CVE-2021-43861Public exploitNetwork attack vector

Script execution via nested sequence-link URL scheme

Published Dec 30, 2021 · Updated Aug 4, 2024

Cross-site scripting in Mermaid before 8.13.8 allows remote authenticated users to execute JavaScript on a diagram reader's machine. The sequence-diagram link sanitizer removes one matching javascript: substring instead of validating the resulting URL, so a nested scheme survives. A victim must render an attacker-controlled diagram and follow the crafted actor link; execution occurs in the embedding page's browser context.

CVSS severity7.2
High
EPSS probability0.91%
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 Mermaid before 8.13.8 allows remote authenticated users to execute JavaScript on a diagram reader's machine. The sequence-diagram link sanitizer removes one matching javascript: substring instead of validating the resulting URL, so a nested scheme survives. A victim must render an attacker-controlled diagram and follow the crafted actor link; execution occurs in the embedding page's browser context.

The record

CVE
CVE-2021-43861
Published
Dec 30, 2021
Updated
Aug 4, 2024
Vendor
Mermaid
Product
Mermaid
Classifications
CWE-20, CWE-79, T1203
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Dec 30, 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

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

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

  1. Affected versionversion=< 8.13.8

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Mermaid · Mermaidversion=< 8.13.8

Published CVSS scores

7.2GitHubCVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H
5.4NIST NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
3.5NIST NVDAV:N/AC:M/Au:S/C:N/I:P/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-20Improper Input Validation
CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1203Exploitation for Client Execution

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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