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FirefoxWeb browser · Mozilla

CVE-2025-8033

MEDIUM · 6.5 CVSS v3.1 Published 2025-07-22
Fix available
A fix is available. Upgrade to 115.26.0 / 128.13.0 or later.
See remediation →
72/100
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
The JavaScript engine did not handle closed generators correctly and it was possible to resume them leading to a nullptr deref. This vulnerability was fixed in Firefox 141, Firefox ESR 115.26, Firefox ESR 128.13, Firefox ESR 140.1, Thunderbird 141, Thunderbird 128.13, and Thunderbird 140.1.

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

A nullptr dereference vulnerability exists in the SpiderMonkey JavaScript engine where closed generators can be incorrectly resumed, leading to a null pointer dereference. This memory safety issue in the JavaScript engine could potentially be exploited for denial of service or potentially arbitrary code execution.

MitigationUpdate affected Firefox or Thunderbird installations to the fixed versions (Firefox 141, Firefox ESR 115.26/128.13/140.1, Thunderbird 141/128.13/140.1 or later) to remediate the vulnerable JavaScript engine.

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:< 115.26.0< 141.0>= 128.0, < 128.13.0>= 140.0, < 140.1.0
ThunderbirdApplication
Affected:< 128.13.0< 141.0>= 140.0, < 140.1.0

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
Required
Scope
Unchanged
Confidentiality
High
Integrity
None
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/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 if Mozilla Firefox is installed
    Run 'firefox --version' from command line, or on Windows check C:\Program Files\Mozilla Firefox\firefox.exe properties, or open Firefox and go to Menu > Help > About Firefox
    Affected if Firefox version falls into any of these ranges: < 115.26.0, >= 128.0 and < 128.13.0, >= 140.0 and < 140.1.0, or < 141.0 (meaning any version before 141.0 that is not explicitly listed as fixed)
  2. Check if Mozilla Thunderbird is installed
    Run 'thunderbird --version' from command line, or on Windows check C:\Program Files\Mozilla Thunderbird\thunderbird.exe properties, or open Thunderbird and go to Menu > Help > About Thunderbird
    Affected if Thunderbird version falls into any of these ranges: < 128.13.0, >= 140.0 and < 140.1.0, or < 141.0 (meaning any version before 141.0 that is not explicitly listed as fixed)
  3. Verify JavaScript engine is enabled (required for exploit)
    In Firefox/Thunderbird, go to about:config and search for 'javascript.enabled' - this setting controls whether the SpiderMonkey JavaScript engine is active
    Affected if javascript.enabled is set to true (default) - the vulnerability only applies when the JavaScript engine is enabled

You are affected if you have Firefox or Thunderbird installed with a version number lower than the fixed releases (141.0, 140.1.0, 128.13.0, or 115.26.0 depending on your release track), with JavaScript engine enabled.

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 115.26.0 / 128.13.0 / 140.1.0 or later
Fixed in 115.26.0128.13.0140.1.0
Interim mitigation

Update affected Firefox or Thunderbird installations to the fixed versions (Firefox 141, Firefox ESR 115.26/128.13/140.1, Thunderbird 141/128.13/140.1 or later) to remediate the vulnerable JavaScript engine.

Recommended fix High confidence

Firefox 141.0 or later; Firefox ESR 115.26 or later; Firefox ESR 128.13 or later; Firefox ESR 140.1 or later; Thunderbird 128.13 or later; Thunderbird 140.1 or later; Thunderbird 141.0 or later

  1. Open Firefox or Thunderbird
  2. Click the menu button (three horizontal lines) and select Help > About Firefox/Thunderbird
  3. The About window will show the current version and check for updates automatically
  4. If an update is available, click 'Restart to update Firefox/Thunderbird' to apply it
  5. After restarting, verify the version by returning to Help > About to confirm the update installed successfully

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

Fix this in Firefox Scoped from the published advisory
  • Consultation1.0 h
  • Implementation1.0 h
  • Testing2.0 h
  • Review / QA1.0 h
5.0 hours of engineering $860
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-2025-8033 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