CVE-2021-29951Public exploitNetwork attack vector

Update-service denial via remotely accessible weak DACL

Published Jun 24, 2021 · Updated Aug 3, 2024

Improper privilege management in Firefox before 87 and Firefox ESR or Thunderbird before 78.10.1 allows remote authenticated users to stop updates. The Windows service installer places BUILTIN\Users in the maintenance-service DACL with SERVICE_START and SERVICE_STOP rights. Reachability requires a domain account, remote Service Control Manager access, the maintenance service, and Windows older than Windows 10 build 1709; repeated stop commands interrupt updating.

CVSS severity6.5
Medium
EPSS probability1.85%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper privilege management in Firefox before 87 and Firefox ESR or Thunderbird before 78.10.1 allows remote authenticated users to stop updates. The Windows service installer places BUILTIN\Users in the maintenance-service DACL with SERVICE_START and SERVICE_STOP rights. Reachability requires a domain account, remote Service Control Manager access, the maintenance service, and Windows older than Windows 10 build 1709; repeated stop commands interrupt updating.

The record

CVE
CVE-2021-29951
Published
Jun 24, 2021
Updated
Aug 3, 2024
Vendor
Mozilla
Product
Firefox
Classifications
CWE-269, T1562.001
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Jun 24, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=unspecified <87

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Mozilla · Firefoxversion=unspecified <87
Mozilla · Thunderbirdversion=unspecified <78.10.1
Mozilla · Firefox ESRversion=unspecified <78.10.1

Published CVSS scores

6.5NISTCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
6.4NISTAV:N/AC:L/Au:N/C:P/I:P/A:N

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)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-269Improper Privilege Management
T1562.001Impair Defenses: Disable or Modify Tools

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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