CVE-2021-39338MyBB Cross-Poster <= 1.0 Authenticated Stored Cross-Site Scripting
- 5.5MediumCVSS base score
- 0.95%Exploitation in 30 daysEPSS · top 38% of all CVEs
- NoKnown exploitednot in CISA's KEV catalog
- NonePublic exploitsnone known yet
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.
Timeline
ID reserved
By Wordfence
- 56 days later
· 56 days later
Published
- 3 years later
· 3 years later
Record updated
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
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| WordfenceCNA (assigner) | 3.1 | Medium5.5 | CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:C/C:L/I:L/A:N |
| NVDNVD · Modified | 3.1 | Medium4.8 | CVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:C/C:L/I:L/A:N |
- EPSS (exploitation in 30 days)
- 0.95% · top 38% of all CVEs (13 Nov 2026)
- CISA SSVC
- Exploitation: none · Automatable: no · Technical impact: partial
The list uses the assigner's score when there is one, then CISA's, then NVD's: Medium 5.5.
Affected products
MyBB Cross-Poster · MyBB Cross-Poster
- affected 1.0 – ≤ 1.0
What to do
Solution: Uninstall plugin from WordPress site.
References
References3
- https://www.wordfence.com/vulnerability-advisories/#CVE-2021-39338 (opens in a new tab)x_refsource_MISCx_transferred
- https://github.com/BigTiger2020/word-press/blob/main/MyBB%20Cross-Poster.md (opens in a new tab)x_refsource_MISCx_transferred
- https://plugins.trac.wordpress.org/browser/mybb-cross-poster/trunk/classes/MyBBXPSettings.php (opens in a new tab)x_refsource_MISCx_transferred
Sources
The same CVE in the primary databases and aggregators, to check against.
- CVE.org record (opens in a new tab)
- CVE List JSON (GitHub) (opens in a new tab)
- NVD (opens in a new tab)
- FIRST EPSS (opens in a new tab)
- EUVD EUVD-2021-25699 (opens in a new tab)
- OSV.dev (opens in a new tab)
- GitHub Advisories (opens in a new tab)
- CIRCL Vulnerability-Lookup (opens in a new tab)
Badge for a README or a ticket
[](https://cveledger.app/cve/CVE-2021-39338)Record last updated .