EUVD-2026-67686
GHSA-g42r-m263-958h
Severity by source
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:L/VA:N/SC:H/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
DNS rebinding requires attacker-controlled DNS infrastructure and TTL timing precision, warranting AC:H; UI:R because SiYuan must process attacker-supplied content; S:C reflects access to out-of-scope metadata and internal systems.
Primary rating from Vendor (VulnCheck).
CVSS VectorVendor: VulnCheck
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:L/VA:N/SC:H/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
Lifecycle Timeline
3DescriptionCVE.org
SiYuan versions before v3.8.1 contain a server-side request forgery vulnerability in the http_request and web_fetch agent tools that perform DNS resolution only at guard time without validating the connect-time resolution. Attackers can use DNS rebinding to answer the guard resolution with a public IP and the connect resolution with a private or metadata IP, bypassing the SSRF defense to access cloud instance metadata and internal services.
AnalysisAI
SiYuan before v3.8.1 exposes a DNS rebinding SSRF vulnerability in its http_request and web_fetch agent tools, allowing network-accessible attackers who can influence processed URLs to bypass the built-in SSRF IP-blocklist defense and reach cloud instance metadata services or internal network hosts. The guard-time-only DNS resolution creates a TOCTOU race: the SSRF check sees a legitimate public IP, but the actual TCP connection lands on 169.254.169.254 or another private address. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Exploitation requires three concurrent conditions: (1) the attacker can supply or influence a URL that SiYuan's http_request or web_fetch agent tools will process - for example, via a shared note, plugin configuration, or attacker-controlled content rendered by the application; (2) the attacker controls a DNS server for a domain they own and can manipulate DNS record TTLs to execute the rebinding timing race; (3) the SiYuan instance has network reachability to the target private or metadata IP, making cloud-hosted deployments with access to 169.254.169.254 the highest-risk scenario. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The CVSS 4.0 score of 8.4 is well-supported by the subsequent-system confidentiality impact (SC:H), which reflects the realistic threat of cloud credential theft via metadata service access - a severe outcome for any cloud-hosted SiYuan deployment. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | Full exploit scenario with step-by-step reproduction available after sign-in. |
| Remediation | Upgrade SiYuan to v3.8.1 or later to obtain the vendor-released patch per the advisory at https://github.com/siyuan-note/siyuan/security/advisories/GHSA-x8gv-g2g3-65fj. … Detailed patch versions, workarounds, and compensating controls in full report. |
Recommended ActionAI
Within 24 hours, identify all SiYuan instances and disable the http_request and web_fetch agent tools if not business-critical; isolate any internet-facing deployments. …
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External POC / Exploit Code
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