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FirefoxWeb browser · Mozilla

CVE-2018-18500

CRITICAL · 9.8 CVSS v3.0 Published 2019-02-05
Fix available
A fix is available. Upgrade to 60.5 / 65.0 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 vulnerability can occur while parsing an HTML5 stream in concert with custom HTML elements. This results in the stream parser object being freed while still in use, leading to a potentially exploitable crash. This vulnerability affects Thunderbird < 60.5, Firefox ESR < 60.5, and Firefox < 65.

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 vulnerability in the HTML5 stream parser of Firefox and Thunderbird allows memory corruption when parsing HTML5 streams with custom HTML elements. The stream parser object is freed while still in use, leading to potential code execution.

MitigationUpgrade to Thunderbird 60.5+, Firefox ESR 60.5+, or Firefox 65+ to patch the vulnerability. No workarounds exist; software update is required.

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:< 65.0
Firefox EsrWeb browser
Affected:< 60.5
Ubuntu LinuxOperating system
Affected:= 14.04= 16.04= 18.04= 18.10
Debian LinuxOperating system
Affected:= 8.0= 9.0
Enterprise Linux DesktopOperating system
Affected:= 6.0= 7.0
Enterprise Linux ServerOperating system
Affected:= 6.0= 7.0
Enterprise Linux Server AusOperating system
Affected:= 7.6
Enterprise Linux Server EusOperating system
Affected:= 7.6

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 installed Firefox version
    Run 'firefox --version' or check package manager: 'dpkg -l | grep firefox' on Debian/Ubuntu, 'rpm -qa | grep -i firefox' on RHEL
    Affected if Version is below 65.0 (e.g., 64.x or earlier)
  2. Identify installed Firefox ESR version
    Run 'firefox --version' or check package manager for ESR variant: 'rpm -qa | grep firefox-esr' on RHEL
    Affected if Version is below 60.5 (e.g., 60.4.x or earlier)
  3. Identify installed Thunderbird version
    Run 'thunderbird --version' or check package manager: 'dpkg -l | grep thunderbird' on Debian/Ubuntu, 'rpm -qa | grep thunderbird' on RHEL
    Affected if Version is below 60.5 (e.g., 60.4.x or earlier)
  4. Check if HTML5 stream parsing is in use
    Inspect browser activity or check for web content using HTML5 streams with custom HTML elements. This is typically triggered when processing HTML5 media streams or custom element definitions in web content.
    Affected if User processes HTML5 streams with custom HTML elements in the affected browser application

A user is affected if they run Firefox below 65.0, Firefox ESR below 60.5, or Thunderbird below 60.5, AND actively use HTML5 stream parsing with custom HTML elements in web content.

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 60.5 / 65.0 or later
Fixed in 60.565.0
Interim mitigation

Upgrade to Thunderbird 60.5+, Firefox ESR 60.5+, or Firefox 65+ to patch the vulnerability. No workarounds exist; software update is required.

Recommended fix High confidence

Firefox 65.0+ / Firefox ESR 60.5+ / Thunderbird 60.5+

  1. Identify the installed Firefox, Firefox ESR, or Thunderbird version by checking About menu or running: firefox --version, thunderbird --version
  2. For Firefox: Upgrade to version 65.0 or later
  3. For Firefox ESR: Upgrade to version 60.5 or later
  4. For Thunderbird: Upgrade to version 60.5 or later
  5. On Linux systems (Ubuntu, Debian, Enterprise Linux): Run system package manager update (e.g., sudo apt-get update && sudo apt-get upgrade for Debian/Ubuntu, or sudo yum update for RHEL/CentOS)
  6. Restart the application after update completes
  7. Verify the installed version is at or above the fixed release
Caveat Minor version upgrades typically maintain compatibility; however, some older extensions or plugins may require updates

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

Fix this in Firefox Scoped from the published advisory
  • Consultation3.0 h
  • Implementation6.0 h
  • Testing3.0 h
  • Review / QA2.0 h
14.0 hours of engineering $2,490
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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-2018-18500 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