userfaultfd: fix a race between writeprotect and exit_mmap() (CVE-2021-47461) | HOL Guard CVE

High · CVSS 7.8CVE-2021-47461

userfaultfd: fix a race between writeprotect and exit_mmap()

Answer in brief

CVE-2021-47461 records a High severity (CVSS 7.8) vulnerability in userfaultfd: fix a race between writeprotect and exit_mmap(). The current sources do not mark it as known exploited. The current feed maps Linux/Linux (generic), Linux/Linux (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published May 22, 2024Updated Aug 5, 2026Source checked Sep 19, 2026First seen by HOL Aug 4, 2026Material review Aug 5, 2026

Upstream Advisory

Key facts

Risk: High · CVSS 7.8
Exploitation: Not marked as known exploited
Affected software: 9 mapped packages or products
Fix availability: Available

Why this deserves its current priority

CVSS is 7.8. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps Linux/Linux (generic), Linux/Linux (generic). Check affected ranges and fixed versions before updating.

Affected products and reported versions
Product	Affected versions	Fixed versions
cpe:2.3:o:linux:linux_kernel::::::::	Not reported	Not reported
cpe:2.3:o:linux:linux_kernel:5.15:rc1::::::	Not reported	Not reported
cpe:2.3:o:linux:linux_kernel:5.15:rc2::::::	Not reported	Not reported
cpe:2.3:o:linux:linux_kernel:5.15:rc3::::::	Not reported	Not reported
cpe:2.3:o:linux:linux_kernel:5.15:rc4::::::	Not reported	Not reported
cpe:2.3:o:linux:linux_kernel:5.15:rc5::::::	Not reported	Not reported
cpe:2.3:o:linux:linux_kernel:5.15:rc6::::::	Not reported	Not reported

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
Linux/Linuxgeneric	>=63b2d4174c4ad1f40b48d7138e71bcb564c1fe03 <3cda4bfffd4f755645577aaa9e96a606657b4525 \|\| >=63b2d4174c4ad1f40b48d7138e71bcb564c1fe03 <149958ecd0627a9f1e9c678c25c665400054cd6a \|\| >=63b2d4174c4ad1f40b48d7138e71bcb564c1fe03 <cb185d5f1ebf900f4ae3bf84cee212e6dd035aca	3cda4bfffd4f755645577aaa9e96a606657b4525, 149958ecd0627a9f1e9c678c25c665400054cd6a, cb185d5f1ebf900f4ae3bf84cee212e6dd035aca
Linux/Linuxgeneric	5.7	Not reported

Recommended response

Check inventory. Check lockfiles and deployed manifests for Linux/Linux, Linux/Linux.
Review the reported fix. Update Linux/Linux to 3cda4bfffd4f755645577aaa9e96a606657b4525 if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

Published upstream
May 22, 2024
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Aug 5, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Aug 4, 2026

Sources and claim methodology

Upstream source description

In the Linux kernel, the following vulnerability has been resolved: userfaultfd: fix a race between writeprotect and exit_mmap() A race is possible when a process exits, its VMAs are removed by exit_mmap() and at the same time userfaultfd_writeprotect() is called. The race was detected by KASAN on a development kernel, but it appears to be possible on vanilla kernels as well. Use mmget_not_zero() to prevent the race as done in other userfaultfd operations.

Quoted source text, attributed separately from HOL analysis.