{"id":"CVE-2026-126776","kind":"vulnerability","aliases":["CVE-2026-126776"],"related":[],"title":"SiYuan on Windows: crafted URL response writes files outside import folder","description":"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.","summary":"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.","severity":"medium","cvss":6.0,"epss":null,"exploited":false,"exploited_at":null,"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"],"how_to_check":"- Check the SiYuan version on Windows; versions from `3.7.0` up to but not including `3.8.10` are affected.\n- 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.","status":"open","published_at":"2026-11-11T19:17:38+00:00","first_seen_at":"2026-11-11T19:28:46+00:00","triaged_at":"2026-11-11T19:30:26+00:00","updated_at":"2026-11-11T19:30:26+00:00","category":"ai-tooling","confidence":0.7,"triage":{"at":"2026-11-11T19:30:26Z","model":"claude-haiku-5-5","output":{"fix":"- SiYuan: upgrade to `3.8.10` or later.","reach":"internet","title":"SiYuan on Windows: crafted URL response writes files outside import folder","impact":"medium","summary":"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.","audience":"everyone","category":"ai-tooling","nicknames":[],"who_cares":["siyuan","windows","mcp"],"confidence":0.7,"fix_status":"available","needs_auth":"no","worst_case":"attacker writes chosen files outside the import folder","analyst_note":"","how_to_check":"- Check the SiYuan version on Windows; versions from `3.7.0` up to but not including `3.8.10` are affected.\n- 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.\n- unknown for any other check.","plain_action":"Update SiYuan to version 3.8.10 or later on your Windows computer.","product_name":"SiYuan","needs_analyst":false,"not_affected_if":["not-windows","fixed-3.8.10","mcp-fetch-tools-disabled"],"who_is_affected":"Only SiYuan on Windows in the affected range (3.7.0 before 3.8.10) is exposed, and the risk comes through the MCP web_fetch and http_request tools fetching an attacker-controlled URL. The sources do not say whether the tools are enabled by default, so check your configuration. Systems on other operating systems are not described as affected.","user_interaction":"unknown","product_ecosystem":"vendor","needs_special_setup":"yes","severity_if_unknown":"unknown"},"cost_usd":0.001372,"input_tokens":4686,"output_tokens":1806,"severity_before":"medium"},"analyst_status":null,"analyst_note":null,"search":"'-126776':14A,17A '-2026':13A,16A '3.7.0':67C '3.8.10':69C '5c':111C '5c-encoded':110C 'ai':20B 'ai-tool':19B 'allow':80C 'attack':42B,81C,94C 'backslash':36B,91C 'backslash-encod':35B,90C 'byte':53B,118C 'chosen':52B,116C 'contain':72C 'control':44B,95C 'craft':4A 'cve':12A,15A 'directori':65B,88C,120C 'encod':37B,92C,112C 'fetch':29B,49B,98C,103C 'file':8A,84C 'filenam':38B,93C 'folder':11A,55B 'http':31B,105C 'import':10A,64B,87C 'kernel/util/webfetch.go':78C 'mcp':22B,27B,101C 'mishandl':34B 'outsid':9A,62B,85C 'path':74C 'request':32B,106C 'respons':6A,117C 'sequenc':113C 'siyuan':1A,18A,23B,25B,57B,66C,128C 'temp/import':122C 'tool':21B,33B,48B,107C 'travers':75C 'url':5A,46B,97C 'use':109C 'user':58B,129C 'via':89C 'vulner':76C 'web':28B,102C 'window':3A,24B,40B,71C 'writabl':125C 'write':7A,51B,60B,83C,115C","nicknames":[],"mitigations":[],"who_affected":"Only SiYuan on Windows in the affected range (3.7.0 before 3.8.10) is exposed, and the risk comes through the MCP web_fetch and http_request tools fetching an attacker-controlled URL. The sources do not say whether the tools are enabled by default, so check your configuration. Systems on other operating systems are not described as affected.","tier":"B","verified":{},"analyst_revisit_at":null,"fix_status":"available","audience":"everyone","plain_action":"Update SiYuan to version 3.8.10 or later on your Windows computer.","pkeys":["siyuan"],"ptokens":["siyuan"],"labels":["aitooling","mcp","medium","siyuan","vendor","windows"],"campaign_type":null,"search_a":"'-126776':14A,17A '-2026':13A,16A 'craft':4A 'cve':12A,15A 'file':8A 'folder':11A 'import':10A 'outsid':9A 'respons':6A 'siyuan':1A,18A 'url':5A 'window':3A 'write':7A","search_b":"'ai':20B 'ai-tool':19B 'attack':42B 'backslash':36B 'backslash-encod':35B 'byte':53B 'chosen':52B 'control':44B 'directori':65B 'encod':37B 'fetch':29B,49B 'filenam':38B 'folder':55B 'http':31B 'import':64B 'mcp':22B,27B 'mishandl':34B 'outsid':62B 'request':32B 'siyuan':23B,25B,57B 'tool':21B,33B,48B 'url':46B 'user':58B 'web':28B 'window':24B,40B 'write':51B,60B","search_c":"'3.7.0':67C '3.8.10':69C '5c':111C '5c-encoded':110C 'allow':80C 'attack':81C,94C 'backslash':91C 'backslash-encod':90C 'byte':118C 'chosen':116C 'contain':72C 'control':95C 'directori':88C,120C 'encod':92C,112C 'fetch':98C,103C 'file':84C 'filenam':93C 'http':105C 'import':87C 'kernel/util/webfetch.go':78C 'mcp':101C 'outsid':85C 'path':74C 'request':106C 'respons':117C 'sequenc':113C 'siyuan':66C,128C 'temp/import':122C 'tool':107C 'travers':75C 'url':97C 'use':109C 'user':129C 'via':89C 'vulner':76C 'web':102C 'window':71C 'writabl':125C 'write':83C,115C","cause_entry":null,"cause_path":null,"disclosures_checked_at":null,"first_public_at":"2026-11-01T07:30:20+00:00","kev":null,"cvss_vector":"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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X","cvss_by":"disclosure@vulncheck.com","poc_count":0,"sources":[{"source":"nvd","external_id":"CVE-2026-126776","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-126776","severity":null,"published_at":"2026-11-11T19:17:38+00:00","modified_at":"2026-11-11T19:17:38+00:00","first_seen_at":"2026-11-11T19:28:46+00:00","fetched_at":"2026-11-11T19:28:46+00:00","note":null}],"documents":[{"id":128111,"url":"https://github.com/siyuan-note/siyuan/commit/94d6a42a0362c0a6938a29ab84addb1fe0aca21c","title":"Patch: github.com","kind":"other","source":"nvd","publisher":"vendor","text":null,"published_at":null,"relation":"fix","confidence":null,"note":"Patch: github.com"},{"id":128112,"url":"https://github.com/siyuan-note/siyuan/releases/tag/v3.8.10","title":"Release notes: github.com","kind":"release","source":"nvd","publisher":"vendor","text":null,"published_at":null,"relation":"fix","confidence":null,"note":"Release notes: github.com"},{"id":128113,"url":"https://github.com/siyuan-note/siyuan/security/advisories/GHSA-hq2c-hh95-vrr6","title":"Vendor advisory: github.com","kind":"vendor","source":"nvd","publisher":"vendor","text":null,"published_at":"2026-11-01T07:30:20+00:00","relation":"advisory","confidence":null,"note":"Vendor advisory: github.com"},{"id":128114,"url":"https://www.vulncheck.com/advisories/siyuan-3.7.0-before-3.8.10-path-traversal-file-write-via-mcp-web-fetch","title":"Third-party advisory: www.vulncheck.com","kind":"advisory","source":"nvd","publisher":"research","text":null,"published_at":null,"relation":"advisory","confidence":null,"note":"Third-party advisory: www.vulncheck.com"}],"disclosures":[],"exploit_sources":[],"notice":"Free to read, with fair use of about 60 pages a minute. For higher limits or API access: sales@infrastack.ai"}