CVE-2026-21866Public exploitNetwork attack vector

Stored XSS via loose Mermaid rendering

Published Mar 3, 2026 · Updated Mar 3, 2026

Stored XSS in Mermaid chat rendering in LangGenius Dify before 1.11.2 allows remote authenticated users to execute script in shared chats. The Mermaid component renders untrusted diagram code with securityLevel set to loose and accepts click and initialization directives that create script-bearing SVG content. An attacker must create and share a malicious chat, and script execution occurs when another user views it, exposing that user's Dify session.

CVSS severity5.1
Medium
EPSS probability0.22%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Stored XSS in Mermaid chat rendering in LangGenius Dify before 1.11.2 allows remote authenticated users to execute script in shared chats. The Mermaid component renders untrusted diagram code with securityLevel set to loose and accepts click and initialization directives that create script-bearing SVG content. An attacker must create and share a malicious chat, and script execution occurs when another user views it, exposing that user's Dify session.

The record

CVE
CVE-2026-21866
Published
Mar 3, 2026
Updated
Mar 3, 2026
Vendor
LangGenius
Product
Dify
Classifications
CWE-79, T1059.007
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Mar 3, 2026CVE publishedPublication date reported by the CVE source.
  2. Mar 3, 2026Record 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=< 1.11.2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

LangGenius · Difyversion=< 1.11.2

Published CVSS scores

5.4NIST NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
5.1GitHub, Inc.CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:N/VI:N/VA:N/SC:L/SI:L/SA: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')
T1059.007JavaScript/JScript

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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