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CVE-2026-39960

MantisBT is Vulnerable to Stored XSS through Custom Field Textarea Values

5.4 MediumFix available

Mantis Bug Tracker (MantisBT) is an open source issue tracker. Versions 2.28.1 and below contain flawed logic that causes improper escaping of a textarea custom field's contents in the Update Issue page, (bug_update_page.php) allowing an attacker to inject HTML and, if CSP settings permit, execute arbitrary JavaScript when the page is loaded. This facilitates session theft, leading to admin account takeover, full project data access. In order to exploit this issue, a textarea-type custom field must be configured for the project, the attack must be carried out by an authenticated user with bug report permission (low privilege). This can affect any user viewing the bug edit form, including administrators. The issue has been fixed in version 2.28.2. If users cannot immediately upgrade, they can work around the issue by using the default Content-Security Policy, which blocks script execution.

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
Low
Privileges needed
Low
User interaction
Required

What an attacker can affect

Confidentiality
Low
Integrity
Low
Availability
None

Exploit likelihood

0.23%Up 0.2 points since May 21, 2026
90%50%10%1%

What each source reports

CVE List Score used 5.4

MantisBT is Vulnerable to Stored XSS through Custom Field Textarea Values

Mantis Bug Tracker (MantisBT) is an open source issue tracker. Versions 2.28.1 and below contain flawed logic that causes improper escaping of a textarea custom field's contents in the Update Issue page, (bug_update_page.php) allowing an attacker to inject HTML and, if CSP settings permit, execute arbitrary JavaScript when the page is loaded. This facilitates session theft, leading to admin account takeover, full project data access. In order to exploit this issue, a textarea-type custom field must be configured for the project, the attack must be carried out by an authenticated user with bug report permission (low privilege). This can affect any user viewing the bug edit form, including administrators. The issue has been fixed in version 2.28.2. If users cannot immediately upgrade, they can work around the issue by using the default Content-Security Policy, which blocks script execution.

Record
CVE-2026-39960
CVSS 3.1
5.4 MediumCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
Weakness
CWE-79
Updated
2026-11-02
EUVDEUVD-2026-31192 5.4

Mantis Bug Tracker (MantisBT) is an open source issue tracker. Versions 2.28.1 and below contain flawed logic that causes improper escaping of a textarea custom field's contents in the Update Issue page, (bug_update_page.php) allowing an attacker to inject HTML and, if CSP settings permit, execute arbitrary JavaScript when the page is loaded. This facilitates session theft, leading to admin account takeover, full project data access. In order to exploit this issue, a textarea-type custom field must be configured for the project, the attack must be carried out by an authenticated user with bug report permission (low privilege). This can affect any user viewing the bug edit form, including administrators. The issue has been fixed in version 2.28.2. If users cannot immediately upgrade, they can work around the issue by using the default Content-Security Policy, which blocks script execution.

Record
EUVD-2026-31192
CVSS 3.1
5.4 MediumCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
Updated
2026-11-02
GitHub AdvisoriesGHSA-qj6w-v29q-4rgx 5.4

MantisBT is Vulnerable to Stored XSS in Custom Field Textarea Values

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.

Impact

Session theft leading to admin account takeover, full project data access.

  • Precondition: A textarea-type custom field must be configured for the project
  • Attacker: Authenticated user with bug report permission (low privilege)
  • Victim: Any user viewing the bug edit form, including administrators

Patches

  • 5fec0f448b7a7d7d539a6adb6dccceac4e4e4ab7

Workarounds

The default Content-Security Policy will block script execution.

References

Credits

Thanks to the following security researchers for independently discovering and responsibly reporting the issue, and providing a patch to fix it.

  • Thanks to Nozomu Sasaki (Paul) (@morimori-dev)
  • Tristan Madani (@TristanInSec) from Talence Security
Record
GHSA-qj6w-v29q-4rgx
CVSS 3.1
5.4 MediumCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
Weakness
CWE-79
Updated
2026-11-02
NVD 5.4

Mantis Bug Tracker (MantisBT) is an open source issue tracker. Versions 2.28.1 and below contain flawed logic that causes improper escaping of a textarea custom field's contents in the Update Issue page, (bug_update_page.php) allowing an attacker to inject HTML and, if CSP settings permit, execute arbitrary JavaScript when the page is loaded. This facilitates session theft, leading to admin account takeover, full project data access. In order to exploit this issue, a textarea-type custom field must be configured for the project, the attack must be carried out by an authenticated user with bug report permission (low privilege). This can affect any user viewing the bug edit form, including administrators. The issue has been fixed in version 2.28.2. If users cannot immediately upgrade, they can work around the issue by using the default Content-Security Policy, which blocks script execution.

Record
CVE-2026-39960
CVSS 3.1
5.4 MediumCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
Weakness
CWE-79
Updated
2026-11-02
OSV 5.4

MantisBT is Vulnerable to Stored XSS through Custom Field Textarea Values

Mantis Bug Tracker (MantisBT) is an open source issue tracker. Versions 2.28.1 and below contain flawed logic that causes improper escaping of a textarea custom field's contents in the Update Issue page, (bug_update_page.php) allowing an attacker to inject HTML and, if CSP settings permit, execute arbitrary JavaScript when the page is loaded. This facilitates session theft, leading to admin account takeover, full project data access. In order to exploit this issue, a textarea-type custom field must be configured for the project, the attack must be carried out by an authenticated user with bug report permission (low privilege). This can affect any user viewing the bug edit form, including administrators. The issue has been fixed in version 2.28.2. If users cannot immediately upgrade, they can work around the issue by using the default Content-Security Policy, which blocks script execution.

Record
CVE-2026-39960
CVSS 3.1
5.4 MediumCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
Weakness
CWE-79
Updated
2026-11-02
OSVGHSA-qj6w-v29q-4rgx 5.4

MantisBT is Vulnerable to Stored XSS in Custom Field Textarea Values

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.

Impact

Session theft leading to admin account takeover, full project data access.

  • Precondition: A textarea-type custom field must be configured for the project
  • Attacker: Authenticated user with bug report permission (low privilege)
  • Victim: Any user viewing the bug edit form, including administrators

Patches

  • 5fec0f448b7a7d7d539a6adb6dccceac4e4e4ab7

Workarounds

The default Content-Security Policy will block script execution.

References

Credits

Thanks to the following security researchers for independently discovering and responsibly reporting the issue, and providing a patch to fix it.

  • Thanks to Nozomu Sasaki (Paul) (@morimori-dev)
  • Tristan Madani (@TristanInSec) from Talence Security
Record
GHSA-qj6w-v29q-4rgx
CVSS 3.1
5.4 MediumCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
Weakness
CWE-79
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
mantisbt/mantisbt
Packagist
 through 2.28.1
2.28.2
mantisbt/mantisbt
Packagist
 before 2.28.2, plus listed versions
2.10.02.10.12.11.02.11.12.12.0
Show 45 moreShow less
2.12.12.12.22.13.02.13.12.13.22.14.02.15.02.15.12.16.02.16.12.17.02.17.12.17.22.18.02.18.12.19.02.19.12.20.02.20.12.21.02.21.12.21.22.21.32.22.02.22.12.22.22.23.02.23.12.24.02.24.12.24.22.24.32.24.42.24.52.25.02.25.12.25.22.25.32.25.42.25.52.25.62.25.72.25.82.26.02.26.1
2.28.2

History

History
RecordedChangedSources
first indexedCVE List, EUVD, GitHub Advisories, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2026-39960 is a medium vulnerability (CVSS 5.4) in Mantisbt, published May 11, 2026. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.23%, the 13th percentile. Fixed in mantisbt/mantisbt 2.28.2.

References

This page doesn't list everything

Left out here: 26 versions. The JSON record has them.

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