CVE-2021-41165Network attack vector

Cross-site scripting via malformed HTML comments

Published Nov 17, 2021 · Updated Aug 4, 2024

Cross-site scripting in CKSource CKEditor 4 before 4.17.0 allows remote authenticated users to execute JavaScript through malformed comments. The core HTML processor accepts malformed comment markup that bypasses content sanitization, leaving attacker-supplied script executable. Exploitation requires low-privileged input access and user interaction, and script runs in the victim's browser context.

CVSS severity8.2
High
EPSS probability1.57%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Cross-site scripting in CKSource CKEditor 4 before 4.17.0 allows remote authenticated users to execute JavaScript through malformed comments. The core HTML processor accepts malformed comment markup that bypasses content sanitization, leaving attacker-supplied script executable. Exploitation requires low-privileged input access and user interaction, and script runs in the victim's browser context.

The record

CVE
CVE-2021-41165
Published
Nov 17, 2021
Updated
Aug 4, 2024
Vendor
CKSource
Product
CKEditor 4
Classifications
CWE-79, T1203
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Nov 17, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 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=< 4.17.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

CKSource · CKEditor 4version=< 4.17.0

Published CVSS scores

3.5NIST NVDAV:N/AC:M/Au:S/C:N/I:P/A:N
5.4NIST NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
8.2GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:L/A:L

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 exploitUnconfirmed

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1203Exploitation for Client Execution

Public exploit references

No public exploit references are available in this record.

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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