CVE-2021-43531Public exploitNetwork attack vector

Cross-origin URL disclosure via post-redirect context data

Published Dec 8, 2021 · Updated Aug 4, 2024

Same-origin policy bypass in Mozilla Firefox before 94 allows context-dependent attackers to expose redirected image URLs through WebExtensions. The contextMenus.onClicked path copied contextData.srcUrl from mediaURL, returning the final redirect target instead of originalMediaURL to extensions without WebRequest access. A user must open the extension's context menu on a redirected image, after which the extension can read a URL that the same-origin policy otherwise hides.

CVSS severity4.3
Medium
EPSS probability0.33%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Same-origin policy bypass in Mozilla Firefox before 94 allows context-dependent attackers to expose redirected image URLs through WebExtensions. The contextMenus.onClicked path copied contextData.srcUrl from mediaURL, returning the final redirect target instead of originalMediaURL to extensions without WebRequest access. A user must open the extension's context menu on a redirected image, after which the extension can read a URL that the same-origin policy otherwise hides.

The record

CVE
CVE-2021-43531
Published
Dec 8, 2021
Updated
Aug 4, 2024
Vendor
Mozilla
Product
Firefox
Classifications
CWE-346
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

Published CVSS scores

4.3NIST NVDAV:N/AC:M/Au:N/C:P/I:N/A:N
4.3NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/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.

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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 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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