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FirefoxWeb browser · Mozilla

CVE-2025-4918

CRITICAL · 9.8 CVSS v3.1 Published 2025-05-17
Fix available
A fix is available. Upgrade to 115.23.1 / 128.10.1 or later.
See remediation →
100/100
Remediation priority · Urgent
Public exploit 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
An attacker was able to perform an out-of-bounds read or write on a JavaScript `Promise` object. This vulnerability was fixed in Firefox 138.0.4, Firefox ESR 128.10.1, Firefox ESR 115.23.1, Thunderbird 128.10.2, and Thunderbird 138.0.2.

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
How this class of weakness works · CWE-125

The code reads past the end (or before the start) of a buffer, returning memory that was never meant to be exposed. Attackers use it to leak secrets like keys or to defeat memory-protection defences. Remediation is validating indices and lengths before every read.

General guidance for the out-of-bounds read class — the official description and references above are authoritative for this specific CVE. Want a bespoke review and a reviewed fix? Ask our team →

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:< 115.23.1< 138.0.4>= 116.0, < 128.10.1
ThunderbirdApplication
Affected:< 128.10.2>= 138.0, < 138.0.2

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

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 115.23.1 / 128.10.1 / 128.10.2 or later
Fixed in 115.23.1128.10.1128.10.2
Recommended fix High confidence

Firefox ESR 115.23.1, Firefox ESR 128.10.1, Firefox 138.0.4, Thunderbird 128.10.2, or Thunderbird 138.0.2 (depending on current release channel)

  1. 1. Identify the currently installed Firefox or Thunderbird version via Help > About (or running 'firefox --version' / 'thunderbird --version' in terminal)
  2. 2. If running Firefox 115.x (ESR), upgrade to Firefox ESR 115.23.1 or later
  3. 3. If running Firefox 116.0-128.x (standard release), upgrade to Firefox 138.0.4 or later
  4. 4. If running Firefox 128.x ESR, upgrade to Firefox ESR 128.10.1 or later
  5. 5. If running Thunderbird 128.x, upgrade to Thunderbird 128.10.2 or later
  6. 6. If running Thunderbird 138.x, upgrade to Thunderbird 138.0.2 or later
  7. 7. Restart the application after upgrade and verify the version in Help > About
Caveat Mozilla minor version upgrades typically have low risk; however, some older extensions or add-ons may be incompatible with newer major versions

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

We can perform the upgrade in your staging environment and verify nothing breaks — typical engagement from $3,550. Get the upgrade done

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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-2025-4918 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