siyuan-note/siyuan · error

failed to resolve host:

Error message

failed to resolve host: 

What it means

CheckHostSSRF performs a DNS lookup of the requested host before any outbound agent HTTP request (web_fetch / http_request) so it can block private/loopback addresses. If net.LookupIP fails — the hostname does not resolve, DNS is down, or the host string is malformed — the request is rejected with this error wrapping the resolver message.

Source

Thrown at kernel/util/httprequest.go:52

	"time"

	"github.com/siyuan-note/httpclient"
	golangProxy "golang.org/x/net/proxy"
)

const (
	maxHTTPRequestBytes     = 5 * 1024 * 1024  // text/html、text/plain、application/json 等文本类响应上限
	maxHTTPRequestFileBytes = 10 * 1024 * 1024 // 二进制响应落盘上限
	maxHTTPRequestChars     = 50000
)

// CheckHostSSRF 校验主机名解析出的 IP 不落在内网/回环等不可达地址段，
// 防止智能体被诱导发起 SSRF 攻击。web_fetch 与 http_request 共用此校验。
// https://github.com/siyuan-note/siyuan/security/advisories/GHSA-rg26-cg95-gq6p
func CheckHostSSRF(host string) error {
	ips, err := net.LookupIP(host)
	if err != nil {
		return errors.New("failed to resolve host: " + err.Error())
	}
	for _, ip := range ips {
		// 与 SSRFSafeDialer 共用 isPrivateIP，覆盖 NAT64、6to4、Teredo 等 IPv6 过渡地址。
		if isPrivateIP(ip) {
			return errors.New("access to private/internal IP is prohibited")
		}
	}
	return nil
}

// ssrfSafeClient 是智能体出站请求专用的 HTTP 客户端：直连时将目标固定到已校验的公网 IP，
// 使用代理时则先与用户配置的代理建立隧道，再通过隧道连接固定后的目标 IP，同时保留原始 Host 和 TLS SNI。
// 两种方式都不会在校验后再次按目标域名解析，避免 DNS 重绑定 TOCTOU 绕过。
// https://github.com/siyuan-note/siyuan/security/advisories/GHSA-x8gv-g2g3-65fj
var ssrfSafeClient = newSSRFSafeClient()

func newSSRFSafeClient() *http.Client {
	return newSSRFSafeClientWithResolver(net.DefaultResolver.LookupIPAddr)

View on GitHub (pinned to 8641553a1f)

Solutions

1. Verify the hostname spelling and that it is a real registered domain (dig/nslookup the host from the same machine)
2. Check the machine's DNS configuration (/etc/resolv.conf, systemd-resolved) and network connectivity
3. Retry once DNS is restored — this is a transient/environmental failure, not a policy block (a policy block returns the private-IP error instead)
4. If a local/hosts-file name is intended, it will still fail the SSRF policy by design; use the public domain instead

Example fix

// before
HTTPRequest(ctx, "https://exmaple.com/api") // typo, DNS fails
// after
HTTPRequest(ctx, "https://example.com/api")

addrs, err := net.LookupIP(host)
if err != nil || len(addrs) == 0 {
    return fmt.Errorf("host %q does not resolve; aborting request", host)
}

if err := CheckHostSSRF(host); err != nil {
    if strings.Contains(err.Error(), "failed to resolve host") {
        time.Sleep(retryBackoff)
        return retryFetch(url, 2)
    }
    return err // policy blocks are not retryable
}

When it happens

Trigger: HTTPRequest, WebFetch, downloadGeneratedImage, or downloadSkillSource called with a hostname that cannot be resolved: typo'd domain, expired domain, offline/filtered DNS, or a garbage host string.

Common situations: An AI agent hallucinating a URL; corporate DNS blocking external lookups; IPv6-only or sandboxed environments without resolv.conf; typo like 'htps://example.com' producing an unparseable host.

Related errors

• host has no public IP:
• host has no public IP: %s
• access to private/internal IP is prohibited
• host has no IP address:
• ip address [%s] is prohibited

AI-assisted analysis of siyuan-note/siyuan@8641553a1f (2026-09-11). Data as JSON: /api/errors/836b5c703117c5ba. Report an issue: GitHub.