local access, a subpage folio with a partially dirty range, and concurrent writeback in zoned mode or with compressed writes; the resulting ordering failure can trigger a kernel BUG and stop the system.

The record

CVE
CVE-2025-39779
Published
Sep 11, 2025
Updated
Sep 11, 2025
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
T1499
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Sep 11, 2025CVE publishedPublication date reported by the CVE source.
  2. Sep 11, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=3470da3b7d87fde4b9729d4e29c2dc074cd59c10 <3d61136945a7008fc90d013c3c67007ce0c96131
  2. Affected versionversion=3470da3b7d87fde4b9729d4e29c2dc074cd59c10 <b1511360c8ac882b0c52caa263620538e8d73220
  3. Affected versionversion=3470da3b7d87fde4b9729d4e29c2dc074cd59c10 <bce7a5c77a1e7a759e227b7713dde18c52da4759
  4. Affected versionversion=5.13

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=3470da3b7d87fde4b9729d4e29c2dc074cd59c10 <3d61136945a7008fc90d013c3c67007ce0c96131; version=3470da3b7d87fde4b9729d4e29c2dc074cd59c10 <b1511360c8ac882b0c52caa263620538e8d73220; version=3470da3b7d87fde4b9729d4e29c2dc074cd59c10 <bce7a5c77a1e7a759e227b7713dde18c52da4759; version=5.13

Published CVSS scores

5.5NIST NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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