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CVE-2026-45115

MyBB: Buddy/ignore list username XSS

High8.7EPSS 0.42%
Published
Updated
Reserved
Assigned by
GitHub_M

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.

Timeline

  1. ID reserved

    By GitHub_M

  2. · 3 months later

    Published

Changes after publication (a new score, a public exploit, EPSS crossing 1, 10 or 50 %, leaving KEV) are kept since November 2026; earlier ones are not known.

Scores

CVSS scores of CVE-2026-45115, by who scored it
Scored byCVSSScoreVector
GitHub_MCNA (assigner)3.1High8.7CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:N
NVDNVD · Deferred3.1High8.7CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:N
EPSS (exploitation in 30 days)
0.42% · top 64% of all CVEs (7 Nov 2026)
CISA SSVC
Exploitation: none · Automatable: no · Technical impact: total
Loading the EPSS history…

The list uses the assigner's score when there is one, then CISA's, then NVD's: High 8.7.

Weakness

Affected products

References (3)

Sources

The same CVE in the primary databases and aggregators, to check against.

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Record last updated .