CVE intelligence and bounded remediation

CVE-2018-1000874 — Cebe Markdown security vulnerability

Medium CVSS 6.1

PHP cebe markdown parser version 1.2.0 and earlier contains a Cross Site Scripting (XSS) vulnerability in all distributed parsers allowing a malicious crafted script to be executed that can result in the lose of user data and sensitive user information. This attack can be exploited by crafting a three backtick wrapped payload with a character in front: L: "```<script>alert();</script>```". NOTE: This has been argued as a non-issue (see references) since it is not the parser's job to sanitize malicious code from a parsed document

Severity
Medium
CVSS
6.1 (3.1)
Published
2018-12-20
CISA KEV
Not currently listed
Ecosystem
software/application
Weaknesses
CWE-79

Affected products

  • cebe / markdown

Matched remediation archetype

Cross-site scripting and unsafe browser output

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Check exposure

  • Trace reflected, stored, and DOM-derived untrusted values into HTML, attributes, URLs, styles, scripts, and client-side template sinks.
  • Identify affected origins, authenticated user roles, sensitive browser capabilities, and where content is shared across tenants.
  • Review framework escaping, rich-text sanitization, legacy templates, and client-side rendering paths.

Remediate safely

  • Use context-aware framework output encoding and safe DOM APIs; keep untrusted data out of executable contexts.
  • Sanitize intentionally supported markup with a maintained allowlist policy and validate URLs and attributes separately.
  • Update affected rendering components and add tests for every output context using inert sentinel markup.

Authoritative sources

Complete CVE record and remediation plan

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