CVE-2021-46958

Local privilege escalation via Btrfs log-root use-after-free

Published Feb 27, 2024 · Updated Aug 5, 2026

Use-after-free in the Btrfs log-sync path in Linux allows local users to escalate privileges or crash the host during fsync. btrfs_sync_log retains a local pointer to fs_info->log_root_tree while an aborted transaction clears and frees that tree, then dereferences the stale pointer during log synchronization. Exploitation requires local file access on a mounted Btrfs volume and a concurrent transaction abort; successful triggering can corrupt kernel memory or interrupt the entire host.

CVSS severity7.8
High
EPSS probability0.24%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Use-after-free in the Btrfs log-sync path in Linux allows local users to escalate privileges or crash the host during fsync. btrfs_sync_log retains a local pointer to fs_info->log_root_tree while an aborted transaction clears and frees that tree, then dereferences the stale pointer during log synchronization. Exploitation requires local file access on a mounted Btrfs volume and a concurrent transaction abort; successful triggering can corrupt kernel memory or interrupt the entire host.

The record

CVE
CVE-2021-46958
Published
Feb 27, 2024
Updated
Aug 5, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
CWE-416, T1499.004, T1068
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Feb 27, 2024CVE publishedPublication date reported by the CVE source.
  2. Aug 5, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

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

  1. Affected versionversion=5.7
  2. Affected versionversion=ef67963dac255b293e19815ea3d440567be4626f <061dde8245356d8864d29e25207aa4daa0be4d3c
  3. Affected versionversion=ef67963dac255b293e19815ea3d440567be4626f <633f7f216663587f17601eaa1cf2ac3d5654874c
  4. Affected versionversion=ef67963dac255b293e19815ea3d440567be4626f <a4794be7b00b7eda4b45fffd283ab7d76df7e5d6
  5. Affected versionversion=ef67963dac255b293e19815ea3d440567be4626f <e2da98788369bfba1138bada72765c47989a4338

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=5.7; version=ef67963dac255b293e19815ea3d440567be4626f <061dde8245356d8864d29e25207aa4daa0be4d3c; version=ef67963dac255b293e19815ea3d440567be4626f <633f7f216663587f17601eaa1cf2ac3d5654874c; version=ef67963dac255b293e19815ea3d440567be4626f <a4794be7b00b7eda4b45fffd283ab7d76df7e5d6; version=ef67963dac255b293e19815ea3d440567be4626f <e2da98788369bfba1138bada72765c47989a4338

Published CVSS scores

7.8Linux kernel CVE teamCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

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

CWE-416Use After Free
T1499.004Application or System Exploitation
T1068Exploitation for Privilege Escalation

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

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo