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CVE-2026-45115

MyBB: Buddy/ignore list username XSS

HIGH
8.7
CVSS Score
Published: August 18, 2026 at 03:46 PM UTC
Updated: September 8, 2026 at 09:19 PM UTC
1 product affected across 1 vendorMybb

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Severity
HIGH8.7
Exploit prediction
EPSS 0.4%
SSVC
No known exploit

Description

MyBB is free and open source forum software. Prior to 1.8.40, the Buddy/Ignore component does not sanitize usernames correctly, allowing attackers to perform JavaScript code injection through a specially crafted username. The User CP Buddy/Ignore list and the Select Buddies list in Private Messages pass usernames through htmlspecialchars_uni(), which may leave single quotes unescaped. The payload is triggered when a victim chooses Yes in Please Confirm while removing the username in usercp.php, or selects the username through the onclick handler in the xmlhttp.php Select Buddies popup. The uniquely identifying implementation details include Private Messages Select Buddies list, and unescaped single quotes. This issue is fixed in version 1.8.40.

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

Mybb· Mybb
60%
v < 1.8.40
Affected range stops below 1.8.40, so it looks safe — our inference, not a vendor statement

Remediation

No guide yet

No remediation guidance has been written for this CVE yet, and no fixed version or vendor advisory is recorded against it.

References (3)

x_refsource_CONFIRM
Source: cverecord
https://github.com/mybb/mybb/security/advisories/GHSA-p766-qqxv-rfc2
x_refsource_MISC
Source: cverecord
https://github.com/mybb/mybb/releases/tag/mybb_1840
x_refsource_MISC
Source: cverecord
https://mybb.com/versions/1.8.40

SSVC — Action Prioritization

SSVCNo known exploitNot automatableTotal impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

8.7HIGHGitHub_M
Attack Vector
NETWORK
Complexity
LOW
Privileges
LOW
User Interaction
REQUIRED
Scope
CHANGED
Confidentiality
HIGH
Integrity
HIGH
Availability
NONE
Vector?

Quick Info

StatusDEFERRED
CWE
CWE-79

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