CVE-2021-3904Public exploitNetwork attack vector

Stored script execution via HTML5 entity bypass

Published Oct 27, 2021 · Updated Aug 3, 2024

Stored cross-site scripting in GetGrav Grav before 1.7.24 allows remote authenticated users to execute script in a viewer's browser. Security::detectXss decodes entities without HTML5 rules, leaving an encoded colon able to bypass the JavaScript-scheme check in an anchor href. Page-editing access is required to store the link, and a viewer must click it; execution remains within the site's browser origin.

CVSS severity6.3
Medium
EPSS probability0.59%
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 GetGrav Grav before 1.7.24 allows remote authenticated users to execute script in a viewer's browser. Security::detectXss decodes entities without HTML5 rules, leaving an encoded colon able to bypass the JavaScript-scheme check in an anchor href. Page-editing access is required to store the link, and a viewer must click it; execution remains within the site's browser origin.

The record

CVE
CVE-2021-3904
Published
Oct 27, 2021
Updated
Aug 3, 2024
Vendor
GetGrav
Product
Grav
Classifications
CWE-79, T1204.001
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Oct 27, 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?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=unspecified <1.7.24

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

GetGrav · Gravversion=unspecified <1.7.24

Published CVSS scores

6.3GitHub Advisory DatabaseCVSS:3.0/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:L
5.4GitLab Advisory DatabaseCVSS:3.1/AV:N/AC:L/PR:L/UI:R/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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

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
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1204.001User Execution: Malicious Link

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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