{"id":"CVE-2026-126393","kind":"vulnerability","aliases":["CVE-2026-126393"],"related":[],"title":"SiYuan: skill-install download lets attackers reach internal services","description":"SiYuan before 3.8.10 contains a server-side request forgery vulnerability in the skill-install download path because fetchBytes performs only a parse-time hostname check instead of using ssrfSafeClient. Attackers can supply a skill URL via the MCP skill install action that redirects or DNS-rebinds to loopback addresses, reaching internal services and metadata endpoints.","summary":"SiYuan's skill-install download path checks the hostname only when parsing the URL, so redirects or DNS rebinding can send requests to loopback addresses. An attacker who can submit a skill URL through the MCP skill install action can reach internal services and cloud metadata endpoints.","severity":"medium","cvss":6.1,"epss":null,"exploited":false,"exploited_at":null,"products":[],"ecosystems":[],"tags":["mcp","package","self-hosted","siyuan"],"not_affected_if":["mcp-disabled","siyuan-3.8.10-or-later"],"how_to_check":"- Check the installed SiYuan version; affected builds are before `3.8.10`\n- Confirm whether the MCP skill install action is reachable from untrusted users","fix":"- SiYuan: upgrade to `3.8.10` or later","status":"open","published_at":"2026-11-13T10:17:43+00:00","first_seen_at":"2026-11-13T10:47:18+00:00","triaged_at":"2026-11-13T10:56:27+00:00","updated_at":"2026-11-13T10:56:27+00:00","category":"package","confidence":0.6,"triage":{"at":"2026-11-13T10:56:27Z","model":"claude-haiku-5-5","output":{"fix":"- SiYuan: upgrade to `3.8.10` or later","reach":"network","title":"SiYuan: skill-install download lets attackers reach internal services","impact":"medium","summary":"SiYuan's skill-install download path checks the hostname only when parsing the URL, so redirects or DNS rebinding can send requests to loopback addresses. An attacker who can submit a skill URL through the MCP skill install action can reach internal services and cloud metadata endpoints.","audience":"businesses","category":"package","nicknames":[],"who_cares":["siyuan","mcp","self-hosted"],"confidence":0.6,"fix_status":"available","needs_auth":"unknown","worst_case":"internal services and cloud metadata endpoints reachable from the server","analyst_note":"","how_to_check":"- Check the installed SiYuan version; affected builds are before `3.8.10`\n- Confirm whether the MCP skill install action is reachable from untrusted users\n- unknown for other configuration checks","plain_action":"","product_name":"","needs_analyst":false,"not_affected_if":["siyuan-3.8.10-or-later","mcp-disabled"],"who_is_affected":"Teams that run SiYuan with its MCP skill install action reachable, especially on servers that can reach internal services or cloud metadata endpoints. Single-user desktop installs without MCP exposure are less exposed. unknown whether other configurations are affected.","user_interaction":"no","product_ecosystem":"","needs_special_setup":"yes","severity_if_unknown":"medium"},"cost_usd":0.00073,"input_tokens":4619,"output_tokens":537,"severity_before":"medium"},"analyst_status":null,"analyst_note":null,"search":"'-126393':13A,16A '-2026':12A,15A '3.8.10':73C 'action':62B,114C 'address':48B,123C 'attack':7A,50B,103C 'check':30B,98C 'cloud':68B 'contain':74C 'cve':11A,14A 'dns':41B,119C 'dns-rebind':118C 'download':5A,28B,87C 'endpoint':70B,129C 'fetchbyt':90C 'forgeri':80C 'host':21B 'hostnam':32B,97C 'instal':4A,27B,61B,86C,113C 'instead':99C 'intern':9A,65B,125C 'let':6A 'loopback':47B,122C 'mcp':17B,59B,111C 'metadata':69B,128C 'packag':18B 'pars':35B,95C 'parse-tim':94C 'path':29B,88C 'perform':91C 'reach':8A,64B,124C 'rebind':42B,120C 'redirect':39B,116C 'request':45B,79C 'self':20B 'self-host':19B 'send':44B 'server':77C 'server-sid':76C 'servic':10A,66B,126C 'side':78C 'siyuan':1A,22B,23B,71C 'skill':3A,26B,55B,60B,85C,107C,112C 'skill-instal':2A,25B,84C 'ssrfsafecli':102C 'submit':53B 'suppli':105C 'time':96C 'url':37B,56B,108C 'use':101C 'via':109C 'vulner':81C","nicknames":[],"mitigations":[],"who_affected":"Teams that run SiYuan with its MCP skill install action reachable, especially on servers that can reach internal services or cloud metadata endpoints. Single-user desktop installs without MCP exposure are less exposed. unknown whether other configurations are affected.","tier":"C","verified":{},"analyst_revisit_at":null,"fix_status":"available","audience":"businesses","plain_action":null,"pkeys":[],"ptokens":[],"labels":["mcp","medium","package","selfhosted","siyuan"],"campaign_type":null,"search_a":"'-126393':13A,16A '-2026':12A,15A 'attack':7A 'cve':11A,14A 'download':5A 'instal':4A 'intern':9A 'let':6A 'reach':8A 'servic':10A 'siyuan':1A 'skill':3A 'skill-instal':2A","search_b":"'action':62B 'address':48B 'attack':50B 'check':30B 'cloud':68B 'dns':41B 'download':28B 'endpoint':70B 'host':21B 'hostnam':32B 'instal':27B,61B 'intern':65B 'loopback':47B 'mcp':17B,59B 'metadata':69B 'packag':18B 'pars':35B 'path':29B 'reach':64B 'rebind':42B 'redirect':39B 'request':45B 'self':20B 'self-host':19B 'send':44B 'servic':66B 'siyuan':22B,23B 'skill':26B,55B,60B 'skill-instal':25B 'submit':53B 'url':37B,56B","search_c":"'3.8.10':73C 'action':114C 'address':123C 'attack':103C 'check':98C 'contain':74C 'dns':119C 'dns-rebind':118C 'download':87C 'endpoint':129C 'fetchbyt':90C 'forgeri':80C 'hostnam':97C 'instal':86C,113C 'instead':99C 'intern':125C 'loopback':122C 'mcp':111C 'metadata':128C 'pars':95C 'parse-tim':94C 'path':88C 'perform':91C 'reach':124C 'rebind':120C 'redirect':116C 'request':79C 'server':77C 'server-sid':76C 'servic':126C 'side':78C 'siyuan':71C 'skill':85C,107C,112C 'skill-instal':84C 'ssrfsafecli':102C 'suppli':105C 'time':96C 'url':108C 'use':101C 'via':109C 'vulner':81C","cause_entry":null,"cause_path":null,"disclosures_checked_at":null,"first_public_at":"2026-10-29T13:59:13+00:00","kev":null,"cvss_vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:L/VI:L/VA:N/SC:L/SI:L/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-2026-126393","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-126393","severity":null,"published_at":"2026-11-13T10:17:43+00:00","modified_at":"2026-11-13T10:17:43+00:00","first_seen_at":"2026-11-13T10:47:18+00:00","fetched_at":"2026-11-13T10:47:18+00:00","note":null}],"documents":[{"id":145028,"url":"https://github.com/siyuan-note/siyuan/security/advisories/GHSA-6pg3-pqxw-jm82","title":"Vendor advisory: github.com","kind":"vendor","source":"nvd","publisher":"vendor","text":null,"published_at":"2026-10-29T13:59:13+00:00","relation":"advisory","confidence":null,"note":"Vendor advisory: github.com"},{"id":145029,"url":"https://www.vulncheck.com/advisories/siyuan-before-3.8.10-ssrf-via-skill-install-download-redirect-and-dns-rebinding","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"}