CVE-2021-28121Public exploitNetwork attack vector

Admin-level stored XSS via unsanitized robots.txt content

Published Aug 12, 2021 · Updated Aug 3, 2024

Stored cross-site scripting in Virtual Robots.txt before 1.10 allows remote authenticated users to inject scripts through the robots.txt field. The settings handler saves the User Agents and Directives field without sanitizing HTML and echoes the stored value into the plugin settings page. Administrator access is required, and a later settings-page view executes the injected script in the viewer's browser under the site's origin.

CVSS severity5.5
Medium
EPSS probability1.67%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Stored cross-site scripting in Virtual Robots.txt before 1.10 allows remote authenticated users to inject scripts through the robots.txt field. The settings handler saves the User Agents and Directives field without sanitizing HTML and echoes the stored value into the plugin settings page. Administrator access is required, and a later settings-page view executes the injected script in the viewer's browser under the site's origin.

The record

CVE
CVE-2021-28121
Published
Aug 12, 2021
Updated
Aug 3, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-79, T1189
Attack vector
network
Privileges
admin

Timeline

How it unfolded

  1. Aug 12, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesadmin

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

9.8NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
7.5NVDAV:N/AC:L/Au:N/C:P/I:P/A:P
5.5WordfenceCVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:C/C:L/I:L/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesadmin
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1189Drive-by Compromise

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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