CVE-2026-45116Network attack vector

Stored XSS via profile field type confusion

Published Aug 18, 2026 · Updated Aug 18, 2026

Stored XSS in MyBB before 1.8.40 allows remote authenticated users to execute JavaScript in viewers' browsers via crafted profile fields. In UserDataHandler::verify_profile_fields(), checkbox and multiselect fields are only specially validated when profile_fields[fidX] arrives as an array, so a scalar profile_fields[fidX] value falls through generic text handling and is stored without verification; member.php and inc/functions_post.php then render that stored value directly. Exploitation requires an account that can submit profile field updates and a victim who views affected profile output, with browser-side script execution in the MyBB origin rather than server-side code execution.

CVSS severity8.7
High
EPSS probability0.30%
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 MyBB before 1.8.40 allows remote authenticated users to execute JavaScript in viewers' browsers via crafted profile fields. In UserDataHandler::verify_profile_fields(), checkbox and multiselect fields are only specially validated when profile_fields[fidX] arrives as an array, so a scalar profile_fields[fidX] value falls through generic text handling and is stored without verification; member.php and inc/functions_post.php then render that stored value directly. Exploitation requires an account that can submit profile field updates and a victim who views affected profile output, with browser-side script execution in the MyBB origin rather than server-side code execution.

The record

CVE
CVE-2026-45116
Published
Aug 18, 2026
Updated
Aug 18, 2026
Vendor
MyBB Group
Product
MyBB
Classifications
CWE-79, T1059.007
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Aug 18, 2026CVE publishedPublication date reported by the CVE source.
  2. Aug 18, 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=< 1.8.40

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

MyBB Group · MyBBversion=< 1.8.40

Published CVSS scores

8.7GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 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')
T1059.007Command and Scripting Interpreter: JavaScript

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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