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Firefox MobileWeb browser · Mozilla

CVE-2020-26977

MEDIUM · 6.5 CVSS v3.1 Published 2021-01-07
Fix available
A fix is available. Upgrade to 84.0 or later.
See remediation →
72/100
Remediation priority · Elevated
Remotely reachable No privileges

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
By attempting to connect a website using an unresponsive port, an attacker could have controlled the content of a tab while the URL bar displayed the original domain. *Note: This issue only affects Firefox for Android. Other operating systems are unaffected.*. This vulnerability affects Firefox < 84.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

This is a URL spoofing vulnerability in Firefox for Android where an attacker can control tab content while the URL bar displays a legitimate domain. By attempting to connect to a website on an unresponsive port, the browser fails to properly update the URL display, allowing malicious content to appear under the guise of the original domain.

MitigationUpgrade Firefox for Android to version 84 or later to remediate this vulnerability.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Firefox MobileWeb browser
Affected:< 84.0

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
Required
Scope
Unchanged
Confidentiality
None
Integrity
High
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Confirm Firefox for Android is installed
    Check your device settings under Apps or the app drawer for Mozilla Firefox with the Android icon
    Affected if Firefox for Android is present on the device - this vulnerability affects only the Android version, not desktop Firefox
  2. Identify the installed Firefox for Android version
    Open the Google Play Store app, search for Mozilla Firefox, and view the version number under app information, or open Firefox and navigate to Settings > Firefox Accounts to find the version in the About section
    Affected if Version cannot be determined or is below 84.0
  3. Compare your version against the affected range
    Review the version number found in the previous step and compare it to the threshold: versions below 84.0 are affected
    Affected if Your installed version is less than 84.0 (for example, 83.2, 83.1, 82.0, etc.)

If Firefox for Android is installed and the version is below 84.0, the environment is affected by this URL spoofing vulnerability.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

From vendor data
Upgrade available Upgrade to 84.0 or later
Fixed in 84.0
Interim mitigation

Upgrade Firefox for Android to version 84 or later to remediate this vulnerability.

Fix this in Firefox Mobile Scoped from the published advisory
  • Consultation2.0 h
  • Implementation2.0 h
  • Testing1.0 h
  • Review / QA1.0 h
6.0 hours of engineering $1,090
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,744.

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2020-26977 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data