CVE-2026-31809

moderate-risk
Published 2026-03-10

SiYuan is a personal knowledge management system. Prior to 3.5.10, SiYuan's SVG sanitizer (SanitizeSVG) checks href attributes for the javascript: prefix using strings.HasPrefix(). However, inserting ASCII tab (	), newline (
), or carriage return (
) characters inside the javascript: string bypasses this prefix check. Browsers strip these characters per the WHATWG URL specification before parsing the URL scheme, so the JavaScript still executes. This allows an attacker to inject executable JavaScript into the unauthenticated /api/icon/getDynamicIcon endpoint, creating a reflected XSS. This is a second bypass of the fix for CVE-2026-29183 (fixed in v3.5.9). This vulnerability is fixed in 3.5.10.

Do I need to act?

-
0.82% chance of exploitation
EPSS score — low exploit probability
-
Not on CISA KEV list
No confirmed active exploitation reported to CISA
?
Patch status unknown
Check vendor advisories for fix availability and mitigation guidance
6
CVSS 6.1/10 Medium
NETWORK / LOW complexity

Affected Products (1)

Affected Vendors

B3Log

References (1)

Exploit https://github.com/siyuan-note/siyuan/security/advisories/GHSA-pmc9-f5qr-2pcr
31
/ 100
moderate-risk
Severity 23/34 · High
Exploitability 3/34 · Minimal
Exposure 5/34 · Minimal