Security Resilience

CVE-2019-17026

Memory Safety in Mozilla Firefox ≤ 68.4.1

CISA KEVActive ExploitationEUVD ExploitedPublic PoCMemory Safety
Published
02 March 2020
Modified
04 November 2025
KEV Added
03 November 2021
Patch / advisory
View advisory
CVSS Score v3.1 8.8
Click a component to see what it means
Raw vectorCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
EPSS Score 0.46 99th percentile
Risk Priority 90 floored blend · peak EPSS

CVSS and EPSS are reproduced from their sources (NVD, FIRST EPSS). Risk Priority is our own derived reading, not an NVD score.

Summary

CVE-2019-17026 is a high-severity Type Confusion (CWE-843) vulnerability in Mozilla Firefox. Its CVSS base score is 8.8 (High).

Operationally, exploitation aligns with the MITRE ATT&CK technique Junk Data (T1001.001); ranked in the top 1% of CVEs by exploit likelihood; CISA has added it to the Known Exploited Vulnerabilities catalog; a public proof-of-concept is referenced.

Deeper analysis AI-assisted summary

Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.

The vulnerability CVE-2019-17026 is a type confusion flaw (CWE-843) caused by incorrect alias information in Mozilla's IonMonkey JIT compiler when setting array elements. It affects Firefox versions prior to 72.0.1, Firefox ESR versions prior to 68.4.1, and Thunderbird versions prior to 68.4.1, and carries a CVSS 3.1 score of 8.8.

An attacker can trigger the flaw by serving a malicious web page that causes the JIT compiler to mis-track object types, enabling subsequent memory corruption. Successful exploitation grants arbitrary code execution in the context of the browser process; the issue has already been used in targeted attacks observed in the wild.

Mozilla's security advisory MFSA2020-03 and downstream notices from Ubuntu (USN-4335-1) and Gentoo (GLSA-202003-02) state that the only mitigation is to upgrade to the patched releases (Firefox 72.0.1 / ESR 68.4.1 and Thunderbird 68.4.1). No configuration workarounds are provided.

Packet Storm has published a public proof-of-concept that reproduces the type confusion in IonMonkey.

EU & UK References

Vulnerability Data

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…

more

Firefox < 72.0.1.

CWE(s)
CWE-843
KEV Date Added
03 November 2021

Related Threats

MITRE ATT&CK Enterprise Techniques

T1001.001 Junk Data Command And Control
Adversaries may add junk data to protocols used for command and control to make detection more difficult.
attack.mitre.org →
T1003 OS Credential Dumping Credential Access
Adversaries may attempt to dump credentials to obtain account login and credential material, normally in the form of a hash or a clear text password.
attack.mitre.org →
T1003.005 Cached Domain Credentials Credential Access
Adversaries may attempt to access cached domain credentials used to allow authentication to occur in the event a domain controller is unavailable.
attack.mitre.org →
T1003.006 DCSync Credential Access
Adversaries may attempt to access credentials and other sensitive information by abusing a Windows Domain Controller's application programming interface (API)(Citation: Microsoft DRSR Dec 2017) (Citation: Microsoft GetNCCChanges) (Citati…
attack.mitre.org →
T1005 Data from Local System Collection
Adversaries may search local system sources, such as file systems, configuration files, local databases, virtual machine files, or process memory, to find files of interest and sensitive data prior to Exfiltration.
attack.mitre.org →
T1011.001 Exfiltration Over Bluetooth Exfiltration
Adversaries may attempt to exfiltrate data over Bluetooth rather than the command and control channel.
attack.mitre.org →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2019-11707Same product: Mozilla Firefoxboth on KEV
CVE-2020-6819Same product: Mozilla Firefoxboth on KEV
CVE-2026-74956Same product: Mozilla Firefox
CVE-2026-16355Same product: Mozilla Firefox
CVE-2026-16410Same product: Mozilla Firefox
CVE-2025-14325Same product: Mozilla Firefox
CVE-2026-2796Same product: Mozilla Firefox
CVE-2026-16392Same product: Mozilla Firefox
CVE-2026-2783Same product: Mozilla Firefox
CVE-2026-16363Same product: Mozilla Firefox

Affected Assets

mozilla
firefox
≤ 68.4.1 · ≤ 72.0.1
mozilla
thunderbird
≤ 68.4.1
canonical
ubuntu linux
16.04

Mitigating Controls

Control response

Prevent
Stop it (NIST 800-53)

—

Detect
Catch it (NIST detect / respond)

—

Harden
Shrink the surface (DISA STIG)

—

Validate
Prove the fix (OWASP ASVS)
  • V1.5.2
  • V15.3.5

Mitigating Controls (NIST CSF 2.0) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.

PR.PS-06 partial match
blocks

Secure SDLC practices directly prevent type-confusion flaws via safe typing, static analysis, and code review while the control itself addresses many additional weaknesses.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

A.5.14 Information transfer partial match
removes
A.5.15 Access control partial match
removes
A.5.16 Identity management partial match
removes
A.5.17 Authentication information partial match
removes
A.5.18 Access rights partial match
removes
A.8.10 Information deletion partial match
removes

References