How severe is CVE-2019-17026?

CVE-2019-17026 has a CVSS score of 8.8/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by CVE-2019-17026?

Affected package information for CVE-2019-17026 is not yet fully mapped. Check the official advisory links for details.

How do I fix CVE-2019-17026?

No fixed version has been published for CVE-2019-17026 yet. Monitor the advisory for updates, apply mitigations recommended by the vendor, and use O3 Security to track when a fix becomes available in your stack.

Is CVE-2019-17026 actively exploited in the wild?

Yes. There are 9 known exploit references for CVE-2019-17026, including 1 documented proof-of-concept exploit on Exploit-DB and 6 in-the-wild exploitations observed on GitHub and other sources. Treat this as actively exploitable and prioritize patching immediately. All exploit code should only be run in an isolated sandbox environment for research or authorized testing — never against production systems without explicit written authorization.

What is the EPSS score for CVE-2019-17026?

CVE-2019-17026 has an EPSS (Exploit Prediction Scoring System) score of 56.2%, placing it in the 98th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. A score above 50% indicates significantly elevated exploitation risk — immediate patching is strongly recommended.

Is CVE-2019-17026 in the CISA Known Exploited Vulnerabilities catalog?

Yes. CVE-2019-17026 (Mozilla Firefox And Thunderbird Type Confusion Vulnerability) was added to CISA's Known Exploited Vulnerabilities (KEV) catalog on 2021-11-03. CISA required all US federal civilian agencies to remediate this vulnerability by 2022-05-03. The required action was: Apply updates per vendor instructions. Being listed in the KEV catalog is the strongest possible confirmation of active exploitation — treat this as a critical priority.

When was CVE-2019-17026 published, and has it been updated?

CVE-2019-17026 was published on March 2, 2020 and was last updated on April 16, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

CISA KEV·Added 2021-11-03 — agencies required to remediate by 2022-05-03

CVE-2019-17026

HIGH

Published

Mar 2, 2020

Updated

Apr 16, 2026

Affected

0 pkgs

Patched

None yet

Exploits

9 known

EPSS Exploitation Probability

via FIRST.org ↗

56.2%probability of exploitation in next 30 days

High Risk98th percentile0.00%

EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.

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.

Exploits & PoCs

Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.

EDB-49864localwindows_x86-64

Firefox 72 IonMonkey - JIT Type Confusion

by Forrest Orr · May 13, 2021

Exploit-DB Source

Frequently Asked Questions

O3 Security · Impact-Aware SCA

Is CVE-2019-17026 in your stack?

O3 detects CVE-2019-17026 across dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.

Scan my stack How O3 SCA works