# CVE-2019-17026: Mozilla Firefox And Thunderbird Type Confusion Vulnerability

Source: https://junglewise.ai/threats/cve-2019-17026-mozilla-firefox-and-thunderbird-type-confusion-vulnerability  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2021-11-03. Updated: 2026-05-10  
License: CC BY 4.0 with a link back

CVE-2019-17026 · Severity: critical · CVSS 8.8 · Exploited in the wild · Published 2021-11-03

A type confusion vulnerability exists in the Mozilla IonMonkey JIT compiler due to incorrect alias information when setting array elements. This flaw can be exploited to execute arbitrary code or cause a denial of service when processing malicious web content.

Technologies: [Mozilla Firefox](https://junglewise.ai/threats/technologies/firefox), [Mozilla Thunderbird](https://junglewise.ai/threats/technologies/thunderbird). Vendors: [Mozilla](https://junglewise.ai/threats/vendors/mozilla).

## Quick answers

**Is CVE-2019-17026 exploited in the wild?** Yes. CVE-2019-17026 is known to be exploited in the wild, first recorded on 3 November 2021. Treat it as urgent.

**How severe is CVE-2019-17026?** Critical severity, with a CVSS score of 8.8, published 3 November 2021.

**Which products and versions are affected?** Mozilla Firefox < 72.0.1; Mozilla Firefox ESR < 68.4.1; Mozilla Thunderbird < 68.4.1.

**Is there a fix for CVE-2019-17026?** A patch was published on 2020-01-08: Fixed in Firefox 72.0.1, Firefox ESR 68.4.1, and Thunderbird 68.4.1 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2019-17026 attacked?** It is attacked over the network, in a network appliance.

**Am I affected by CVE-2019-17026?** Check whether you run Mozilla Firefox or Mozilla Thunderbird. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Affected products

- Mozilla Firefox < 72.0.1
- Mozilla Firefox ESR < 68.4.1
- Mozilla Thunderbird < 68.4.1

## Timeline

- 2020-01-08: patched: Fixed in Firefox 72.0.1, Firefox ESR 68.4.1, and Thunderbird 68.4.1
- 2021-11-03: kev added: Added to CISA Known Exploited Vulnerabilities Catalog
- 2021-11-03: disclosed: Publicly disclosed via NVD and CISA KEV catalog
- 2021-11-03: exploited: CISA confirms targeted attacks in the wild abusing this flaw.

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