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CVE Record

CVE-2018-18500: A use-after-free vulnerability can occur while parsing an HTML5 stream in concert with custom HTML elements.

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.

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

This is a memory-safety bug in older Firefox, Firefox ESR, and Thunderbird releases. A specially crafted HTML5 stream involving custom HTML elements could make the parser use an object after it was freed, causing a potentially exploitable crash. The business issue is outdated browser or mail-client software, not a server-side exposure.

Executive priority

Prioritize remediation if legacy Firefox or Thunderbird remains in managed fleets, kiosks, VDI images, or long-lived Linux systems. No active exploitation evidence is provided, but the affected software is client-facing and the bug is described as potentially exploitable, so unresolved exposure should not be accepted indefinitely.

Technical view

CVE-2018-18500 is a use-after-free in Mozilla's HTML5 stream parser when handling custom HTML elements. The CVE states the stream parser object may be freed while still in use, leading to a potentially exploitable crash. Affected versions are Thunderbird before 60.5, Firefox ESR before 60.5, and Firefox before 65.

Likely exposure

Exposure is most likely on endpoints or managed systems still running Firefox before 65, Firefox ESR before 60.5, or Thunderbird before 60.5. Distribution-packaged Mozilla builds referenced by Red Hat, Ubuntu, Debian, and Gentoo advisories should be checked against vendor-fixed package versions.

Exploitation context

The provided sources do not show CISA KEV listing or confirmed active exploitation. The CVE description supports potential exploitability through parser memory corruption, but does not provide exploitation-in-the-wild evidence. Treat this as a legacy client-side risk requiring remediation where old Mozilla builds remain installed.

Researcher notes

Focus validation on version and package provenance. The source bundle does not include CVSS, CWE, exploit indicators, or a detailed root-cause patch reference. Avoid assuming affected products beyond Firefox, Firefox ESR, Thunderbird, and vendor-packaged equivalents named in advisories.

Mitigation direction

  • Upgrade Firefox to version 65 or later.
  • Upgrade Firefox ESR to version 60.5 or later.
  • Upgrade Thunderbird to version 60.5 or later.
  • Apply fixed OS vendor packages from Red Hat, Ubuntu, Debian, or Gentoo advisories.
  • Check Mozilla and distribution advisories for environment-specific package names.

Validation and detection

  • Inventory installed Firefox, Firefox ESR, and Thunderbird versions across endpoints.
  • Confirm no Firefox builds are older than version 65.
  • Confirm no Firefox ESR or Thunderbird builds are older than version 60.5.
  • Review Linux package status against the referenced distribution advisories.
  • Check vulnerability scanners for CVE-2018-18500 detections after patching.
Prepared
Confidence
medium
Sources
10

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

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Vulnerability profileCVE Program record
Severity
Unknown
CVSS
Not scored
Known Exploited
No
Published
Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

0CVSS vectors
0Timeline events
0ADP providers
16Source links

CVSS and timeline data

No CVSS vectors or timeline events were available in the normalized CVE source material.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
n/an/an/aListed
Weakness

CWE details

No CWE listed

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