CVE-2021-39634

Local privilege escalation via epoll use-after-free

Published Jan 14, 2022 · Updated Aug 4, 2024

Use-after-free in the Android kernel epoll implementation allows local users to elevate privileges through crafted epoll registrations. The ep_insert path exposes a new epitem to poll wait queues before link insertion and reverse-path checks finish, permitting callbacks to reach freed state. A local app with ordinary execution privileges can trigger the race without user interaction and gain higher permissions on the device.

CVSS severity7.8
High
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

Use-after-free in the Android kernel epoll implementation allows local users to elevate privileges through crafted epoll registrations. The ep_insert path exposes a new epitem to poll wait queues before link insertion and reverse-path checks finish, permitting callbacks to reach freed state. A local app with ordinary execution privileges can trigger the race without user interaction and gain higher permissions on the device.

The record

CVE
CVE-2021-39634
Published
Jan 14, 2022
Updated
Aug 4, 2024
Vendor
Google Cloud
Product
Android
Classifications
CWE-416, T1404
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Jan 14, 2022CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record 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=Android kernel

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

Google Cloud · Androidversion=Android kernel

Published CVSS scores

7.8OSVCVSS: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.

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No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 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
T1404Exploitation 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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