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FirefoxWeb browser · Mozilla

CVE-2022-31736

CRITICAL · 9.8 CVSS v3.1 Published 2022-12-22
Fix available
A fix is available. Upgrade to 91.10 / 101 or later.
See remediation →
100/100
Remediation priority · Urgent
Remotely reachable No privileges Zero-click

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
A malicious website could have learned the size of a cross-origin resource that supported Range requests. This vulnerability affects Thunderbird < 91.10, Firefox < 101, and Firefox ESR < 91.10.

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

A malicious website can exploit HTTP Range requests to determine the size of cross-origin resources, enabling attackers to infer sensitive information about resources hosted on other domains through timing or response behavior differences.

MitigationUpdate all affected installations to Firefox 101+, Firefox ESR 91.10+, or Thunderbird 91.10+ to patch the cross-origin information disclosure 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
FirefoxWeb browser
Affected:< 101
Firefox EsrWeb browser
Affected:< 91.10
ThunderbirdApplication
Affected:< 91.10

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
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

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

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. Check Firefox version
    Open Firefox, click the menu button (three horizontal lines), select Help, then About Firefox. The version number is displayed in the window that opens.
    Affected if Version displayed is below 101 (for example, 100.x or lower)
  2. Check Firefox ESR version
    Open Firefox ESR, click the menu button, select Help, then About Firefox ESR. The version number is displayed.
    Affected if Version displayed is below 91.10 (for example, 91.9.x or lower)
  3. Check Thunderbird version
    Open Thunderbird, click the menu button (or Edit menu on Linux), select Help, then About Thunderbird. The version number is displayed.
    Affected if Version displayed is below 91.10 (for example, 91.9.x or lower)
  4. Check via command line (optional)
    On Windows, check registry key HKEY_LOCAL_MACHINE\SOFTWARE\Mozilla\Mozilla Firefox\CurrentVersion or on macOS run: /Applications/Firefox.app/Contents/MacOS/firefox --version
    Affected if Reported version is below 101 or below 91.10 for ESR builds

You are affected if any installed Firefox version is below 101, Firefox ESR is below 91.10, or Thunderbird is below 91.10, since these older versions allow malicious websites to infer cross-origin resource sizes via HTTP Range requests.

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.

dbcve · scoped
Upgrade available Upgrade to 91.10 / 101 or later
Fixed in 91.10101
Interim mitigation

Update all affected installations to Firefox 101+, Firefox ESR 91.10+, or Thunderbird 91.10+ to patch the cross-origin information disclosure vulnerability.

Recommended fix High confidence

Firefox 101, Firefox ESR 91.10, or Thunderbird 91.10 (depending on product)

  1. Close all instances of Firefox, Firefox ESR, or Thunderbird
  2. Back up your profile data as a precaution (profiles are typically in ~/.mozilla/firefox/ or ~/.thunderbird/)
  3. For Firefox: Download and install Firefox 101 or later from www.mozilla.org
  4. For Firefox ESR: Download and install Firefox ESR 91.10 or later from www.mozilla.org
  5. For Thunderbird: Download and install Thunderbird 91.10 or later from www.mozilla.org
  6. Restart the application after installation completes
  7. Verify the installed version by checking Help > About Firefox/Thunderbird
Caveat Standard upgrade - backup profile data before upgrading as a precaution

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Firefox Scoped from the published advisory
  • Consultation2.0 h
  • Implementation1.0 h
  • Testing1.0 h
  • Review / QA1.0 h
5.0 hours of engineering $910
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,456.

Scan for this in your stack

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dbcve dependency scanner

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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-2022-31736 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