CVE-2021-46933

Kernel memory corruption via repeated eventfd release

Published Feb 27, 2024 · Updated Aug 5, 2026

Use-after-free in Linux kernel FunctionFS 4.0 through 5.15.12 allows local users to crash or corrupt the kernel during gadget teardown. ffs_data_clear releases the same ffs_eventfd reference when ep0 closes and FunctionFS unmounts, underflowing its reference count and leaving a live descriptor tied to freed memory. Reachability requires local control of a FunctionFS instance and an eventfd-bearing descriptor; exploitation permits kernel memory disclosure, modification, or a crash.

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

What happened

Use-after-free in Linux kernel FunctionFS 4.0 through 5.15.12 allows local users to crash or corrupt the kernel during gadget teardown. ffs_data_clear releases the same ffs_eventfd reference when ep0 closes and FunctionFS unmounts, underflowing its reference count and leaving a live descriptor tied to freed memory. Reachability requires local control of a FunctionFS instance and an eventfd-bearing descriptor; exploitation permits kernel memory disclosure, modification, or a crash.

The record

CVE
CVE-2021-46933
Published
Feb 27, 2024
Updated
Aug 5, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
CWE-416, CWE-476, 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

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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=4.0
  2. Affected versionversion=5e33f6fdf735cda1d4580fe6f1878da05718fe73 <1c4ace3e6b8575745c50dca9e76e0021e697d645
  3. Affected versionversion=5e33f6fdf735cda1d4580fe6f1878da05718fe73 <240fc586e83d645912accce081a48aa63a45f6ee
  4. Affected versionversion=5e33f6fdf735cda1d4580fe6f1878da05718fe73 <33f6a0cbb7772146e1c11f38028fffbfed14728b
  5. Affected versionversion=5e33f6fdf735cda1d4580fe6f1878da05718fe73 <52500239e3f2d6fc77b6f58632a9fb98fe74ac09
  6. Affected versionversion=5e33f6fdf735cda1d4580fe6f1878da05718fe73 <b1e0887379422975f237d43d8839b751a6bcf154
  7. Affected versionversion=5e33f6fdf735cda1d4580fe6f1878da05718fe73 <cc8c8028c21b2a3842a1e98e99e55028df275919
  8. Affected versionversion=5e33f6fdf735cda1d4580fe6f1878da05718fe73 <ebef2aa29f370b5096c16020c104e393192ef684
  9. Affected versionversion=5e33f6fdf735cda1d4580fe6f1878da05718fe73 <f976dd7011150244a7ba820f2c331e9fb253befa

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=4.0; version=5e33f6fdf735cda1d4580fe6f1878da05718fe73 <1c4ace3e6b8575745c50dca9e76e0021e697d645; version=5e33f6fdf735cda1d4580fe6f1878da05718fe73 <240fc586e83d645912accce081a48aa63a45f6ee; version=5e33f6fdf735cda1d4580fe6f1878da05718fe73 <33f6a0cbb7772146e1c11f38028fffbfed14728b; version=5e33f6fdf735cda1d4580fe6f1878da05718fe73 <52500239e3f2d6fc77b6f58632a9fb98fe74ac09; version=5e33f6fdf735cda1d4580fe6f1878da05718fe73 <b1e0887379422975f237d43d8839b751a6bcf154; version=5e33f6fdf735cda1d4580fe6f1878da05718fe73 <cc8c8028c21b2a3842a1e98e99e55028df275919; version=5e33f6fdf735cda1d4580fe6f1878da05718fe73 <ebef2aa29f370b5096c16020c104e393192ef684; version=5e33f6fdf735cda1d4580fe6f1878da05718fe73 <f976dd7011150244a7ba820f2c331e9fb253befa

Published CVSS scores

5.5CanonicalCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
7.8Linux kernel CVE teamCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
5.5CISA-ADPCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
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

CWE-416Use After Free
CWE-476NULL Pointer Dereference
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

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Your stack

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