Summary

Ech0 implements link preview (editor fetches a page title) through GET /api/website/title. That is legitimate product behavior, but the implementation is unsafe: the route is unauthenticated, accepts a fully attacker-controlled URL, performs a server-side GET, reads the entire response body into memory (io.ReadAll). There is no host allowlist, no SSRF filter, and InsecureSkipVerify: true on the outbound client.

Attacker outcome : Anyone who can reach the instance can force the Ech0 server to open HTTP/HTTPS URLs of their choice as seen from the server’s network position (Docker bridge, VPC, localhost from the process view).
Go’s default http.Client follows redirects (unless disabled). Redirect chains can move the server-side request from an allowed-looking host to an internal target; the code does not disable this in SendRequest.

Affected Components

Ech0 codebase:

• internal/handler/common/common.go
  Handles the /api/website/title endpoint and accepts user-controlled URL input.

• internal/service/common/common.go
  Processes the request and invokes the outbound HTTP fetch (GetWebsiteTitle).

• internal/util/http/http.go
  Performs the HTTP request (SendRequest) with the following insecure configurations:

  • No URL validation or allowlist
  • Redirects enabled (default client behavior)
  • InsecureSkipVerify: true

PoC

Environment: Ech0 listening on http://127.0.0.1:6277 (e.g. Docker image sn0wl1n/ech0:latest). No cookies or Authorization header.

Step 1 — baseline: unauthenticated server-side fetch (public URL):

curl.exe -sS -m 20 "http://127.0.0.1:6277/api/website/title?website_url=https://example.com"

Observed result (verified): HTTP 200, JSON with code: 1 and data Example Domain — proves the Ech0 process performed an outbound GET without any client auth.

Step 2 — impact: host-bound page + recorded leak (repo PoC file)
Committed PoC page: poc_ssrf_proof.html

1. From poc file directory, listen on 0.0.0.0 (port 9999):

python -m http.server 9999 --bind 0.0.0.0

2. Docker Desktop (Windows / macOS): Ech0 in Docker fetches the host via host.docker.internal:

curl.exe -sS -m 20 "http://127.0.0.1:6277/api/website/title?website_url=http://host.docker.internal:9999/poc_ssrf_proof.html"

Recorded response (verified this workspace, Ech0 4.2.2 in Docker):

{"code":1,"msg":"获取网站标题成功","data":"ECH0_SSRF_POC_LEAK_2026"}

Python server log: GET /poc_ssrf_proof.html → 200 (proves the server/container pulled the page from your host).

Leak channel: the backend reads the full HTML body before parsing (see io.ReadAll in SendRequest).

Impact

• Verified: Unauthenticated callers can make the Ech0 process issue server-side HTTP(S) requests to internal/reserved targets reachable from that process (PoC Step 2: host-reachable listener reflected in JSON).
• Code-level: The full response is read into memory (io.ReadAll); only the title string is returned. Combined with default HTTP redirect following (standard http.Client behavior; not disabled here), the effective request graph is larger than a single URL.
• TLS: InsecureSkipVerify: true means misissued or intercepted TLS to internal HTTPS services is still accepted from the server’s perspective.
• Deployment-dependent: Where routing allows (typical cloud VMs), 169.254.169.254-class endpoints are in scope for the same code path; treat as *high.
• DOS(Denial of Service): reading the whole body into memory with io.ReadAll is a DoS vector if you point it at a massive file.

Remediation

• Enforce SSRF-safe URL policy: allow only needed schemes/hosts; block link-local, metadata, and loopback unless explicitly required.
• Remove InsecureSkipVerify; use normal TLS verification.
• Limit redirects (disable or cap hops; re-validate each target).
• Add response size / timeout limits; optionally restrict egress at the network layer.

References

• GHSA-wc4h-2348-jc3p