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FirefoxWeb browser · Mozilla

CVE-2026-2775

CRITICAL · 9.8 CVSS v3.1 Published 2026-02-24
Fix available
A fix is available. Upgrade to 115.33.0 / 140.8.0 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
Mitigation bypass in the DOM: HTML Parser component. This vulnerability was fixed in Firefox 148, Firefox ESR 115.33, Firefox ESR 140.8, Thunderbird 148, and Thunderbird 140.8.

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 · moderate confidence

This is a mitigation bypass vulnerability in the DOM: HTML Parser component of Firefox and Thunderbird. The vulnerability allows attackers to circumvent existing security controls in the HTML parsing layer, likely enabling injection or execution attacks that would normally be blocked. With a CVSS of 9.8, it is trivially exploitable and can lead to remote code execution.

MitigationApply the vendor-supplied updates by upgrading Firefox to version 148 (or ESR 115.33/140.8) and Thunderbird to version 148 (or 140.8) as specified in the advisory.

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:< 115.33.0< 148.0>= 128.0, < 140.8.0
ThunderbirdApplication
Affected:< 140.8.0< 148.0

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
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 installed Firefox version
    Open Firefox, navigate to Menu > Help > About Firefox, or enter 'about:Firefox' in the address bar to display the version number
    Affected if Version is less than 115.33.0, OR between 128.0 and 140.8.0 exclusive, OR less than 148.0 (if on a rapid release channel)
  2. Check installed Thunderbird version
    Open Thunderbird, navigate to Menu > Help > About Thunderbird to display the version number
    Affected if Version is less than 140.8.0 or less than 148.0 (depending on release channel)
  3. Determine Firefox release channel
    Enter 'about:support' in Firefox address bar and locate the 'Release Channel' entry under Application Basics
    Affected if Release channel is 'release' and version < 148.0, or 'esr' with version < 115.33.0 or < 140.8.0 depending on ESR branch
  4. Verify HTML parser exposure
    The DOM:HTML Parser component is used whenever Firefox or Thunderbird processes HTML content. No additional config check needed - if the application renders web content or HTML emails, the component is active
    Affected if Firefox or Thunderbird is used to browse websites or view HTML email content (default behavior)

A user is affected if their installed Firefox or Thunderbird version falls within the vulnerable ranges and they process HTML content through the browser or email client.

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 115.33.0 / 140.8.0 / 148.0 or later
Fixed in 115.33.0140.8.0148.0
Interim mitigation

Apply the vendor-supplied updates by upgrading Firefox to version 148 (or ESR 115.33/140.8) and Thunderbird to version 148 (or 140.8) as specified in the advisory.

Recommended fix High confidence

Firefox 148 / Firefox ESR 115.33 / Firefox ESR 140.8 / Thunderbird 148 / Thunderbird 140.8

  1. Identify the currently installed Firefox or Thunderbird version via Help > About
  2. For Firefox: If using standard release, upgrade to Firefox 148 or later
  3. For Firefox ESR: If using ESR 115.x, upgrade to Firefox ESR 115.33 or later; if using ESR 128.x or 140.x, upgrade to Firefox ESR 140.8 or later
  4. For Thunderbird: If using standard release, upgrade to Thunderbird 148 or later; if using ESR, upgrade to Thunderbird 140.8 or later
  5. Restart the application after upgrading
  6. Verify the installed version matches or exceeds the fixed releases (115.33, 140.8, or 148)

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

Fix this in Firefox Scoped from the published advisory
  • Consultation1.0 h
  • Implementation2.0 h
  • Testing2.0 h
  • Review / QA1.0 h
6.0 hours of engineering $1,040
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,664.

Scan for this in your stack

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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-2026-2775 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