CVE-2021-38508Network attack vector

Permission grants via overlaid form validation message

Published Dec 8, 2021 · Updated Aug 4, 2024

UI spoofing in Mozilla Firefox before 94, Firefox ESR before 91.3, and Thunderbird before 91.3 allows remote attackers to obtain permissions. A form-validity message can be positioned over a simultaneous permission prompt, obscuring trusted controls while preserving their click targets. Exploitation requires a crafted page and user interaction; the bounded consequence is a permission grant such as geolocation access.

CVSS severity4.3
Medium
EPSS probability1.53%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

UI spoofing in Mozilla Firefox before 94, Firefox ESR before 91.3, and Thunderbird before 91.3 allows remote attackers to obtain permissions. A form-validity message can be positioned over a simultaneous permission prompt, obscuring trusted controls while preserving their click targets. Exploitation requires a crafted page and user interaction; the bounded consequence is a permission grant such as geolocation access.

The record

CVE
CVE-2021-38508
Published
Dec 8, 2021
Updated
Aug 4, 2024
Vendor
Mozilla
Product
Firefox
Classifications
CWE-1021, CAPEC-103
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Dec 8, 2021CVE 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=unspecified <94

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Mozilla · Firefoxversion=unspecified <94
Mozilla · Thunderbirdversion=unspecified <91.3
Mozilla · Firefox ESRversion=unspecified <91.3

Published CVSS scores

4.3NIST NVDAV:N/AC:M/Au:N/C:N/I:P/A:N
4.3NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/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
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-1021Improper Restriction of Rendered UI Layers or Frames
CAPEC-103Clickjacking

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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