How severe is CVE-2021-39338?

CVE-2021-39338 has a CVSS 3.x base score of 5.5, rated medium severity. It is exploitable over network with low attack complexity, requires high privileges and no user interaction. Impact on confidentiality is low, integrity low, and availability none.

Is CVE-2021-39338 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (56th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-39338?

CVE-2021-39338 affects Mybb Cross-poster Project Mybb Cross-poster. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-39338?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

When was CVE-2021-39338 published?

CVE-2021-39338 was published on 2021-10-15 and last updated on 2026-06-17.

CVE-2021-39338

CVE-2021-39338 is a medium-severity vulnerability in Mybb Cross-poster Project Mybb Cross-poster with a CVSS 3.x base score of 5.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-79.

Key facts

Severity: Medium (CVSS 3.x base score 5.5)
CVSS v2: 2.1
EPSS exploit prediction: 1% (56th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-79
Affected product: Mybb Cross-poster Project Mybb Cross-poster
Published: 2021-10-15
Last modified: 2026-06-17

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.

Frequently asked questions

What is CVE-2021-39338?: 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.
How severe is CVE-2021-39338?: CVE-2021-39338 has a CVSS 3.x base score of 5.5, rated medium severity. It is exploitable over network with low attack complexity, requires high privileges and no user interaction. Impact on confidentiality is low, integrity low, and availability none.
Is CVE-2021-39338 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (56th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-39338?: CVE-2021-39338 affects Mybb Cross-poster Project Mybb Cross-poster. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-39338?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2021-39338 published?: CVE-2021-39338 was published on 2021-10-15 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:mybb_cross-poster_project:mybb_cross-poster:*:*:*:*:*:wordpress:*:*

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