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CVE-2026-84803

9.0 · CRITICAL

SiYuan before v3.8.2 contains a stored cross-site scripting vulnerability in asset serving due to an incomplete extension blocklist that misses script-capable file types.

Published Sep 2, 2026CWE-79EPSS 0.43%

Overview

CVE-2026-84803 is a critical-severity vulnerability. It was published on September 2, 2026 and has a CVSS 3.1 base score of 9.0 (CRITICAL).

This vulnerability has a CVSS 3.1 base score of 9.0, rated CRITICAL. It can be exploited remotely over the network. Some level of privileges is required for exploitation.

Technical description

SiYuan before v3.8.2 contains a stored cross-site scripting vulnerability in asset serving due to an incomplete extension blocklist that misses script-capable file types. Attackers can upload files with extensions like .xht, .ehtml, .xsl, .xbl, or .rdf that resolve to executable media types and execute JavaScript to steal API tokens and compromise workspaces.

Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

References

GitHubgithub.com/siyuan-note/siyuan/security/advisories/GHSA-7h8j-qw37-w46gRefwww.vulncheck.com/advisories/siyuan-before-3.8.2-stored-xss-via-incomplete-asset-blocklistGitHubgithub.com/siyuan-note/siyuan/security/advisories/GHSA-7h8j-qw37-w46g

How CyberStrike helps

Frequently asked questions

What is CVE-2026-84803?

CVE-2026-84803 is a critical-severity vulnerability. It was published on September 2, 2026 and has a CVSS 3.1 base score of 9.0 (CRITICAL).

How severe is CVE-2026-84803?

This vulnerability has a CVSS 3.1 base score of 9.0, rated CRITICAL. It can be exploited remotely over the network. Some level of privileges is required for exploitation.

How do I fix or remediate CVE-2026-84803?

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

How can CyberStrike help with CVE-2026-84803?

CyberStrike is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2026-84803 is actually reachable in your own applications and APIs, then verifies each finding before reporting it. That tells you if the weakness is a real, exploitable risk in your environment or a false positive you can safely deprioritize.

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