How severe is CVE-2026-21866?

CVE-2026-21866 has a CVSS 3.x base score of 5.4, rated medium severity. It is exploitable over network with low attack complexity, requires low privileges and user interaction. Impact on confidentiality is low, integrity low, and availability none.

Is CVE-2026-21866 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (12th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-21866?

CVE-2026-21866 affects Dify. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-21866?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

Does CVE-2026-21866 have an EU (EUVD) identifier?

Yes. CVE-2026-21866 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-9325.

When was CVE-2026-21866 published?

CVE-2026-21866 was published on 2026-03-03 and last updated on 2026-06-17.

CVE-2026-21866

CVE-2026-21866 is a medium-severity vulnerability in Dify with a CVSS 3.x base score of 5.4. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-79.

Key facts

Severity: Medium (CVSS 3.x base score 5.4)
CVSS v4: 5.1
EPSS exploit prediction: 0% (12th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-9325
Weakness: CWE-79
Affected product: Dify
Published: 2026-03-03
Last modified: 2026-06-17

Description

Dify is an open-source LLM app development platform. Prior to 1.11.2, Dify is vulnerable to a stored XSS issue when rendering Mermaid diagrams within chats. This occurs because Dify’s default Mermaid configuration uses securityLevel: loose, which allows potentially unsafe content to execute. This vulnerability is fixed in 1.11.2.

Frequently asked questions

What is CVE-2026-21866?: Dify is an open-source LLM app development platform. Prior to 1.11.2, Dify is vulnerable to a stored XSS issue when rendering Mermaid diagrams within chats. This occurs because Dify’s default Mermaid configuration uses securityLevel: loose, which allows potentially unsafe content to execute. This vulnerability is fixed in 1.11.2.
How severe is CVE-2026-21866?: CVE-2026-21866 has a CVSS 3.x base score of 5.4, rated medium severity. It is exploitable over network with low attack complexity, requires low privileges and user interaction. Impact on confidentiality is low, integrity low, and availability none.
Is CVE-2026-21866 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (12th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-21866?: CVE-2026-21866 affects Dify. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-21866?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2026-21866 have an EU (EUVD) identifier?: Yes. CVE-2026-21866 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-9325.
When was CVE-2026-21866 published?: CVE-2026-21866 was published on 2026-03-03 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:dify:dify:*:*:*:*:*:*:*:*

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