CVE-2021-3939Public exploit

Local privilege escalation via static-pointer double free

Published Nov 17, 2021 · Updated Sep 16, 2024

Memory corruption in Canonical AccountsService on Ubuntu 20.04 through 21.10 allows local users to gain root privileges via SetLanguage. In user_change_language_authorized_cb, g_autofree releases fallback_locale even though user_get_fallback_value returns a pointer to static storage, so repeated D-Bus calls double-free it. An unprivileged local account must remove its own .pam_environment file and invoke SetLanguage repeatedly; the root accounts-daemon then crashes or permits administrator-level code execution.

CVSS severity7.8
High
EPSS probability0.37%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Memory corruption in Canonical AccountsService on Ubuntu 20.04 through 21.10 allows local users to gain root privileges via SetLanguage. In user_change_language_authorized_cb, g_autofree releases fallback_locale even though user_get_fallback_value returns a pointer to static storage, so repeated D-Bus calls double-free it. An unprivileged local account must remove its own .pam_environment file and invoke SetLanguage repeatedly; the root accounts-daemon then crashes or permits administrator-level code execution.

The record

CVE
CVE-2021-3939
Published
Nov 17, 2021
Updated
Sep 16, 2024
Vendor
Canonical
Product
AccountsService
Classifications
CWE-763, CWE-590, T1068
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Nov 17, 2021CVE publishedPublication date reported by the CVE source.
  2. Sep 16, 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=0.6.55-0ubuntu12~20.04 <0.6.55-0ubuntu12~20.04.5
  2. Affected versionversion=0.6.55-0ubuntu13 <0.6.55-0ubuntu13.3
  3. Affected versionversion=0.6.55-0ubuntu14 <0.6.55-0ubuntu14.1

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

Canonical · AccountsServiceversion=0.6.55-0ubuntu12~20.04 <0.6.55-0ubuntu12~20.04.5; version=0.6.55-0ubuntu13 <0.6.55-0ubuntu13.3; version=0.6.55-0ubuntu14 <0.6.55-0ubuntu14.1

Published CVSS scores

7.8CanonicalCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
7.2NVDAV:L/AC:L/Au:N/C:C/I:C/A:C
7.8NVDCVSS: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 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 exploitPublished

Weakness, pattern, technique

CWE-763Release of Invalid Pointer or Reference
CWE-590Free of Memory not on the Heap
T1068Exploitation for Privilege Escalation

Public exploit references

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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