CVE-2021-47636

Kernel memory disclosure and crash via length misalignment

Published Feb 26, 2025 · Updated Aug 5, 2026

Out-of-bounds read in Linux kernel UBIFS allows local users to disclose kernel memory or crash the system during writeback. ubifs_wbuf_write_nolock aligns a true buffer length upward, then passes the larger aligned byte count to ubifs_leb_write after a partial write, reading beyond the allocated buffer. Reaching the flaw requires write access to an already-mounted UBIFS volume and filesystem operations that fill the journal buffer, create a non-aligned symlink, and trigger inode writeback.

CVSS severity7.1
High
EPSS probability0.25%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Out-of-bounds read in Linux kernel UBIFS allows local users to disclose kernel memory or crash the system during writeback. ubifs_wbuf_write_nolock aligns a true buffer length upward, then passes the larger aligned byte count to ubifs_leb_write after a partial write, reading beyond the allocated buffer. Reaching the flaw requires write access to an already-mounted UBIFS volume and filesystem operations that fill the journal buffer, create a non-aligned symlink, and trigger inode writeback.

The record

CVE
CVE-2021-47636
Published
Feb 26, 2025
Updated
Aug 5, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
CWE-125
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Feb 26, 2025CVE 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

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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=1e51764a3c2ac05a23a22b2a95ddee4d9bffb16d <07a209fadee7b53b46858538e1177597273862e4
  2. Affected versionversion=1e51764a3c2ac05a23a22b2a95ddee4d9bffb16d <3b7fb89135a20587d57f8877c02e25003e9edbdf
  3. Affected versionversion=1e51764a3c2ac05a23a22b2a95ddee4d9bffb16d <4f2262a334641e05f645364d5ade1f565c85f20b
  4. Affected versionversion=1e51764a3c2ac05a23a22b2a95ddee4d9bffb16d <5343575aa11c5d7044107d59d43f84aec01312b0
  5. Affected versionversion=1e51764a3c2ac05a23a22b2a95ddee4d9bffb16d <a7054aaf1909cf40489c0ec1b728fdcf79c751a6
  6. Affected versionversion=1e51764a3c2ac05a23a22b2a95ddee4d9bffb16d <b80ccbec0e4804436c382d7dd60e943c386ed83a
  7. Affected versionversion=1e51764a3c2ac05a23a22b2a95ddee4d9bffb16d <e09fa5318d51f522e1af4fbaf8f74999355980c8
  8. Affected versionversion=2.6.27

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=1e51764a3c2ac05a23a22b2a95ddee4d9bffb16d <07a209fadee7b53b46858538e1177597273862e4; version=1e51764a3c2ac05a23a22b2a95ddee4d9bffb16d <3b7fb89135a20587d57f8877c02e25003e9edbdf; version=1e51764a3c2ac05a23a22b2a95ddee4d9bffb16d <4f2262a334641e05f645364d5ade1f565c85f20b; version=1e51764a3c2ac05a23a22b2a95ddee4d9bffb16d <5343575aa11c5d7044107d59d43f84aec01312b0; version=1e51764a3c2ac05a23a22b2a95ddee4d9bffb16d <a7054aaf1909cf40489c0ec1b728fdcf79c751a6; version=1e51764a3c2ac05a23a22b2a95ddee4d9bffb16d <b80ccbec0e4804436c382d7dd60e943c386ed83a; version=1e51764a3c2ac05a23a22b2a95ddee4d9bffb16d <e09fa5318d51f522e1af4fbaf8f74999355980c8; version=2.6.27

Published CVSS scores

7.1Linux kernel CNACVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H
7.1CISA ADPCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/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

CWE-125Out-of-bounds Read

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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