# CVE-2026-126776: SiYuan path traversal in web fetch

Source: https://junglewise.ai/threats/cve-2026-126776-siyuan-3-7-0-before-3-8-10-on-windows-contains-a-path-traversal  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-11-11. Updated: 2026-11-11  
License: CC BY 4.0 with a link back

CVE-2026-126776 · Severity: medium · CVSS 5.3 · Published 2026-11-11

SiYuan is a personal knowledge management application that includes tools to fetch content from web URLs. A path traversal vulnerability in versions 3.7.0 through 3.8.9 on Windows allows attackers who control a URL fetched by the application to write files to any directory writable by the SiYuan user, potentially enabling arbitrary file write attacks or system compromise.

Technologies: [SiYuan](https://junglewise.ai/threats/technologies/siyuan). Vendors: [SiYuan](https://junglewise.ai/threats/vendors/siyuan).

## Quick answers

**Is CVE-2026-126776 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-126776 being exploited in the wild.

**How severe is CVE-2026-126776?** Medium severity, with a CVSS score of 5.3, published 11 November 2026.

**Which products and versions are affected?** SiYuan 3.7.0 to 3.8.9 on Windows.

**Is there a fix for CVE-2026-126776?** Yes: fixed in SiYuan 3.8.10. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-126776 attacked?** It is attacked over the network.

**Am I affected by CVE-2026-126776?** Check whether you run SiYuan at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- Fixed in SiYuan 3.8.10

## Technical details

The vulnerability exists in kernel/util/webfetch.go where filename extraction fails to properly validate backslash-encoded sequences (%5C) on Windows before writing downloaded files. An attacker controlling a fetched URL can craft responses with %5C-encoded ..\ sequences in the Content-Disposition filename or URL to traverse outside the intended temp/import directory. This affects the MCP web_fetch and http_request tools when handling non-HTML/non-text file downloads.

## Affected products

- SiYuan SiYuan 3.7.0 to 3.8.9 on Windows

## Timeline

- 2026-11-11: disclosed

## References

- [https://github.com/siyuan-note/siyuan/blob/v3.7.0/kernel/util/webfetch.go](https://github.com/siyuan-note/siyuan/blob/v3.7.0/kernel/util/webfetch.go)
- [https://github.com/siyuan-note/siyuan/commit/94d6a42a0362c0a6938a29ab84addb1fe0aca21c](https://github.com/siyuan-note/siyuan/commit/94d6a42a0362c0a6938a29ab84addb1fe0aca21c)

## Related threats

- [SiYuan publish filter information disclosure in local storage](https://junglewise.ai/threats/go-2026-6836-siyuan-the-publish-filter-for-local-storage-returns-the-7f022e62)
- [SiYuan path traversal via GLOBALROOT alias bypass](https://junglewise.ai/threats/cve-2026-118680-siyuan-3-8-7-through-3-8-8-fails-to-normalize-windows-globalroot)
- [SiYuan SQL injection in history search](https://junglewise.ai/threats/cve-2026-116170-siyuan-before-v3-8-7-contains-an-sql-injection-vulnerability)
- [SiYuan cross-site scripting in /check-auth redirect](https://junglewise.ai/threats/cve-2026-116167-siyuan-from-2-9-0-before-3-8-7-contains-a-cross-site-scripting)
- [SiYuan cleartext transmission via unenforced networkServeTLS setting](https://junglewise.ai/threats/cve-2026-116166-siyuan-3-6-0-before-3-8-7-accepts-and-persists-the)