CVE-2026-39960: Mantisbt/mantisbt Cross-Site Scripting Vulnerability

MODERATE
Advisory Identifier: GHSA-qj6w-v29q-4rgx
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CVSS 5.4
CWE-79
Published
Advisory Summary

CVE-2026-39960 is a MODERATE (CVSS 5.4) cross-site scripting vulnerability (CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')) affecting Mantisbt/mantisbt libraries in the Packagist ecosystem. The issue involves mantisbt is vulnerable to stored xss in custom field textarea values. Remediation is available by upgrading affected packages to version 2.28.2.

CVE-2026-39960 at a Glance

CVE Identifier CVE-2026-39960
GHSA Identifier GHSA-qj6w-v29q-4rgx
Severity MODERATE
CVSS v3.1 Base Score 5.4
CWE Classification CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
Affected Product Mantisbt/mantisbt
Package Ecosystem Packagist
Published Date
Last Updated

Security Impact

CVSS: 5.4

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required Low (PR:L)
User Interaction Required (UI:R)
Scope Changed (S:C)
Confidentiality Low (C:L)
Integrity Low (I:L)
Availability None (A:N)

How to Fix CVE-2026-39960

To remediate this vulnerability, upgrade all affected Mantisbt/mantisbt dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

mantisbt/mantisbt fixed: 2.28.2 
Upgrade mantisbt/mantisbt to 2.28.2
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

inspect dependencies for mantisbt/mantisbt

How to Check if You Are Affected

To determine whether your application is affected by CVE-2026-39960, inspect your project dependencies for Mantisbt/mantisbt:

inspect dependencies for mantisbt/mantisbt

Analyze the terminal output to locate any version of Mantisbt/mantisbt in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 2.28.2), your application is affected.

Note: Verify declared build manifests and deployed runtime container environments.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting'), where the product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users. In Mantisbt/mantisbt, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

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 - https://mantisbt.org/bugs/view.php?id=37003 - This is related to [CVE-2024-34081](https://github.com/advisories/GHSA-wgx7-jp56-65mq). ### 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

CVE-2026-39960 Affected Mantisbt/mantisbt Versions

1 component(s)
Fixed Versions:
2.28.2
Product / Package Ecosystem Affected Versions Fixed Version
mantisbt/mantisbt
 Packagist
< 2.28.2
2.28.2

References

GitHub Advisory / Wiki ADVISORY
https://github.com/mantisbt/mantisbt/security/advisories/GHSA-qj6w-v29q-4rgx
NVD — CVE-2026-39960 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-39960
Security Fix Commit FIX COMMIT
https://github.com/mantisbt/mantisbt/commit/5fec0f448b7a7d7d539a6adb6dccceac4e4e4ab7
Mantisbt/mantisbt Source Repository REPOSITORY
https://github.com/mantisbt/mantisbt
mantisbt.org/bugs/view.php WEB
https://mantisbt.org/bugs/view.php?id=37003

Frequently Asked Questions

What is CVE-2026-39960?
CVE-2026-39960 is a security vulnerability in Mantisbt/mantisbt involving MantisBT is Vulnerable to Stored XSS in Custom Field Textarea Values under CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting').
Which Mantisbt/mantisbt versions are affected?
Affected versions include releases prior to 2.28.2 across affected packages: mantisbt/mantisbt.
What version fixes CVE-2026-39960?
Upgrading to 2.28.2 (or the latest patched release for your respective branch) resolves the vulnerability.
Is mantisbt/mantisbt affected?
Yes, mantisbt/mantisbt is affected in releases prior to 2.28.2. Upgrade your dependency to 2.28.2 or later.
What is the CVSS score of CVE-2026-39960?
CVE-2026-39960 has a CVSS v3.1 base score of 5.4 (MODERATE) with vector string CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N.
What CWE is associated with CVE-2026-39960?
CVE-2026-39960 is classified under CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') (The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.).
How can I check Packagist dependencies for CVE-2026-39960?
Run the dependency tree command: 'inspect dependencies for mantisbt/mantisbt'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-qj6w-v29q-4rgx",
  "modified" : "2026-06-08T20:14:49Z",
  "published" : "2026-05-11T19:34:32Z",
  "aliases" : [ "CVE-2026-39960" ],
  "summary" : "MantisBT is Vulnerable to Stored XSS in Custom Field Textarea Values",
  "details" : "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.\n\n### Impact\nSession theft leading to admin account takeover, full project data access.\n\n- Precondition: A textarea-type custom field must be configured for the project\n- Attacker: Authenticated user with bug report permission (low privilege)\n- Victim: Any user viewing the bug edit form, including administrators\n\n### Patches\n- 5fec0f448b7a7d7d539a6adb6dccceac4e4e4ab7\n\n### Workarounds\nThe default Content-Security Policy will block script execution.\n\n### References\n- https://mantisbt.org/bugs/view.php?id=37003\n- This is related to [CVE-2024-34081](https://github.com/advisories/GHSA-wgx7-jp56-65mq).\n\n### Credits\nThanks to the following security researchers for independently discovering and responsibly reporting the issue, and providing a patch to fix it.\n- Thanks to Nozomu Sasaki (Paul) (@morimori-dev)\n- Tristan Madani (@TristanInSec) from Talence Security",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Packagist",
      "name" : "mantisbt/mantisbt"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "2.28.2"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 2.28.1"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/mantisbt/mantisbt/security/advisories/GHSA-qj6w-v29q-4rgx"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-39960"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mantisbt/mantisbt/commit/5fec0f448b7a7d7d539a6adb6dccceac4e4e4ab7"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/mantisbt/mantisbt"
  }, {
    "type" : "WEB",
    "url" : "https://mantisbt.org/bugs/view.php?id=37003"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-79" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-05-11T19:34:32Z",
    "nvd_published_at" : "2026-05-20T22:16:36Z"
  }
}