** DISPUTED ** 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.

References

• https://nvd.nist.gov/vuln/detail/CVE-2018-1000874
• cebe/markdown#166
• cebe/markdown#166 (comment)