VulnerabilityModified

CVE-2021-39338

MEDIUM 4.8EPSS 0.95%

Does this matter?

Lower severity and a low EPSS score (0.95%). Track it; it rarely justifies an emergency change on its own.

Description

The MyBB Cross-Poster WordPress plugin is vulnerable to Stored Cross-Site Scripting due to insufficient input validation and sanitization via several parameters found in the ~/classes/MyBBXPSettings.php file which allowed attackers with administrative user access to inject arbitrary web scripts, in versions up to and including 1.0. This affects multi-site installations where unfiltered_html is disabled for administrators, and sites where unfiltered_html is disabled.

CVSS 3.1: 4.8 MEDIUMCVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:C/C:L/I:L/A:N
EPSS: 0.95% probability · 61th percentile
Public exploits: None in Exploit-DB
CISA KEV: Not listed
Weakness: CWE-79
Affected: mybb cross-poster project/mybb cross-poster
Source: security@wordfence.com

EPSS trend

EPSS 0.9% since 26 October 2026; no change recorded yet. Points are recorded when the score first appears and whenever it moves by a percentage point or more.

References

https://github.com/BigTiger2020/word-press/blob/main/MyBB%20Cross-Poster.mdExploit, Third Party Advisory
https://plugins.trac.wordpress.org/browser/mybb-cross-poster/trunk/classes/MyBBXPSettings.phpPatch, Third Party Advisory
https://www.wordfence.com/vulnerability-advisories/#CVE-2021-39338Third Party Advisory
https://github.com/BigTiger2020/word-press/blob/main/MyBB%20Cross-Poster.mdExploit, Third Party Advisory
https://plugins.trac.wordpress.org/browser/mybb-cross-poster/trunk/classes/MyBBXPSettings.phpPatch, Third Party Advisory
https://www.wordfence.com/vulnerability-advisories/#CVE-2021-39338Third Party Advisory

Source: NVD record, EPSS from FIRST.org, KEV from CISA, exploits from Exploit-DB. Refreshed daily. Download this record as JSON.