---
id: "CVE-2026-126776"
page: "https://infrastack.ai/live/CVE-2026-126776"
kind: "vulnerability"
aliases: ["CVE-2026-126776"]
title: "SiYuan on Windows: crafted URL response writes files outside import folder"
severity: "medium"
cvss: 6.0
epss: null
exploited: false
status: "open"
category: "ai-tooling"
products: [{"name": "SiYuan", "fixed": [], "affected": "", "ecosystem": "vendor"}]
ecosystems: ["vendor"]
tags: ["ai-tooling", "mcp", "siyuan", "windows"]
not_affected_if: ["fixed-3.8.10", "mcp-fetch-tools-disabled", "not-windows"]
published_at: "2026-11-11T19:17:38+00:00"
first_seen_at: "2026-11-11T19:28:46+00:00"
updated_at: "2026-11-11T19:30:26+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-126776", "first_seen_at": "2026-11-11T19:28:46+00:00"}]
exploit_sources: []
---

# SiYuan on Windows: crafted URL response writes files outside import folder

Link for people: https://infrastack.ai/live/CVE-2026-126776 (this .md is for agents)

SiYuan's MCP web_fetch and http_request tools mishandle backslash-encoded filenames on Windows. An attacker who controls a URL those tools fetch can write chosen bytes to folders the SiYuan user can write to, outside the import directory.

_Summary, check and fix written by a model from the sources; labelled as such._

## Affected

- vendor:SiYuan affected range not listed fixed no fixed version listed

## How to check

- Check the SiYuan version on Windows; versions from `3.7.0` up to but not including `3.8.10` are affected.
- Check whether the MCP `web_fetch` or `http_request` tools are enabled in your SiYuan setup; the sources do not say how to confirm this.

## Fix

- SiYuan: upgrade to `3.8.10` or later.

## Timeline

- 2026-11-11T19:28:46+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-126776

## Documents

- [advisory] Vendor advisory: github.com https://github.com/siyuan-note/siyuan/security/advisories/GHSA-hq2c-hh95-vrr6
- [advisory] Third-party advisory: www.vulncheck.com https://www.vulncheck.com/advisories/siyuan-3.7.0-before-3.8.10-path-traversal-file-write-via-mcp-web-fetch
- [fix] Patch: github.com https://github.com/siyuan-note/siyuan/commit/94d6a42a0362c0a6938a29ab84addb1fe0aca21c
- [fix] Release notes: github.com https://github.com/siyuan-note/siyuan/releases/tag/v3.8.10

## From the sources

SiYuan 3.7.0 before 3.8.10 on Windows contains a path traversal vulnerability in kernel/util/webfetch.go that allows attackers to write files outside the import directory via backslash-encoded filenames. Attackers controlling a URL fetched by the MCP web_fetch or http_request tools can use %5C-encoded ..\ sequences to write chosen response bytes to directories above temp/import that are writable by the SiYuan user.

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