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TI-2021-16705 Aliases CVE-2021-39338GHSA-p7r5-mv7j-8m3r

MyBB Cross-Poster <= 1.0 Authenticated Stored Cross-Site Scripting

Priority LOW 27CWE-79Published · Updated

Key facts

Attack vector
Network
Privileges required
High
User interaction
None
Attack complexity
Low
Impact type
Cross-site scripting
Confidentiality · integrity · availability
Low · Low · None
Fix status
No fix listed

Attack profile from CVSS 3.1 · CNA. Fix status from CNA. Impact type from CWE-79.

Summary

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.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00946 61st percentileScored 2026-11-07
Public exploit Yes 1 exploit referenceTagged by NVD
Fix No fix listed No fixed version in the sources yet

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
None
Automatable
No
Technical impact
Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
MyBB Cross-PosterMyBB Cross-Poster1.0 – 1.0—No fix listedCNA
  • MyBB Cross-Poster VendorMyBB Cross-Poster Affected 1.0 – 1.0 Fixed in — No fix listed CNA

CPE configurations NVD · 1

CPEVersionsRoleVendor
cpe:2.3:a:mybb_cross-poster_project:mybb_cross-poster:*:*:*:*:*:wordpress:*:*up to 1.0VulnerableMybb Cross-poster Project
  • cpe:2.3:a:mybb_cross-poster_project:mybb_cross-poster:*:*:*:*:*:wordpress:*:* Versions up to 1.0 Vulnerable ·Mybb Cross-poster Project

Remediation

No fixed version listed by the sources yet.

Timeline

  1. 2026-10-02 Threatist record created from CVE-2021-39338
  2. 2026-10-03 Alias added: GHSA-p7r5-mv7j-8m3r

References

Exploit 1

Patch 1

Advisory 1

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences