CVE-2026-40597
MantisBT has a Content Security Policy bypass via attachments
Description
Given any pre-existing XSS / HTML injection vulnerability, an attacker can bypass the Content Security Policy's _script-src_ directive by uploading a crafted attachment to any issue that, when accessed via the _file_download.php_ link, will be downloaded with a valid JavaScript MIME type resulting in script execution. The uploaded payload must be sniffed as a valid JavaScript MIME type by PHP finfo (see file_create_finfo() API function). Non-JavaScript MIME types will not get imported in a `<script>` tag by the browser, due to response header X-Content-Type-Options being set to _nosniff_, which requires all imported JavaScript files to be a valid JavaScript MIME type. ### Impact Cross-site scripting ### Patches - 9e3bee2e7b909f4e3596985892b8bc8bee9e0bfe ### Workarounds None ### Credits Thanks to siunam (Tang Cheuk Hei) for discovering and responsibly reporting the issue.
How to fix CVE-2026-40597
To remediate CVE-2026-40597, upgrade the affected package to a fixed version below.
- —upgrade to 2.28.2 or later
Is CVE-2026-40597 being exploited?
Low — EPSS is 0.1%, meaning exploitation activity has not been observed at scale.
Affected packages (1)
- from 0, < 2.28.2
CVSS scores
| Source | Version | Severity | Vector |
|---|---|---|---|
| osv | CVSS 4.0 | — | CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:H/VI:H/VA:L/SC:N/SI:N/SA:N |