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FirefoxWeb browser · Mozilla

CVE-2022-40956

MEDIUM · 6.1 CVSS v3.1 Published 2022-12-22
Fix available
A fix is available. Upgrade to 102.3 / 105.0 or later.
See remediation →
68/100
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
When injecting an HTML base element, some requests would ignore the CSP's base-uri settings and accept the injected element's base instead. This vulnerability affects Firefox ESR < 102.3, Thunderbird < 102.3, and Firefox < 105.

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 Content Security Policy bypass vulnerability where an injected HTML base element can override the CSP base-uri directive, allowing attackers to control relative URL resolution in affected Firefox and Thunderbird browsers.

MitigationUpdate Firefox to version 105 or later, and Firefox ESR/Thunderbird to version 102.3 or later to patch this CSP bypass 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:< 105.0
Firefox EsrWeb browser
Affected:< 102.3
ThunderbirdApplication
Affected:< 102.3

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
Changed
Confidentiality
Low
Integrity
Low
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/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. Check Firefox version
    In Firefox, go to Help > About Firefox, or navigate to about:support in the address bar, or run: firefox --version
    Affected if The version displayed is below 105.0 (for example, 104.x or earlier)
  2. Check Firefox ESR version
    In Firefox ESR, go to Help > About Firefox, or navigate to about:support in the address bar, or run: firefox --version
    Affected if The version displayed is below 102.3 (for example, 102.2 or earlier)
  3. Check Thunderbird version
    In Thunderbird, go to Help > About Thunderbird, or run: thunderbird --version
    Affected if The version displayed is below 102.3 (for example, 102.2 or earlier)
  4. Confirm browser type
    Verify whether the installed application is standard Firefox, Firefox ESR, or Thunderbird by checking the application name in its About dialog
    Affected if Using Firefox (non-ESR) below 105.0, or Firefox ESR/Thunderbird below 102.3

A user is affected if they are running any version of Firefox below 105.0, Firefox ESR below 102.3, or Thunderbird below 102.3, as these versions contain the CSP base-uri bypass 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.

dbcve · scoped
Upgrade available Upgrade to 102.3 / 105.0 or later
Fixed in 102.3105.0
Interim mitigation

Update Firefox to version 105 or later, and Firefox ESR/Thunderbird to version 102.3 or later to patch this CSP bypass vulnerability.

Recommended fix High confidence

Firefox 105.0 (or Firefox ESR 102.3+ or Thunderbird 102.3+, depending on product)

  1. 1. Back up any critical browser data (bookmarks, saved passwords, extensions) before upgrading
  2. 2. For Firefox: Navigate to Menu > Help > About Firefox to check current version and trigger update to 105.0 or later
  3. 3. For Firefox ESR: Check current version at Menu > Help > About Firefox; if below 102.3, download and install Firefox ESR 102.3 or later from mozilla.org
  4. 4. For Thunderbird: Navigate to Menu > Help > About Thunderbird to check version; if below 102.3, download and install Thunderbird 102.3 or later from mozilla.org
  5. 5. Alternatively, download the appropriate fixed release directly from https://www.mozilla.org/en-US/firefox/releases/ for Firefox or https://www.mozilla.org/en-US/thunderbird/releases/ for Thunderbird
  6. 6. After upgrade, verify the version number matches or exceeds the fixed release (Firefox 105.0+, Firefox ESR 102.3+, Thunderbird 102.3+)
Caveat Standard browser upgrade - verify critical extensions and saved credentials remain functional after updating

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

Fix this in Firefox Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing2.0 h
  • Review / QA1.0 h
9.0 hours of engineering $1,600
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,560.

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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-2022-40956 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