CVE-2026-82234: SiYuan before v3.8.1 SSRF via DNS-Rebinding TOCTOU
SiYuan versions before v3.8.1 contain a server-side request forgery vulnerability in the httprequest and webfetch 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.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
SiYuan http_request and web_fetch agent toolsto a version that resolves this vulnerability.Fixed in 3.8.1 - Compensating control
Because the SSRF defense only performs DNS resolution at guard time without validating the connect-time resolution (DNS-Rebinding TOCTOU), restrict egress/network access from the SiYuan instance to prevent it from reaching private IPs and cloud metadata service endpoints.
Event History
Frequently Asked Questions
Which deployments are exposed?
SiYuan versions before v3.8.1 are affected where the http_request or web_fetch agent tools can be induced to make requests to attacker-controlled hostnames.
What does an attacker need to exploit this issue?
An attacker needs to cause a vulnerable agent tool to request a hostname whose DNS answers can be changed between the initial guard-time lookup and the later connection-time lookup. No privileges are required, but user interaction is required according to the supplied severity vector.
What can an attacker reach through the bypass?
The DNS-rebinding bypass can allow requests to private IP addresses, cloud instance metadata endpoints, and internal services that the SSRF defense was intended to block.
What is the remediation?
Upgrade SiYuan to v3.8.1 or later. The affected versions are those before v3.8.1.