CVE-2019-17026VulnerabilityPublished 11/03/2021Updated 10/24/2026

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

Affects Mozilla Firefox and ThunderbirdSource CISA KEV

Severity

High

No CVSS score published yet

Exploitation: Actively exploited – in CISA KEV since 11/03/2021
KEV deadline: 05/03/2022
EPSS: 46.3% chance of exploitation in 30 days – higher than 98% of CVEs

What to do

CISA required action

Apply updates per vendor instructions.

nvd.nist.gov/vuln/detail/CVE-2019-17026 (opens in a new tab)

Description

CVE-2019-17026 is a high severity type confusion vulnerability in Mozilla Firefox and Thunderbird. It arises from incorrect alias information in the IonMonkey JIT compiler when setting array elements. This flaw has been exploited in the wild. No specific affected versions or patch information is provided in the available data.

Summary

Mozilla Firefox and Thunderbird contain a type confusion vulnerability (CVE-2019-17026) caused by incorrect alias information in the IonMonkey Just-In-Time (JIT) compiler during array element assignment. This vulnerability can lead to memory corruption or other unexpected behavior due to type confusion. The vulnerability has been observed to be exploited in the wild, indicating active threat usage. However, no explicit patch or remediation details are provided in the current data.

Impact

Exploitation of this vulnerability can lead to potential memory corruption or arbitrary code execution due to type confusion in the JIT compiler. The fact that it has been exploited in the wild confirms its practical impact on affected users of Firefox and Thunderbird. The exact impact depends on exploitation context but is considered high severity.

Mitigation

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Users and administrators should monitor Mozilla's official security advisories for updates and apply any available patches promptly once released.

Weaknesses

CWE-843Type Confusion (opens in a new tab)

What to do

Description

AnalysisAI-generated, updated 10/24/2026, 09:10:16 UTC

Weaknesses

References

Related threats