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FirefoxWeb browser · Mozilla

CVE-2026-2793

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
Memory safety bugs present in Firefox ESR 115.32, Firefox ESR 140.7, Thunderbird ESR 140.7, Firefox 147 and Thunderbird 147. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. 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

Memory safety bugs in Firefox ESR and Thunderbird allowed memory corruption that could potentially be exploited for arbitrary code execution. The vulnerability affects multiple product versions (Firefox 147, Thunderbird 147, and ESR versions 115.32 and 140.7) and was addressed through updated patched versions.

MitigationUpdate affected software to Firefox 148, Firefox ESR 115.33/140.8, Thunderbird 148/140.8 or later versions to remediate the memory corruption 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:< 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
    In Firefox, go to Menu > Help > About Firefox. The version number is displayed on this page.
    Affected if The displayed version is less than 115.33.0, OR is 128.0 or higher but less than 140.8.0, OR is less than 148.0 (for non-ESR releases that bypassed the other ranges)
  2. Check installed Thunderbird version
    In Thunderbird, go to Menu > Help > About Thunderbird. The version number is displayed on this page.
    Affected if The displayed version is less than 140.8.0, OR is less than 148.0
  3. Verify Firefox ESR version if applicable
    In Firefox ESR, go to Menu > Help > About Firefox. ESR versions are typically labeled (for example, '115.33.0 (64-bit) ESR').
    Affected if The ESR version is less than 115.33.0 OR is less than 140.8.0
  4. Confirm application type via command line
    On Windows: Run 'firefox --version' or 'thunderbird --version' from command prompt. On macOS: Run '/Applications/Firefox.app/Contents/MacOS/firefox --version' or similar path.
    Affected if The version output matches the affected ranges above (not 115.33+, 140.8+, or 148+)

You are affected if you are running any version of Firefox or Thunderbird that is not 115.33.0 or higher (ESR), 140.8.0 or higher, or 148.0 or higher.

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 affected software to Firefox 148, Firefox ESR 115.33/140.8, Thunderbird 148/140.8 or later versions to remediate the memory corruption vulnerability.

Recommended fix High confidence

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

  1. Check current Firefox or Thunderbird version: Menu > Help > About (or run: firefox --version / thunderbird --version)
  2. Identify the product and release track (Firefox Stable, Firefox ESR, or Thunderbird)
  3. For Firefox Stable users: Upgrade to Firefox 148 or later
  4. For Firefox ESR 115.x users: Upgrade to Firefox ESR 115.33 or later
  5. For Firefox ESR 140.x users: Upgrade to Firefox ESR 140.8 or later
  6. For Thunderbird users: Upgrade to Thunderbird 140.8 or later (or Thunderbird 148)
  7. Restart the application after upgrade and verify the version in Help > About
Caveat Standard Mozilla minor version upgrades typically have no breaking changes; always back up profiles before major upgrades

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
  • Testing2.0 h
  • Review / QA1.0 h
6.0 hours of engineering $1,060
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,696.

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-2026-2793 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