An issue was discovered in inc/class_feedgeneration.php in MyBB 1.8.17. On the forum RSS Syndication page, one can generate a URL such as http://localhost/syndication.php?fid=&type=atom1.0&limit=15. The thread titles (within title elements of the generated XML documents) aren't sanitized, leading to XSS.
Severity
CVSS 3.0
6.1 medium
CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
EPSS
2.3% chance of exploitation in the next 30 days; higher than 82% of CVEs (scores of 2026-10-31)