CVE-2026-31809
MediumPublic exploitSiYuan has a SVG Sanitizer Bypass via Whitespace in javascript: URI — Unauthenticated XSS
Published Mar 10, 2026 · Updated Aug 12, 2026 · Also known as GHSA-pmc9-f5qr-2pcr, GO-2026-4669
Key Facts
Routine patching- CVE-2026-31809 is a medium-severity vulnerability (CVSS 6.4 v4) affecting Siyuan (B3log), github.com/siyuan-note/siyuan/kernel (go).
- It is not listed in any known-exploited vulnerabilities catalog. Public exploit code is available.
- EPSS estimates a 0.6% probability of exploitation in the next 30 days.
- Fixed versions are available, including Siyuan 3.5.10, github.com/siyuan-note/siyuan/kernel 0.0.0-20260310025236-297bd526708f.
- Brandefense priority: routine patching, as no exploitation is known and its severity is moderate or low.
CVSS v4
6.4
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:N/SC:H/SI:H/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
EPSS (30-day exploit likelihood)
0.6%
Higher than 45.9% of all scored CVEs
Exploited in the wild
No known
Not in a known-exploited catalog
Public exploit code
Available
Proof-of-concept or weaponized module
Get the full CVE-2026-31809 brief as a PDF
Every affected product and fixed release, exploitation status and a first 24 hours response checklist, emailed within minutes.
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.
Affected Products
3 affected entries in total| Product | Affected versions | Fixed in |
|---|---|---|
| SiyuanB3log | >= < 3.5.10 | 3.5.10 |
| github.com/siyuan-note/siyuan/kernelgo | See advisory | 0.0.0-20260310025236-297bd526708f |
Patched Releases
Siyuan
3.5.10
github.com/siyuan-note/siyuan/kernel
0.0.0-20260310025236-297bd526708f
Timeline
Publicly disclosed
Mar 10, 2026
Last updated
Aug 12, 2026
Weakness Type
- CWE-79 Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
References
- advisoryGHSA advisory
- advisoryhttps://github.com/CVEProject/cvelistV5/tree/main/cves/2026/31xxx/CVE-2026-31809.json
- advisoryhttps://nvd.nist.gov/vuln/detail/CVE-2026-31809
- articlehttps://github.com/siyuan-note/siyuan/releases/tag/v3.5.10
- articlehttps://github.com/siyuan-note/siyuan/security/advisories/GHSA-pmc9-f5qr-2pcr
FAQ
Common Questions.
SiYuan is a personal knowledge management system.
Affected: Siyuan (B3log) versions >= < 3.5.10; github.com/siyuan-note/siyuan/kernel (go). The full list is in the CVE brief.
It is not listed in any known-exploited vulnerabilities catalog.
No, it is not currently listed in the CISA Known Exploited Vulnerabilities catalog.
Public exploit code is available.
Fixed versions are available, including Siyuan 3.5.10, github.com/siyuan-note/siyuan/kernel 0.0.0-20260310025236-297bd526708f.
Brandefense priority: routine patching, as no exploitation is known and its severity is moderate or low.
Is CVE-2026-31809 Running On Your Attack Surface?
Brandefense maps vulnerabilities like this one to your internet-facing assets and tells you exactly where to patch.
Request A Demo