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FirefoxWeb browser · Mozilla

CVE-2019-9795

CRITICAL · 9.8 CVSS v3.0 Published 2019-04-26
Fix available
A fix is available. Upgrade to 60.6 / 66.0 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 vulnerability where type-confusion in the IonMonkey just-in-time (JIT) compiler could potentially be used by malicious JavaScript to trigger a potentially exploitable crash. This vulnerability affects Thunderbird < 60.6, Firefox ESR < 60.6, and Firefox < 66.

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

Type-confusion vulnerability in Mozilla's IonMonkey just-in-time (JIT) compiler where malicious JavaScript can cause the JIT engine to make incorrect type assumptions, leading to memory corruption and a potentially exploitable crash.

MitigationUpdate affected Mozilla products to patched versions: Thunderbird and Firefox ESR to >=60.6, Firefox to >=66. This is a critical severity vulnerability in the JIT compiler that could enable arbitrary code execution.

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:< 66.0
Firefox EsrWeb browser
Affected:< 60.6
ThunderbirdApplication
Affected:< 60.6

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. Check Mozilla Firefox version
    Open Firefox and navigate to about:support, or go to Help > About Firefox. The version number is displayed at the top.
    Affected if The version shown is less than 66.0 (for example, 65.x or earlier)
  2. Check Mozilla Firefox ESR version
    Open Firefox ESR and navigate to about:support, or go to Help > About Firefox ESR. The version number is displayed at the top.
    Affected if The version shown is less than 60.6 (for example, 60.5.x or earlier)
  3. Check Mozilla Thunderbird version
    Open Thunderbird and navigate to Help > About Thunderbird. The version number is displayed in the dialog window.
    Affected if The version shown is less than 60.6 (for example, 60.5.x or earlier)
  4. Verify IonMonkey JIT compiler is enabled (optional context)
    In Firefox, type about:config in the address bar, search for javascript.options.ion, and confirm the value is true. This is the default setting.
    Affected if IonMonkey is enabled (default true). The vulnerability only affects systems where JIT compilation is active.

You are affected if any of Firefox (<66.0), Firefox ESR (<60.6), or Thunderbird (<60.6) are installed and IonMonkey JIT is enabled (default).

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 60.6 / 66.0 or later
Fixed in 60.666.0
Interim mitigation

Update affected Mozilla products to patched versions: Thunderbird and Firefox ESR to >=60.6, Firefox to >=66. This is a critical severity vulnerability in the JIT compiler that could enable arbitrary code execution.

Recommended fix High confidence

Firefox 66.0, Firefox ESR 60.6, or Thunderbird 60.6 (depending on product)

  1. Identify which Mozilla product is affected (Firefox, Firefox ESR, or Thunderbird)
  2. Check the current installed version (Help > About Firefox/Thunderbird)
  3. If running Firefox < 66.0, Firefox ESR < 60.6, or Thunderbird < 60.6, the system is vulnerable
  4. Download the fixed version from the official Mozilla website (www.mozilla.org) or your organization's software distribution channel
  5. Close all instances of the affected application
  6. Install the appropriate fixed version: Firefox 66.0, Firefox ESR 60.6, or Thunderbird 60.6
  7. Restart the application and verify the version number matches or exceeds the fixed release
  8. Ensure automatic updates are enabled to receive future security patches
Caveat Major browser upgrades may have compatibility implications with older extensions or plugins; test critical workflows after upgrade

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

Fix this in Firefox Scoped from the published advisory
  • Consultation3.0 h
  • Implementation2.0 h
  • Testing2.0 h
  • Review / QA1.0 h
8.0 hours of engineering $1,440
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,304.

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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-2019-9795 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