CVE-2019-17026Known exploitationPublic exploitNetwork attack vector

Memory corruption via incorrect JIT alias modeling

Published Mar 2, 2020 · Updated Oct 21, 2025

Type confusion in Mozilla Firefox before 72.0.1, Firefox ESR before 68.4.1, and Thunderbird before 68.4.1 allows remote attackers to corrupt memory. IonMonkey's StoreElementHole and FallibleStoreElement operations modeled array stores as side-effect-free, so a negative index could invoke a property setter without invalidating optimized assumptions. Exploitation requires JavaScript execution in a browser or browser-like context; Thunderbird mail reading disables scripting, and successful abuse permits memory read, write, or a crash.

CVSS severity8.8
High
EPSS probability46.31%
Next 30 days · Sep 16, 2026
Known exploitationReported
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Type confusion in Mozilla Firefox before 72.0.1, Firefox ESR before 68.4.1, and Thunderbird before 68.4.1 allows remote attackers to corrupt memory. IonMonkey's StoreElementHole and FallibleStoreElement operations modeled array stores as side-effect-free, so a negative index could invoke a property setter without invalidating optimized assumptions. Exploitation requires JavaScript execution in a browser or browser-like context; Thunderbird mail reading disables scripting, and successful abuse permits memory read, write, or a crash.

The record

CVE
CVE-2019-17026
Published
Mar 2, 2020
Updated
Oct 21, 2025
Vendor
Mozilla
Product
Firefox
Classifications
CWE-843, T1203
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 2, 2020CVE publishedPublication date reported by the CVE source.
  2. Oct 21, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=unspecified <72.0.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Mozilla · Firefoxversion=unspecified <72.0.1
Mozilla · Thunderbirdversion=unspecified <68.4.1
Mozilla · Firefox ESRversion=unspecified <68.4.1

Published CVSS scores

8.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationReported
Public exploitPublished

Weakness, pattern, technique

CWE-843Access of Resource Using Incompatible Type ('Type Confusion')
T1203Exploitation for Client Execution

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Reported exploitation

Technologies

Your stack

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Your stack

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