CVE-2026-39960Network attack vector

Session theft via unescaped custom-field textarea values

Published May 20, 2026 · Updated May 20, 2026

Stored XSS in MantisBT 2.28.1 and earlier allows remote authenticated users to inject HTML into issue update forms and steal viewer sessions. In core/cfdefs/cfdef_standard.php, cfdef_input_textarea() writes $p_custom_field_value directly between textarea tags without string_textarea() escaping. Exploitation requires a configured textarea custom field, bug-report permission, a victim opening the edit form, and CSP settings that allow script execution; stolen administrator sessions expose full project data.

CVSS severity5.4
Medium
EPSS probability0.23%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Stored XSS in MantisBT 2.28.1 and earlier allows remote authenticated users to inject HTML into issue update forms and steal viewer sessions. In core/cfdefs/cfdef_standard.php, cfdef_input_textarea() writes $p_custom_field_value directly between textarea tags without string_textarea() escaping. Exploitation requires a configured textarea custom field, bug-report permission, a victim opening the edit form, and CSP settings that allow script execution; stolen administrator sessions expose full project data.

The record

CVE
CVE-2026-39960
Published
May 20, 2026
Updated
May 20, 2026
Vendor
MantisBT
Product
MantisBT
Classifications
CWE-79, T1539
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. May 20, 2026CVE publishedPublication date reported by the CVE source.
  2. May 20, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 2.28.2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

MantisBT · MantisBTversion=< 2.28.2

Published CVSS scores

5.4GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1539Steal Web Session Cookie

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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