CVE-2026-45115Network attack vector

Stored XSS via unescaped username quotes

Published Aug 18, 2026 · Updated Aug 18, 2026

Stored XSS in the Buddy/Ignore component in MyBB before 1.8.40 allows remote authenticated users to execute JavaScript via a crafted username. The xmlhttp_buddyselect_online and xmlhttp_buddyselect_offline templates pass usernames through htmlspecialchars_uni() and then place them inside single-quoted onclick arguments, so a username containing a quote can break out of the handler and inject script. Reachability requires an attacker who can set a username and a victim who opens the affected buddy-management or Select Buddies interface, where the code runs in the victim's forum session.

CVSS severity8.7
High
EPSS probability0.29%
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 the Buddy/Ignore component in MyBB before 1.8.40 allows remote authenticated users to execute JavaScript via a crafted username. The xmlhttp_buddyselect_online and xmlhttp_buddyselect_offline templates pass usernames through htmlspecialchars_uni() and then place them inside single-quoted onclick arguments, so a username containing a quote can break out of the handler and inject script. Reachability requires an attacker who can set a username and a victim who opens the affected buddy-management or Select Buddies interface, where the code runs in the victim's forum session.

The record

CVE
CVE-2026-45115
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_MCVSS: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 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')
T1059.007JavaScript

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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