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FirefoxWeb browser · Mozilla

CVE-2025-8027

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
On 64-bit platforms IonMonkey-JIT only wrote 32 bits of the 64-bit return value space on the stack. Baseline-JIT, however, read the entire 64 bits. 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

On 64-bit platforms, the IonMonkey JIT compiler only wrote 32 bits of the 64-bit return value space on the stack, while the Baseline-JIT compiler read the entire 64 bits. This mismatch causes uninitialized or leftover stack data in the upper 32 bits to be consumed, potentially leading to information disclosure or undefined behavior.

MitigationUpdate affected Firefox and Thunderbird installations to the patched versions (Firefox 141+, Firefox ESR 115.26+, Firefox ESR 128.13+, Firefox ESR 140.1+, Thunderbird 141+, Thunderbird 128.13+, Thunderbird 140.1+).

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 installed Firefox version
    Open about:firefox in the address bar or go to Help > About Firefox. Note the version number displayed.
    Affected if The version is less than 115.26.0, or between 128.0.0 and 128.12.x, or between 140.0.0 and 140.0.x, or less than 141.0 on the initial release branch.
  2. Check installed Thunderbird version
    Open About Thunderbird from the Help menu. Note the version number displayed.
    Affected if The version is less than 128.13.0, or between 140.0.0 and 140.0.x, or less than 141.0 on the initial release branch.
  3. Confirm 64-bit platform
    Check the system architecture. On Windows, verify the build is x64 in Help > About or Task Manager. On macOS, check System Report for Intel x86_64 or Apple Silicon. On Linux, run 'uname -m' - x86_64 indicates 64-bit.
    Affected if The system is running a 32-bit (i686, i386) build - the vulnerability only affects 64-bit platforms.
  4. Verify JIT compiler is enabled
    In Firefox, go to about:config and search for 'javascript.options.jit'. The setting 'javascript.options.jit' should be true (enabled by default). IonMonkey is the JIT engine.
    Affected if JIT is explicitly disabled via about:config setting javascript.options.jit set to false - the flaw requires IonMonkey to be active.

A user is affected if they run an affected Firefox or Thunderbird version (pre-115.26.0, pre-128.13.0, pre-140.1.0, or pre-141.0) on a 64-bit platform with JIT compilation enabled (the default state).

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 and Thunderbird installations to the patched versions (Firefox 141+, Firefox ESR 115.26+, Firefox ESR 128.13+, Firefox ESR 140.1+, Thunderbird 141+, Thunderbird 128.13+, Thunderbird 140.1+).

Recommended fix High confidence

Firefox 141 (or ESR 115.26/128.13/140.1 depending on release channel); Thunderbird 141 (or 128.13/140.1 depending on release channel)

  1. Check current Firefox or Thunderbird version via Help > About (or firefox --version / thunderbird --version from command line)
  2. Download the appropriate fixed version from https://www.mozilla.org/en-US/firefox/all/ or https://www.mozilla.org/en-US/thunderbird/all/
  3. Install the new version, which will overwrite the existing installation
  4. Restart the application after installation
  5. Verify the version has been updated to a fixed release (115.26.0+, 128.13.0+, 140.1.0+, or 141.0+)
  6. Enable automatic updates via Settings > Advanced > Update to ensure future security patches are applied
Caveat Major browser updates may occasionally affect extension compatibility or user preferences; review release notes before upgrading if running critical workflows

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
  • Testing1.0 h
  • Review / QA1.0 h
4.0 hours of engineering $750
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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-2025-8027 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