CVE-2020-12391Public exploitNetwork attack vector

Script execution via OBJECT data URL CSP bypass

Published May 26, 2020 · Updated Aug 4, 2024

Content Security Policy bypass in Mozilla Firefox before 76 allows remote attackers to run blocked scripts through crafted web content. When a page creates a data: URL document in an OBJECT element, Firefox fails to copy the embedding context's CSP into the opaque-origin document. Loading attacker-controlled content is sufficient; scripts execute inside a unique opaque origin, limiting access to the embedding page's origin.

CVSS severity7.5
High
EPSS probability1.35%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Content Security Policy bypass in Mozilla Firefox before 76 allows remote attackers to run blocked scripts through crafted web content. When a page creates a data: URL document in an OBJECT element, Firefox fails to copy the embedding context's CSP into the opaque-origin document. Loading attacker-controlled content is sufficient; scripts execute inside a unique opaque origin, limiting access to the embedding page's origin.

The record

CVE
CVE-2020-12391
Published
May 26, 2020
Updated
Aug 4, 2024
Vendor
Mozilla
Product
Firefox
Classifications
CWE-863, T1189
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 26, 2020CVE 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 <76

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Mozilla · Firefoxversion=unspecified <76

Published CVSS scores

5.0NIST NVDAV:N/AC:L/Au:N/C:N/I:P/A:N
7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/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.

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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-863Incorrect Authorization
T1189Drive-by Compromise

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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