How severe is CVE-2021-28121?

CVE-2021-28121 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2021-28121 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (74th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-28121?

CVE-2021-28121 affects Virtual Robots.txt Project Virtual Robots.txt. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-28121?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.

When was CVE-2021-28121 published?

CVE-2021-28121 was published on 2021-08-12 and last updated on 2026-06-17.

CVE-2021-28121

CVE-2021-28121 is a critical-severity vulnerability in Virtual Robots.txt Project Virtual Robots.txt with a CVSS 3.x base score of 9.8. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low.

Key facts

Severity: Critical (CVSS 3.x base score 9.8)
CVSS v2: 7.5
EPSS exploit prediction: 2% (74th percentile)
Actively exploited: Not listed in CISA KEV
Affected product: Virtual Robots.txt Project Virtual Robots.txt
Published: 2021-08-12
Last modified: 2026-06-17

Description

Virtual Robots.txt before 1.10 does not block HTML tags in the robots.txt field.

Frequently asked questions

What is CVE-2021-28121?: Virtual Robots.txt before 1.10 does not block HTML tags in the robots.txt field.
How severe is CVE-2021-28121?: CVE-2021-28121 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2021-28121 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (74th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-28121?: CVE-2021-28121 affects Virtual Robots.txt Project Virtual Robots.txt. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-28121?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
When was CVE-2021-28121 published?: CVE-2021-28121 was published on 2021-08-12 and last updated on 2026-06-17.

References

https://wordpress.org/plugins/pc-robotstxt/#developers

Affected products (1)

cpe:2.3:a:virtual_robots.txt_project:virtual_robots.txt:*:*:*:*:*:wordpress:*:*