XSS was discovered in SquirrelMail through 1.4.22 and 1.5.x through 1.5.2. Due to improper handling of RCDATA and RAWTEXT type elements, the built-in sanitization mechanism can be bypassed. Malicious script content from HTML e-mail can be executed within the application context via crafted use of (for example) a NOEMBED, NOFRAMES, NOSCRIPT, or TEXTAREA element.
https://www.syss.de/fileadmin/dokumente/Publikationen/Advisories/SYSS-2019-016.txt
https://seclists.org/bugtraq/2019/Jul/50
https://seclists.org/bugtraq/2019/Jul/0
https://lists.debian.org/debian-lts-announce/2019/08/msg00000.html
http://packetstormsecurity.com/files/153495/SquirrelMail-1.4.22-Cross-Site-Scripting.html