SiYuan 3.7.0 before 3.8.10 Path Traversal File Write via MCP web_fetch

CVE-2026-126776

What is CVE-2026-126776?

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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