Cyber 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 0.44 99th percentile
Risk Priority 90 floored blend · peak EPSS

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 Exploitation for Privilege Escalation (T1068); 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

T1068 Exploitation for Privilege Escalation Privilege Escalation
Adversaries may exploit software vulnerabilities in an attempt to elevate privileges.
attack.mitre.org →
T1190 Exploit Public-Facing Application Initial Access
Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network.
attack.mitre.org →
T1203 Exploitation for Client Execution Execution
Adversaries may exploit software vulnerabilities in client applications to execute code.
attack.mitre.org →
T1210 Exploitation of Remote Services Lateral Movement
Adversaries may exploit remote services to gain unauthorized access to internal systems once inside of a network.
attack.mitre.org →
T1212 Exploitation for Credential Access Credential Access
Adversaries may exploit software vulnerabilities in an attempt to collect credentials.
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-2026-16355Same product: Mozilla Firefox
CVE-2025-14325Same product: Mozilla Firefox
CVE-2020-6819Same product: Mozilla Firefoxboth on KEV
CVE-2026-16410Same product: Mozilla Firefox
CVE-2026-2796Same product: Mozilla Firefox
CVE-2022-26486Same product: Mozilla Firefoxboth on KEV
CVE-2022-26485Same product: Mozilla Firefoxboth on KEV
CVE-2019-11708Same product: Mozilla Firefoxboth on KEV
CVE-2010-3765Same product: Mozilla Firefoxboth on KEV

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
  • V3.2.3
  • 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 mostly match
prevents

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.8.29 Security testing in development and acceptance mostly match
finds

Security testing in development can detect type-confusion vulnerabilities through fuzzing and static analysis.

A.8.25 Secure development life cycle partial match
prevents

Secure SDLC mandates type-safe design and review that can catch type-confusion flaws.

A.8.26 Application security requirements partial match
prevents

Application security requirements can specify strong typing and interface contracts that reduce type confusion.

A.8.27 Secure system architecture and engineering principles partial match
prevents

Secure architecture principles promote type-safe languages and memory-safety mechanisms that mitigate type confusion.

A.8.28 Secure coding partial match
prevents

Secure coding standards directly forbid unsafe type casts and require static-analysis checks for type confusion.

References