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Actively exploited in the wild. This CVE is on the CISA Known Exploited Vulnerabilities list — treat remediation as urgent. Federal remediation due by 3 May 2022.
FirefoxWeb browser · Mozilla

CVE-2019-17026

HIGH · 8.8 CVSS v3.1 Published 2020-03-02
Fix available
A fix is available. Upgrade to 68.4.1 / 72.0.1 or later.
See remediation →
100/100
Remediation priority · Urgent
In the wild Public exploit Remotely reachable No privileges

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 alias information in IonMonkey JIT compiler for setting array elements could lead to a type confusion. We are aware of targeted attacks in the wild abusing this flaw. This vulnerability affects Firefox ESR < 68.4.1, Thunderbird < 68.4.1, and Firefox < 72.0.1.

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 type confusion vulnerability exists in Mozilla's IonMonkey JIT compiler where incorrect alias information when setting array elements allows an attacker to manipulate JavaScript object types. This can be exploited to execute arbitrary code via the JIT-compiled code path.

MitigationApply vendor-provided patches by updating affected installations to Firefox ESR 68.4.1+, Thunderbird 68.4.1+, or Firefox 72.0.1+ immediately, given confirmed active exploitation in the wild.

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:< 68.4.1< 72.0.1
Ubuntu LinuxOperating system
Affected:= 16.04
ThunderbirdApplication
Affected:< 68.4.1

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
Required
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/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, go to Help > About Firefox, or run 'firefox --version' from command line
    Affected if Version is below 72.0.1 (or below 68.4.1 for ESR releases)
  2. Check Thunderbird version
    Open Thunderbird, go to Help > About Thunderbird, or run 'thunderbird --version' from command line
    Affected if Version is below 68.4.1
  3. Verify IonMonkey JIT is enabled
    In Firefox address bar, type 'about:config', search for 'javascript.options IonMonkey' and check if the value is set to true
    Affected if IonMonkey is enabled (value is true) - the vulnerability exists in the JIT compiler
  4. Check Ubuntu Firefox package version (if on Ubuntu)
    Run 'dpkg -l | grep firefox' or 'apt policy firefox' to see installed package version on Ubuntu 16.04
    Affected if Firefox package version is below the patched version available for Ubuntu 16.04

You are affected if you have Firefox below 72.0.1 (or below 68.4.1 for ESR) or Thunderbird below 68.4.1, AND the IonMonkey JIT compiler is enabled in your browser settings.

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 68.4.1 / 72.0.1 or later
Fixed in 68.4.172.0.1
Interim mitigation

Apply vendor-provided patches by updating affected installations to Firefox ESR 68.4.1+, Thunderbird 68.4.1+, or Firefox 72.0.1+ immediately, given confirmed active exploitation in the wild.

Recommended fix High confidence

Firefox 72.0.1 / Firefox ESR 68.4.1 / Thunderbird 68.4.1

  1. Check current Firefox or Thunderbird version by navigating to Help > About (or running 'firefox --version' / 'thunderbird --version' in terminal)
  2. For Ubuntu 16.04: Run 'sudo apt-get update' followed by 'sudo apt-get install firefox' or 'sudo apt-get install thunderbird' to install the security update
  3. For Windows/macOS: Download Firefox 72.0.1 or later from https://www.mozilla.org/firefox/ or Thunderbird 68.4.1 or later from https://www.thunderbird.net/
  4. For Enterprise deployments: Update to Firefox ESR 68.4.1 or later via your management tooling
  5. Restart the browser/application after upgrade completes
  6. Verify the installed version matches or exceeds the fixed release (Firefox 72.0.1+, Firefox ESR 68.4.1+, Thunderbird 68.4.1+)
Caveat Minor UI changes may occur between major versions; ensure compatibility testing for enterprise add-ons and policies

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

Fix this in Firefox Exploited in the wild — priority engagement
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing3.0 h
  • Review / QA1.0 h
10.0 hours of engineering $1,750
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An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,800.

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-2019-17026 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