What is CVE-2021-33557?

CVE-2021-33557 is a medium-severity vulnerability in Mantisbt, classified under Cross-site Scripting. CVSS score: 6.1/10. Published 2021-06-17.

How severe is CVE-2021-33557?

Medium severity. CVSS v3 base score is 6.1 out of 10.

Is CVE-2021-33557 known to be exploited?

2 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.

XSS in Mantisbt

CVE-2021-33557

An XSS issue was discovered in manage_custom_field_edit_page.php in MantisBT before 2.25.2. Unescaped output of the return parameter allows an attacker to inject code into a hidden input field.

Vulnerability class: XSS (Cross-Site Scripting)

Published 2021-06-17 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 6.1 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N.

EPSS exploit prediction

EPSS: 0.018 (77.9th percentile), scored 2026-09-28.

Low probability of exploitation in the next 30 days, but still tracked. 78th percentile — 77.9% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.018 · newest: 0.018 · change: 0.000

Affected products

Mantisbt

Weakness classification (CWE)

CWE-79 — Cross-site Scripting

Public proof-of-concept exploits

References

mantisbt.org/bugs/view.php (Exploit, Vendor Advisory)
mantisbt.org/blog/archives/mantisbt/699 (Release Notes, Vendor Advisory)

Frequently asked questions

What is CVE-2021-33557?: CVE-2021-33557 is a medium-severity vulnerability in Mantisbt, classified under Cross-site Scripting. CVSS score: 6.1/10. Published 2021-06-17.
How severe is CVE-2021-33557?: Medium severity. CVSS v3 base score is 6.1 out of 10.
Is CVE-2021-33557 known to be exploited?: 2 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.