CVE-2021-38497Public exploitNetwork attack vector

Site spoofing via persistent validation popup

Published Nov 3, 2021 · Updated Aug 4, 2024

Origin-validation failure in Firefox before 93, Firefox ESR before 91.2, and Thunderbird before 91.2 allows remote attackers to spoof sites. The XUL Widgets form-validation popup stays visible after window.open() navigates or switches the tab, so attacker-controlled text appears over the destination origin. A user must load and interact with a crafted page; the result is visual deception, with no reported direct data access or code execution.

CVSS severity6.5
Medium
EPSS probability0.55%
Next 30 days · Sep 17, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Origin-validation failure in Firefox before 93, Firefox ESR before 91.2, and Thunderbird before 91.2 allows remote attackers to spoof sites. The XUL Widgets form-validation popup stays visible after window.open() navigates or switches the tab, so attacker-controlled text appears over the destination origin. A user must load and interact with a crafted page; the result is visual deception, with no reported direct data access or code execution.

The record

CVE
CVE-2021-38497
Published
Nov 3, 2021
Updated
Aug 4, 2024
Vendor
Mozilla
Product
Firefox
Classifications
CWE-346
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Nov 3, 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

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 <93

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Mozilla · Firefoxversion=unspecified <93
Mozilla · Thunderbirdversion=unspecified <91.2
Mozilla · Firefox ESRversion=unspecified <91.2

Published CVSS scores

4.3NIST NVDAV:N/AC:M/Au:N/C:N/I:P/A:N
6.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/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 11, 2026Sep 17, 2026
Latest reporting daySep 17, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-346Origin Validation Error

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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