CVE-2019-17026

Exp

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.

Published: 2020-03-02 Last update: 2025-11-04 Assigner: [email protected] Source: [email protected]
NVD Status：Analyzed，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2019-17026 is rated Critical Active Threat (91.1/100): CVSS High severity, with high exploitation likelihood (EPSS 56.19%, 98th percentile). CISA KEV confirms active exploitation (added 2021-11-03) affecting Mozilla / Firefox and Thunderbird. a weakness (CWE-843) Unauthenticated remote administrative access may be possible. The CISA remediation deadline has passed—treat as an emergency patch priority.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

CISA KEV Record for CVE-2019-17026

Name: Mozilla Firefox And Thunderbird Type Confusion Vulnerability · CISA KEV detail

Exploit added: 2021-11-03

Action due: 2022-05-03

Required action: Apply updates per vendor instructions.

Public exploit references (Exploit-DB) for CVE-2019-17026

EDB-ID Source Kind Published Link
49864 exploit_db edb 2021-05-13 Exploit-DB ↗
— nvd_ref exploit_tag Exploit-DB ↗

Exploit prediction scoring system (EPSS) score for CVE-2019-17026

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-05-29 59.68% 56.19% -3.49%
2 2026-05-26 55.55% 59.68% +4.13%
3 2026-05-24 — 55.55% —

Full EPSS history (61 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2019-17026

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
8.8 3.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:R)
A real person has to do something—click, install, enable—otherwise it doesn’t land.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 2.8 5.9 [email protected]
8.8 3.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:R)
A real person has to do something—click, install, enable—otherwise it doesn’t land.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 2.8 5.9 134c704f-9b21-4f2e-91b3-4a467353bcc0
6.8 2.0 MEDIUM
AV:N/AC:M/Au:N/C:P/I:P/A:P Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:M)
Exploitation needs some favorable conditions, but not exceptional ones.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:P)
Partial confidentiality impact.
Integrity impact (I:P)
Partial integrity impact.
Availability impact (A:P)
Partial availability impact.
 8.6 6.4 [email protected]

Weakness enumeration for CVE-2019-17026

OS Trackers for CVE-2019-17026

vendor priority summary link
alpine — CVE-2019-17026: 3 source package rows (firefox, firefox-esr, librewolf); 21 state rows across 7 repos (3.17-community, 3.18-community, 3.19-community, 3.20-community, 3.21-community, 3.22-community, edge-community); fixed 19, open 2. https://security.alpinelinux.org/vuln/CVE-2019-17026
debian not yet assigned CVE-2019-17026 not yet assigned priority: Debian including 3 source packages (firefox, firefox-esr, thunderbird), 11 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 11. https://security-tracker.debian.org/tracker/CVE-2019-17026
gentoo normal CVE-2019-17026: 1 GLSA(s) (202003-02), 2 atom(s) (www-client/firefox, www-client/firefox-bin); latest impact normal. https://bugs.gentoo.org/buglist.cgi?quicksearch=CVE-2019-17026
redhat critical — https://access.redhat.com/security/cve/CVE-2019-17026
ubuntu medium CVE-2019-17026 medium priority: Ubuntu including 5 source packages (firefox, mozjs38, mozjs52, mozjs60, thunderbird), 75 status rows across 15 suites (bionic, disco, eoan, focal, groovy, hirsute, impish, jammy, kinetic, lunar, mantic, noble, trusty, upstream, xenial): DNE 36, released 27, ignored 12. https://ubuntu.com/security/CVE-2019-17026

Affected software / configurations for CVE-2019-17026

Vendor Product Version Raw CPE
mozilla firefox < 68.4.1 cpe:2.3:a:mozilla:firefox:*:*:*:*:esr:*:*:*
mozilla firefox < 72.0.1 cpe:2.3:a:mozilla:firefox:*:*:*:*:-:*:*:*
mozilla thunderbird < 68.4.1 cpe:2.3:a:mozilla:thunderbird:*:*:*:*:*:*:*:*
canonical ubuntu_linux 16.04 cpe:2.3:o:canonical:ubuntu_linux:16.04:*:*:*:esm:*:*:*

References for CVE-2019-17026

cvelogic Threat Intelligence