# CVE-2026-126776: SiYuan 3.7.0 before 3.8.10 Path Traversal File Write via MCP web_fetch

Status: published. Published: 2026-11-11. Updated: 2026-11-11.

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.

## Remediation

- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: CNA: VulnCheck) — https://github.com/siyuan-note/siyuan/commit/94d6a42a0362c0a6938a29ab84addb1fe0aca21c

## Affected products and versions

- siyuan-note / siyuan (github.com/siyuan-note/siyuan/kernel): ≥ 3.7.0; < 3.8.10 (affected, semver); 3.8.10 (unaffected, semver). Source: CNA: VulnCheck

## Severity and prioritization

- CVSS 4.0: 6 (medium); CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N; source: CNA: VulnCheck

- CVSS 3.1: 5.3 (medium); CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:H/A:N; source: CNA: VulnCheck

- CISA KEV: No listing in collected sources

- EPSS: Not available

- SSVC: Not available

- Weaknesses: CWE-22

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://github.com/siyuan-note/siyuan/security/advisories/GHSA-hq2c-hh95-vrr6 (CNA: VulnCheck; vendor-advisory)

- https://github.com/siyuan-note/siyuan/commit/94d6a42a0362c0a6938a29ab84addb1fe0aca21c (CNA: VulnCheck; patch)

- https://github.com/siyuan-note/siyuan/releases/tag/v3.8.10 (CNA: VulnCheck; release-notes)

- https://github.com/siyuan-note/siyuan/blob/v3.7.0/kernel/util/webfetch.go#L155 (CNA: VulnCheck; technical-description)

- https://www.vulncheck.com/advisories/siyuan-3.7.0-before-3.8.10-path-traversal-file-write-via-mcp-web-fetch (CNA: VulnCheck; third-party-advisory)

## Provenance

- CNA: VulnCheck: https://www.cve.org/CVERecord?id=CVE-2026-126776; retrieved 2026-11-11; source updated 2026-11-11

Revision: 8f01779c802207f2eb454d8fe812ef8d3390f64e2a402703e958ad8a7b8099d3

Canonical: https://y2.dev/cve/CVE-2026-126776

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