# 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.

- **Severity:** Medium 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`)
- **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:** Yes
- **Published:** 10 Mar 2026
- **Updated:** 11 Mar 2026
- **Also known as:** GHSA-pmc9-f5qr-2pcr, GO-2026-4669

## 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 (Improper Neutralization of Input During Web Page Generation)

## 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 | Ecosystem | 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: B3log Siyuan.

## How do I fix CVE-2026-31809?

Upgrade github.com/siyuan-note/siyuan/kernel to 0.0.0-20260310025236-297bd526708f or later.

## 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:

- SiYuan <= v3.5.9 - Cross Site Scripting (nuclei): http/cves/2026/CVE-2026-31809.yaml

## Other vulnerabilities in B3log Siyuan

- [CVE-2026-32938](https://insights.sbomify.com/CVE-2026-32938/): SiYuan has an Arbitrary File Read in its Desktop Publish Service (critical 9.9)
- [CVE-2026-33669](https://insights.sbomify.com/CVE-2026-33669/): SiYuan has Arbitrary Document Reading within the Publishing Service (critical 9.8)
- [CVE-2026-33670](https://insights.sbomify.com/CVE-2026-33670/): SiYuan has directory traversal within its publishing service (critical 9.8)
- [CVE-2026-32767](https://insights.sbomify.com/CVE-2026-32767/): SiYuan: Authorization Bypass Allows Arbitrary SQL Execution via Search API (critical 9.8)
- [CVE-2024-53504](https://insights.sbomify.com/CVE-2024-53504/): SQL injection in n/a (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-31809 and fix it if it is affected.

What it is: 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.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-31809 exists.

Affected packages and fixed versions:
- github.com/siyuan-note/siyuan/kernel (Go): affected all versions; fixed in 0.0.0-20260310025236-297bd526708f
- github.com/siyuan-note/siyuan/kernel (Go): affected all versions; fixed in 0.0.0-20260310025236-297bd526708f
- github.com/siyuan-note/siyuan/kernel (Go): affected all versions; fixed in 0.0.0-20260310025236-297bd526708f

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-31809/ (Markdown: https://insights.sbomify.com/CVE-2026-31809/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-31809
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-31809
- OSV: https://osv.dev/vulnerability/CVE-2026-31809

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-31809/
Summaries are generated and may contain mistakes; the official description above is the record.