CriticalPublic exploit

Use-After-Free in HTML5 Stream Parser (Firefox/Thunderbird)

IdentifiersCVE-2018-18500CWE-416· Use After Free

CVE-2018-18500 is a use-after-free vulnerability in Mozilla's HTML5 stream parser, triggered when parsing HTML5 streams in conjunction with custom HTML elements. The vulnerability arises when the stream parser object is freed while it is still in use, which can lead to a potentially exploitable crash. This issue affects Thunderbird versions prior to 60.5, Firefox ESR versions prior to 60.5, and Firefox versions prior to 65.

For your environment

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ANALYST BRIEF

Impact, mitigation & remediation

What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.

Impact

What an attacker gets, and what they’ve been doing with it.

Successful exploitation of this vulnerability could allow an attacker to execute arbitrary code or cause a denial of service (crash) by enticing a user to visit a specially crafted web page. The use-after-free condition may be leveraged for remote code execution in the context of the affected application.

Mitigation

If you can’t patch tonight, do this now.

As a temporary mitigation, users can disable JavaScript or avoid visiting untrusted websites until the affected software is updated. Employing security features such as sandboxing and running the browser with least privilege can also reduce risk.

Remediation

Patch, then assume compromise.

Upgrade to Thunderbird 60.5 or later, Firefox ESR 60.5 or later, or Firefox 65 or later, where the vulnerability has been patched by Mozilla.

PUBLIC EXPLOITS

Exploits

1 valid exploit after Mallory filtered fakes, detection scripts, and README-only repos.

VALID 1 / 1 TOTALView more in app

CVE-2018-18500MaturityPoCVerified exploit

This repository is a proof-of-concept (PoC) exploit for CVE-2018-18500, a use-after-free vulnerability in Mozilla Firefox. The repository contains three files: a README with a brief description and reference, 'customelements_poc.html' (the main exploit file), and 'delay_http_server.py' (a simple Python HTTP server). The exploit works by serving the HTML file via the local HTTP server, which the user then opens in a vulnerable version of Firefox. The HTML/JavaScript code manipulates FormData, FileReader, and custom elements to trigger a use-after-free condition, using a delayed XML response to help with timing. The PoC demonstrates memory corruption but does not include a shell or code execution payload. The endpoints involved are 'http://127.0.0.1/customelements_poc.html' (the exploit) and 'http://127.0.0.1/delay.xml' (used for timing). The attack vector is browser-based, requiring user interaction (opening the exploit HTML in Firefox).

sophoslabsDisclosed Apr 18, 2019pythonhtmlbrowser

EXPOSURE SURFACE

Affected products & vendors

Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.

VendorProductType

CanonicalUbuntu Linuxoperating_system

DebianDebian Linuxoperating_system

MozillaFirefoxapplication

MozillaFirefox Esrapplication

MozillaThunderbirdapplication

Red HatEnterprise Linux Desktopoperating_system

Red HatEnterprise Linux Serveroperating_system

Red HatEnterprise Linux Server Ausoperating_system

Red HatEnterprise Linux Server Eusoperating_system

Red HatEnterprise Linux Server Tusoperating_system

Red HatEnterprise Linux Workstationoperating_system

Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.

ACTIVITY FEED

Recent activity

1 sources tracked across advisories and community write-ups. News coverage will land here when it surfaces.

1 SOURCESView more in app

No news coverage yet. Advisories and community discussion only.

What this page doesn’t show

The version that knows your environment.

This page is what’s public. Mallory adds the parts that aren’t: which of your assets are affected, which adversaries are exploiting it right now, which detections to deploy, and what to do tonight.

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Exposure mapping

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Threat actor evidence

Every observed campaign linking this CVE to a named adversary.

Associated malware

Malware families riding this exploit, with evidence and IOCs.

Detection signatures

YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.

Vendor-by-vendor mapping

Cross-references every affected SKU, including bundled OEM variants.

Social activity