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FirefoxWeb browser · Mozilla

CVE-2026-2787

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
Use-after-free in the DOM: Window and Location 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 · high confidence

Use-after-free vulnerability in the DOM Window and Location component in Firefox and Thunderbird allows remote attackers to potentially execute arbitrary code via crafted HTML content by freeing memory and then accessing the freed memory location.

MitigationUpdate Firefox to version 148 or later, Firefox ESR to 115.33/140.8 or later, and Thunderbird to version 148/140.8 or later to obtain the security patch.

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. Identify installed product
    Open browser/application and navigate to Help > About (Firefox) or Help > About Thunderbird to display the version number, or run: firefox --version or thunderbird --version
    Affected if Product is Mozilla Firefox or Thunderbird
  2. Check Firefox version against affected ranges
    If Firefox is installed, compare your version to: < 115.33.0, OR >= 128.0 AND < 140.8.0, OR < 148.0. In practical terms, any Firefox version below 148.0 is likely affected.
    Affected if Firefox version is below 148.0 (or below 115.33.0 for old ESR, or below 140.8.0 for ESR 128.x)
  3. Check Thunderbird version against affected ranges
    If Thunderbird is installed, compare your version to: < 140.8.0 OR < 148.0. Any version below 148.0 is affected.
    Affected if Thunderbird version is below 148.0 (and specifically below 140.8.0 for older ESR branches)

If either Firefox or Thunderbird is installed and the version falls below the safe thresholds (148.0 for current, 140.8.0 for ESR, 115.33.0 for old ESR), the environment is affected by this use-after-free vulnerability in the DOM Window and Location component.

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

Update Firefox to version 148 or later, Firefox ESR to 115.33/140.8 or later, and Thunderbird to version 148/140.8 or later to obtain the security patch.

Recommended fix High confidence

Firefox 148.0 / Firefox ESR 115.33.0 / Firefox ESR 140.8.0 / Thunderbird 148.0 / Thunderbird 140.8.0 (depending on product and release channel)

  1. 1. Identify the current Firefox or Thunderbird version by navigating to Help > About (or using menu > Help > About)
  2. 2. Determine which release channel is in use: standard release, ESR 115.x, or ESR 140.x
  3. 3. For standard Firefox release: upgrade to version 148.0 or later
  4. 4. For Firefox ESR 115.x: upgrade to version 115.33.0 or later
  5. 5. For Firefox ESR 140.x: upgrade to version 140.8.0 or later
  6. 6. For standard Thunderbird: upgrade to version 148.0 or later
  7. 7. For Thunderbird ESR: upgrade to version 140.8.0 or later
  8. 8. Restart the application after upgrade
Caveat Standard upgrade with no expected breaking changes; minor extension compatibility issues may occur but are rare

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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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-2026-2787 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