CVE-2021-4127Network attack vector

Unspecified impact from outdated ANGLE library

Published Dec 22, 2022 · Updated Apr 16, 2025

Outdated ANGLE graphics code in Mozilla Thunderbird and Firefox ESR before 78.9 allows attackers to cause an unspecified impact. Mozilla disclosed no single defect; the bundled ANGLE revision lagged by about 1,000 commits, and the applicable security-fix subset was unidentified. Exploitation requires graphics content to reach ANGLE, while disabled email scripting limits ordinary-message exposure in Thunderbird.

CVSS severity9.8
Critical
EPSS probability0.90%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Outdated ANGLE graphics code in Mozilla Thunderbird and Firefox ESR before 78.9 allows attackers to cause an unspecified impact. Mozilla disclosed no single defect; the bundled ANGLE revision lagged by about 1,000 commits, and the applicable security-fix subset was unidentified. Exploitation requires graphics content to reach ANGLE, while disabled email scripting limits ordinary-message exposure in Thunderbird.

The record

CVE
CVE-2021-4127
Published
Dec 22, 2022
Updated
Apr 16, 2025
Vendor
Mozilla
Product
Thunderbird
Classifications
Unavailable
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Dec 22, 2022CVE publishedPublication date reported by the CVE source.
  2. Apr 16, 2025Record 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 <78.9

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Mozilla · Thunderbirdversion=unspecified <78.9
Mozilla · Firefox ESRversion=unspecified <78.9

Published CVSS scores

9.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
9.8CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/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 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

No sourced classifications are available.

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

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo