How severe is CVE-2021-27279?

CVE-2021-27279 has a CVSS 3.x base score of 5.4, rated medium severity. It is exploitable over network with low attack complexity, requires low privileges and user interaction. Impact on confidentiality is low, integrity low, and availability none.

Is CVE-2021-27279 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (57th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-27279?

CVE-2021-27279 affects Mybb. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-27279?

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

When was CVE-2021-27279 published?

CVE-2021-27279 was published on 2021-02-22 and last updated on 2026-06-17.

CVE-2021-27279

CVE-2021-27279 is a medium-severity vulnerability in Mybb with a CVSS 3.x base score of 5.4. 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 5.4)
CVSS v2: 3.5
EPSS exploit prediction: 1% (57th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-79
Affected product: Mybb
Published: 2021-02-22
Last modified: 2026-06-17

Description

MyBB before 1.8.25 allows stored XSS via nested [email] tags with MyCode (aka BBCode).

Frequently asked questions

What is CVE-2021-27279?: MyBB before 1.8.25 allows stored XSS via nested [email] tags with MyCode (aka BBCode).
How severe is CVE-2021-27279?: CVE-2021-27279 has a CVSS 3.x base score of 5.4, rated medium severity. It is exploitable over network with low attack complexity, requires low privileges and user interaction. Impact on confidentiality is low, integrity low, and availability none.
Is CVE-2021-27279 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (57th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-27279?: CVE-2021-27279 affects Mybb. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-27279?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2021-27279 published?: CVE-2021-27279 was published on 2021-02-22 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:mybb:mybb:*:*:*:*:*:*:*:*

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