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FirefoxWeb browser · Mozilla

CVE-2026-6772

HIGH · 7.5 CVSS v3.1 Published 2026-04-21
Fix available
A fix is available. Upgrade to 115.35.0 / 140.10.0 or later.
See remediation →
84/100
Remediation priority · High
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
Incorrect boundary conditions in the Libraries component in NSS. This vulnerability was fixed in Firefox 150, Firefox ESR 115.35, Firefox ESR 140.10, Thunderbird 150, and Thunderbird 140.10.

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 · moderate confidence

Incorrect boundary conditions in the NSS (Network Security Services) Libraries component. Boundary condition errors typically involve improper validation of array bounds, buffer limits, or memory offsets, which can lead to out-of-bounds memory access and potential memory corruption during cryptographic operations.

MitigationApply the security updates for Firefox 150, Firefox ESR 115.35/140.10, or Thunderbird 140.10/150 as appropriate. For standalone NSS usage, obtain the patched NSS library version corresponding to these releases.

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:< 115.35.0< 150.0>= 140.0, < 140.10.0
ThunderbirdApplication
Affected:< 140.10.0

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
None
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/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. Identify installed Mozilla product
    Check if Firefox or Thunderbird is installed on the system. On Windows, look in Program Files. On macOS, check /Applications. On Linux, check package manager or /usr/lib/firefox or /usr/lib/thunderbird.
    Affected if Neither Firefox nor Thunderbird is installed, then this CVE does not apply.
  2. Determine Firefox version
    In Firefox, go to Help > About Firefox, or check the application binary/version file. On Linux, run: firefox --version
    Affected if Firefox version is less than 115.35.0, OR between 140.0 and 140.10.0 exclusive, OR less than 150.0.
  3. Determine Thunderbird version
    In Thunderbird, go to Help > About Thunderbird, or check the application binary/version file. On Linux, run: thunderbird --version
    Affected if Thunderbird version is less than 140.10.0.
  4. Verify NSS library version (standalone usage)
    If NSS is used standalone (not through Firefox/Thunderbird), check the NSS library version. On Linux: pkg-config --modversion nss3 or check libnss3.so version. On Windows: check nss3.dll properties.
    Affected if NSS library version corresponds to unpatched Firefox 115.35/140.10 or Thunderbird 140.10/150 releases.

The environment is affected if Firefox version is less than 115.35.0, less than 150.0, or between 140.0 and 140.10.0; or if Thunderbird version is less than 140.10.0; or if standalone NSS library matches unpatched versions.

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 115.35.0 / 140.10.0 / 150.0 or later
Fixed in 115.35.0140.10.0150.0
Interim mitigation

Apply the security updates for Firefox 150, Firefox ESR 115.35/140.10, or Thunderbird 140.10/150 as appropriate. For standalone NSS usage, obtain the patched NSS library version corresponding to these releases.

Recommended fix High confidence

Firefox 150 / Firefox ESR 115.35.0 / Firefox ESR 140.10.0 / Thunderbird 150 / Thunderbird 140.10.0

  1. 1. Determine if you are running Firefox or Thunderbird, and whether it is the standard release or Extended Support Release (ESR)
  2. 2. For Firefox standard users: Upgrade to Firefox 150 or later
  3. 3. For Firefox ESR 115.x users: Upgrade to Firefox ESR 115.35.0 or later
  4. 4. For Firefox ESR 140.x users: Upgrade to Firefox ESR 140.10.0 or later
  5. 5. For Thunderbird standard users: Upgrade to Thunderbird 150 or later
  6. 6. For Thunderbird 140.x users: Upgrade to Thunderbird 140.10.0 or later
  7. 7. Download the appropriate version from the official Mozilla website (www.mozilla.org)
  8. 8. Install the update following standard installation procedures

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

Fix this in Firefox Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing3.0 h
  • Review / QA2.0 h
11.0 hours of engineering $1,930
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $3,088.

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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-2026-6772 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