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FirefoxWeb browser · Mozilla

CVE-2016-5257

CRITICAL · 9.8 CVSS v3.0 Published 2016-09-22
Fix available
A fix is available. Upgrade to after 48.0.2 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
Multiple unspecified vulnerabilities in the browser engine in Mozilla Firefox before 49.0, Firefox ESR 45.x before 45.4 and Thunderbird < 45.4 allow remote attackers to cause a denial of service (memory corruption and application crash) or possibly execute arbitrary code via unknown vectors.

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

Memory corruption vulnerabilities in Mozilla's browser engine (Spidermonkey/Necko) affecting Firefox versions before 49.0 and Firefox ESR/Thunderbird before 45.4. The unspecified vulnerabilities allow remote attackers to trigger memory corruption leading to denial of service or potentially arbitrary code execution.

MitigationUpgrade immediately to Firefox 49.0+, Firefox ESR 45.4+, or Thunderbird 45.4+ to patch the memory corruption vulnerabilities in the browser 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:<= 48.0.2= 45.1.0= 45.1.1= 45.2.0= 45.3.0

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. Check Firefox version
    Open Firefox, click the menu button (three horizontal lines), select Help, then About Firefox. The version number will display in the window that opens.
    Affected if Version is 48.0.2 or lower, OR version is 45.1.0, 45.1.1, 45.2.0, or 45.3.0 (these specific 45.x versions are listed as affected)
  2. Check if running Firefox ESR
    In the About Firefox window, look for 'Mozilla Firefox ESR' in the version string. ESR versions have a different release cycle and are listed separately in the CVE.
    Affected if Running Firefox ESR version 45.3.0 or lower (these are affected per the CVE) - though the CVE specifically notes Firefox ESR before 45.4 as affected
  3. Check if running Thunderbird
    In Thunderbird, go to Help > About Thunderbird to see the version. Thunderbird shares the same browser engine (Spidermonkey/Necko) and is affected by these memory corruption flaws.
    Affected if Running Thunderbird version below 45.4 (the CVE lists Thunderbird before 45.4 as affected)

You are affected if you are running any Firefox version 48.0.2 or below, specific Firefox 45.x versions (45.1.0-45.3.0), Firefox ESR before 45.4, or Thunderbird before 45.4, since these contain the vulnerable browser engine.

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 a release after 48.0.2
Interim mitigation

Upgrade immediately to Firefox 49.0+, Firefox ESR 45.4+, or Thunderbird 45.4+ to patch the memory corruption vulnerabilities in the browser engine.

Recommended fix High confidence

Firefox 49.0 or later (or Firefox ESR 45.4 or later for the ESR 45.x branch)

  1. 1. Back up all bookmarks, saved passwords, and important browser data using the Firefox Sync feature or by backing up the profile folder (typically located at %APPDATA%\Mozilla\Firefox\Profiles on Windows, ~/.mozilla/firefox on Linux, or ~/Library/Application Support/Firefox/Profiles on macOS)
  2. 2. Open Firefox and navigate to Help > About Firefox
  3. 3. In the About Firefox window, click 'Check for Updates' to trigger the update process
  4. 4. If an update is available, Firefox will download and install it automatically
  5. 5. Restart Firefox when prompted to complete the installation
  6. 6. Verify the version by going to Help > About Firefox - it should show 49.0 or later (or 45.4 or later for ESR)
Caveat Users on Firefox 45.x ESR should note that moving to 49.0 is a major version jump; ensure compatibility with any required browser extensions or enterprise policies before upgrading

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

Fix this in Firefox Scoped from the published advisory
  • Consultation2.0 h
  • Implementation2.0 h
  • Testing2.0 h
  • Review / QA1.0 h
7.0 hours of engineering $1,240
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,984.

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-2016-5257 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