CVE-2020-26976Network attack vector

HTTPS iframe interception via missing secure-context check

Published Jan 7, 2021 · Updated Aug 4, 2024

Security-policy bypass in Mozilla Firefox before 84 allows remote attackers to alter HTTPS iframe content via an insecure HTTP parent. The DOM service-worker interception path treated the framed HTTPS client as controllable without first enforcing its secure-context status. Exploitation requires a registered service worker for the HTTPS origin, an HTTPS iframe embedded by an insecure HTTP document, and user interaction with attacker-controlled content.

CVSS severity6.5
Medium
EPSS probability1.62%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Security-policy bypass in Mozilla Firefox before 84 allows remote attackers to alter HTTPS iframe content via an insecure HTTP parent. The DOM service-worker interception path treated the framed HTTPS client as controllable without first enforcing its secure-context status. Exploitation requires a registered service worker for the HTTPS origin, an HTTPS iframe embedded by an insecure HTTP document, and user interaction with attacker-controlled content.

The record

CVE
CVE-2020-26976
Published
Jan 7, 2021
Updated
Aug 4, 2024
Vendor
Mozilla
Product
Firefox
Classifications
Unavailable
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jan 7, 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 <84

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Mozilla · Firefoxversion=unspecified <84

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 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

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

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Your stack

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