CVE-2026-31809 SiYuan has a SVG Sanitizer Bypass via Whitespace in `javascript:` URI — Unauthenticated XSS
An attacker can execute arbitrary JavaScript via reflected XSS in SiYuan by bypassing SVG sanitization with whitespace characters in javascript URIs.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-31809?
CVE-2026-31809 is a medium-severity cross-site scripting vulnerability in B3log Siyuan, published on 10 Mar 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official description
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.
Weakness: CWE-79
Which versions are affected by CVE-2026-31809?
3 open source packages ship an affected version, including github.com/siyuan-note/siyuan/kernel. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
github.com/siyuan-note/siyuan/kernel Go | All versions | 0.0.0-20260310025236-297bd526708f |
github.com/siyuan-note/siyuan/kernel Go | All versions | 0.0.0-20260310025236-297bd526708f |
github.com/siyuan-note/siyuan/kernel Go | All versions | 0.0.0-20260310025236-297bd526708f |
Products include B3log Siyuan.
How do I fix CVE-2026-31809?
Upgrade github.com/siyuan-note/siyuan/kernel to 0.0.0-20260310025236-297bd526708f or later.
Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.
Is CVE-2026-31809 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-31809 exists.
Public exploit code: 1 Nuclei template.
Other vulnerabilities in B3log Siyuan
- CVE-2026-32938 SiYuan has an Arbitrary File Read in its Desktop Publish Service
- CVE-2026-33669 SiYuan has Arbitrary Document Reading within the Publishing Service
- CVE-2026-33670 SiYuan has directory traversal within its publishing service
- CVE-2026-32767 SiYuan: Authorization Bypass Allows Arbitrary SQL Execution via Search API
- CVE-2024-53504 SQL injection in n/a
Sources
Also known as GHSA-pmc9-f5qr-2pcr, GO-2026-4669.