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FirefoxWeb browser · Mozilla

CVE-2017-7756

CRITICAL · 9.8 CVSS v3.0 Published 2018-06-11
Fix available
A fix is available. Upgrade to 52.2.0 / 54.0 or later.
See remediation →
100/100
Remediation priority · Urgent
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 use-after-free and use-after-scope vulnerability when logging errors from headers for XML HTTP Requests (XHR). This could result in a potentially exploitable crash. This vulnerability affects Firefox < 54, Firefox ESR < 52.2, and Thunderbird < 52.2.

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 · high confidence

A use-after-free and use-after-scope vulnerability exists in how Mozilla browsers and Thunderbird log errors from XML HTTP Request (XHR) headers. When an XHR request encounters an error, the logging code attempts to access memory that has already been freed or is outside the current scope, leading to memory corruption that could be exploited for arbitrary code execution.

MitigationUpgrade Firefox to version 54 or later, Firefox ESR to 52.2 or later, and Thunderbird to 52.2 or later to patch this memory corruption vulnerability.

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:< 52.2.0< 54.0
Debian LinuxOperating system
Affected:= 8.0= 9.0
ThunderbirdApplication
Affected:< 52.2.0

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
High
Availability
High

CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

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 the installed Mozilla product
    Open the application and navigate to Help > About Firefox or Help > About Thunderbird to view the exact version number
    Affected if The product is Firefox or Thunderbird and the version is below 52.2.0 for ESR variants or below 54.0 for standard releases
  2. Confirm the Firefox release variant
    Check if you are running Firefox ESR by looking at the version string in Help > About Firefox; ESR versions include 'ESR' in the version display
    Affected if Running Firefox ESR version less than 52.2.0
  3. Check the exact version number against affected ranges
    Compare your displayed version number to the affected ranges: Firefox < 52.2.0, Firefox < 54.0 (non-ESR), or Thunderbird < 52.2.0
    Affected if Your installed version falls within any of the affected ranges listed
  4. Determine if the system processes untrusted web content
    Assess whether the browser is used to visit websites or execute JavaScript code, as the vulnerability triggers during XHR error handling when processing web content
    Affected if The browser processes web content with XHR requests that could trigger error conditions

You are affected if you are running Firefox versions below 54.0 (or below 52.2.0 for ESR), or Thunderbird below 52.2.0, and the browser processes web content that can trigger XHR errors.

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 52.2.0 / 54.0 or later
Fixed in 52.2.054.0
Interim mitigation

Upgrade Firefox to version 54 or later, Firefox ESR to 52.2 or later, and Thunderbird to 52.2 or later to patch this memory corruption vulnerability.

Recommended fix High confidence

Firefox 54.0+ / Firefox ESR 52.2+ / Thunderbird 52.2+

  1. Upgrade Firefox to version 54.0 or later (or Firefox ESR 52.2 or later if using ESR)
  2. Upgrade Thunderbird to version 52.2 or later
  3. Restart the browser/application after upgrading

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

Fix this in Firefox Scoped from the published advisory
  • Consultation1.0 h
  • Implementation2.0 h
  • Testing2.0 h
  • Review / QA1.0 h
6.0 hours of engineering $1,040
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,664.

Scan for this in your stack

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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-2017-7756 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