VulnTideExploited vulnerabilities, by vendor. Data as of .
Known exploitedIn CISA's KEV catalog since Ransomware use: unknown
Mozilla Firefox and Thunderbird

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

Is it exploited?

Yes. CISA added it to the Known Exploited Vulnerabilities catalog on , 611 days after the CVE record was published.

How likely is exploitation in the next 30 days?
46.3%

EPSS score, percentile 98.8 of all scored records

How severe?
8.8 High

CVSS v3.1 base score, from CISA's enrichment of the record

What should I do?

CISA deadline . Apply updates per vendor instructions.

Advisories and patches (2)

Which versions are affected?

Affected

  • before 68.4.1
  • before 68.4.1
  • before 72.0.1

Versions by product

Source: CISA Known Exploited Vulnerabilities (KEV) catalog, 2026.10.28, as of ; FIRST Exploit Prediction Scoring System (EPSS), v2026.06.15, as of ; CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of . About the data.

What to do

Required action, set by CISA

Apply updates per vendor instructions.

CISA due date for this action: .

Advisories and patches

Linked from CISA's catalog entry

Affected products and versions

As listed in the CVE record.

Mozilla Firefox ESR
StatusVersions
Affectedbefore 68.4.1
Mozilla Thunderbird
StatusVersions
Affectedbefore 68.4.1
Mozilla Firefox
StatusVersions
Affectedbefore 72.0.1

Source: CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of . About the data.

About this vulnerability

Mozilla Firefox and Thunderbird contain a type confusion vulnerability due to incorrect alias information in the IonMonkey JIT compiler when setting array elements.

Summary: CISA's KEV catalog, as of .

  • CISA added CVE-2019-17026 to its Known Exploited Vulnerabilities (KEV) catalog on 3 Nov 2021.
  • CISA's ransomware flag for this entry is "Unknown": no evidence of ransomware use in the catalog, which is not proof of none.
  • The due date CISA sets for the required action is 3 May 2022.
  • The CVE record was published on 2 Mar 2020, 611 days before it was added to KEV.
  • The CVE record carries a CVSS v3.1 base score of 8.8 (High), taken from CISA's enrichment of the record.
  • FIRST's EPSS model puts the probability of exploitation in the next 30 days at 46.3% (percentile 98.8), as of 28 Oct 2026.
  • CISA's SSVC assessment in the CVE record: exploitation active, automatable no, technical impact total.

Source: CISA Known Exploited Vulnerabilities (KEV) catalog, 2026.10.28, as of ; CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of ; FIRST Exploit Prediction Scoring System (EPSS), v2026.06.15, as of . About the data.

Description

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.

Source: CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of . About the data.

Weakness

  • CWE-843: Access of Resource Using Incompatible Type ('Type Confusion')

CWE and CAPEC are maintained by MITRE; the entries are those named in the CVE record and the KEV entry.

Timeline

DateEvent
CVE record published
Added to CISA KEV
CISA due date for the required action
CVE record last updated

References

More exploited Mozilla vulnerabilities

  • CVE-2010-3765: Mozilla Multiple Products Remote Code Execution Vulnerability (added )
  • CVE-2024-9680: Mozilla Firefox Use-After-Free Vulnerability (added )
  • CVE-2016-9079: Mozilla Firefox, Firefox ESR, and Thunderbird Use-After-Free Vulnerability (added )
  • CVE-2015-4495: Mozilla Firefox Security Feature Bypass Vulnerability (added )
  • CVE-2019-11707: Mozilla Firefox and Thunderbird Type Confusion Vulnerability (added )
  • CVE-2019-11708: Mozilla Firefox and Thunderbird Sandbox Escape Vulnerability (added )