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FirefoxWeb browser · Mozilla

CVE-2025-1013

MEDIUM · 6.5 CVSS v3.1 Published 2025-02-04
Fix available
A fix is available. Upgrade to 128.7.0 / 135.0 or later.
See remediation →
74/100
Remediation priority · Elevated
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
A race condition could have led to private browsing tabs being opened in normal browsing windows. This could have resulted in a potential privacy leak. This vulnerability was fixed in Firefox 135, Firefox ESR 128.7, Thunderbird 128.7, and Thunderbird 135.

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

This is a race condition vulnerability in Firefox and Thunderbird where private browsing tabs could incorrectly be opened in normal browsing windows instead of in an isolated private browsing context. Due to the timing issue, the privacy protections of private browsing mode (no history, no cookies, etc.) could be bypassed, potentially leaking private browsing activity to normal browser history or persistence layers.

MitigationUpgrade to Firefox 135, Firefox ESR 128.7, Thunderbird 128.7, or Thunderbird 135 to obtain the patched version. Alternatively, avoid using private browsing mode until the update is applied.

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:< 128.7.0< 135.0
ThunderbirdApplication
Affected:< 128.7.0>= 129.0, < 135.0

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
Low
Integrity
Low
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/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 installed Firefox version
    In Firefox, go to Menu > Help > About Firefox, or navigate to about:support. Locate the 'Version' field.
    Affected if Version is below 128.7.0 or below 135.0 (for example, 128.6.x, 134.x, etc.)
  2. Check installed Thunderbird version
    In Thunderbird, go to Menu > Help > About Thunderbird. Locate the 'Version' field.
    Affected if Version is below 128.7.0, or is 129.0 through 134.x inclusive.
  3. Determine if private browsing feature is used
    Check whether any user profiles on this installation have ever used Private Browsing mode (Ctrl+Shift+P / Cmd+Shift+P in Firefox, or equivalent). Inspect recent browsing history for entries that should not exist if private browsing worked correctly.
    Affected if Private browsing mode was used on affected versions - the vulnerability allows private browsing history to leak into normal history.
  4. Inspect browsing history for anomalies
    Open the Firefox Library > History panel (Ctrl+H / Cmd+Y). Search for URLs that should not appear if private browsing was functioning correctly - these would be visits that occurred during private sessions but are now visible in normal history.
    Affected if Private browsing URLs appear in normal browser history, indicating the vulnerability was triggered.

A user is affected if they run Firefox below 128.7.0 or below 135.0 (or Thunderbird in the specified vulnerable ranges) AND have used private browsing mode, with private session history incorrectly appearing in normal history.

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 128.7.0 / 135.0 or later
Fixed in 128.7.0135.0
Interim mitigation

Upgrade to Firefox 135, Firefox ESR 128.7, Thunderbird 128.7, or Thunderbird 135 to obtain the patched version. Alternatively, avoid using private browsing mode until the update is applied.

Recommended fix High confidence

Firefox 135 (or Firefox ESR 128.7); Thunderbird 135 (or Thunderbird 128.7)

  1. 1. Check current Firefox version by navigating to about:support or going to Help > About Firefox
  2. 2. Check current Thunderbird version by navigating to Help > About Thunderbird
  3. 3. For Firefox: Download Firefox 135 from mozilla.org or click 'Refresh Firefox' in about:support to get the latest version
  4. 4. For Thunderbird: Download Thunderbird 135 (or 128.7 for extended support) from mozilla.org
  5. 5. Restart the application after installation completes
  6. 6. For Enterprise deployments using Firefox ESR: Deploy Firefox ESR 128.7 as per organizational patching schedule
Caveat Mozilla releases typically do not introduce breaking changes for end users; some legacy extensions/add-ons may need updates for version 135

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

Fix this in Firefox Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing6.0 h
  • Review / QA4.0 h
22.0 hours of engineering $3,860
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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-2025-1013 in production — separate from our analysis above.

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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