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CVE-2018-18500

CriticalPublished

A use-after-free vulnerability can occur while parsing an HTML5 stream in concert with custom HTML elements. This results in the stream parser object being...

Published: Feb 5, 2019
Updated: Aug 5, 2024
Assigning CNA: mozilla
Evidence observed: Aug 4, 2026

Primary CVSS

9.8/ 10Critical

nvd · CVSS 3.0

CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

EPSS probability estimate

11.6%

Moderate · next 30 days

Percentile: 95.9%
Model date: Sep 21, 2026

EPSS is a statistical estimate, not a certainty or a measure of impact. Combine it with CVSS, KEV status, exposure and your environment.

Summary

A use-after-free vulnerability can occur while parsing an HTML5 stream in concert with custom HTML elements. This results in the stream parser object being freed while still in use, leading to a potentially exploitable crash. This vulnerability affects Thunderbird < 60.5, Firefox ESR < 60.5, and Firefox < 65.

Sources

CVE-2018-18500PoC
PoC for CVE-2018-18500 - Firefox Use-After-Free

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