CVE-2026-39960: MantisBT is Vulnerable to Stored XSS in Custom Field Textarea Values

May 11, 2026 (updated June 8, 2026)

Improper escaping of a textarea custom field’s contents in the Update Issue page (bug_update_page.php) allows an attacker to inject HTML and, if CSP settings permit, execute arbitrary JavaScript when the page is loaded.

References

github.com/advisories/GHSA-qj6w-v29q-4rgx
github.com/mantisbt/mantisbt/commit/5fec0f448b7a7d7d539a6adb6dccceac4e4e4ab7
github.com/mantisbt/mantisbt/security/advisories/GHSA-qj6w-v29q-4rgx
mantisbt.org/bugs/view.php?id=37003
nvd.nist.gov/vuln/detail/CVE-2026-39960

Code Behaviors & Features

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