CVE-2026-40596: Mantisbt/mantisbt Cross-Site Scripting Vulnerability

HIGH
Advisory Identifier: GHSA-j3v9-553h-x28j
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CWE-79
Published
Advisory Summary

CVE-2026-40596 is a HIGH 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 xss leading to account takeover via updating a user's font family preference. Remediation is available by upgrading affected packages to version 2.28.2.

CVE-2026-40596 at a Glance

CVE Identifier CVE-2026-40596
GHSA Identifier GHSA-j3v9-553h-x28j
Severity HIGH
CVSS v3.1 Base Score N/A
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

How to Fix CVE-2026-40596

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-2026-40596, 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

Any authenticated user can inject arbitrary HTML via updating their account's font family. ### Impact Cross-site scripting. The injected payload will be reflected in every MantisBT page. Leveraging another vulnerability (CSP bypass, see [GHSA-9c3j-xm6v-j7j3](https://github.com/mantisbt/mantisbt/security/advisories/GHSA-9c3j-xm6v-j7j3)), the attacker could achieve account takeover. ### Patches - 9e8409cdd979eba86ef532756fc47c1d8112d22d ### Workarounds None ### Credits Thanks to siunam (Tang Cheuk Hei) for discovering and responsibly reporting the issue.

CVE-2026-40596 Affected Mantisbt/mantisbt Versions

1 component(s)
Fixed Versions:
2.28.2
Product / Package Ecosystem Affected Versions Fixed Version
mantisbt/mantisbt
 Packagist
≥ 2.11.0
< 2.28.2
2.28.2

References

GitHub Advisory / Wiki ADVISORY
https://github.com/mantisbt/mantisbt/security/advisories/GHSA-9c3j-xm6v-j7j3
GitHub Advisory / Wiki ADVISORY
https://github.com/mantisbt/mantisbt/security/advisories/GHSA-j3v9-553h-x28j
NVD — CVE-2026-40596 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-40596
Security Fix Commit FIX COMMIT
https://github.com/mantisbt/mantisbt/commit/9e8409cdd979eba86ef532756fc47c1d8112d22d
Mantisbt/mantisbt Source Repository REPOSITORY
https://github.com/mantisbt/mantisbt
mantisbt.org/bugs/view.php WEB
https://mantisbt.org/bugs/view.php?id=37011
mantisbt.org/bugs/view.php WEB
https://mantisbt.org/bugs/view.php?id=37016

Frequently Asked Questions

What is CVE-2026-40596?
CVE-2026-40596 is a security vulnerability in Mantisbt/mantisbt involving MantisBT is Vulnerable to XSS leading to account takeover via updating a user's font family preference 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-2026-40596?
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 CWE is associated with CVE-2026-40596?
CVE-2026-40596 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-2026-40596?
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-j3v9-553h-x28j",
  "modified" : "2026-06-08T23:20:17Z",
  "published" : "2026-05-11T19:34:38Z",
  "aliases" : [ "CVE-2026-40596" ],
  "summary" : "MantisBT is Vulnerable to XSS leading to account takeover via updating a user's font family preference",
  "details" : "Any authenticated user can inject arbitrary HTML via updating their account's font family.\n\n### Impact\nCross-site scripting.\nThe injected payload will be reflected in every MantisBT page.\n\nLeveraging another vulnerability (CSP bypass, see [GHSA-9c3j-xm6v-j7j3](https://github.com/mantisbt/mantisbt/security/advisories/GHSA-9c3j-xm6v-j7j3)), the attacker could achieve account takeover.\n\n### Patches\n- 9e8409cdd979eba86ef532756fc47c1d8112d22d\n\n### Workarounds\nNone\n\n### Credits\nThanks to siunam (Tang Cheuk Hei) for discovering and responsibly reporting the issue.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:P/VC:H/VI:L/VA:L/SC:H/SI:H/SA:L"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Packagist",
      "name" : "mantisbt/mantisbt"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "2.11.0"
      }, {
        "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-9c3j-xm6v-j7j3"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mantisbt/mantisbt/security/advisories/GHSA-j3v9-553h-x28j"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-40596"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mantisbt/mantisbt/commit/9e8409cdd979eba86ef532756fc47c1d8112d22d"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/mantisbt/mantisbt"
  }, {
    "type" : "WEB",
    "url" : "https://mantisbt.org/bugs/view.php?id=37011"
  }, {
    "type" : "WEB",
    "url" : "https://mantisbt.org/bugs/view.php?id=37016"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-79" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-05-11T19:34:38Z",
    "nvd_published_at" : "2026-05-22T20:16:34Z"
  }
}