api: check_edge_access passes an unvalidated pubkey into the doublezero CLI argv

[karl-dz]

Summary

check_edge_access validates its public_ip input but not its pubkey input, then passes both as argv elements to the doublezero CLI. A pubkey that begins with a dash is read by the CLI as a flag rather than as a value for --user-payer.

This arrived in #770 (commit 472d815), which moved the access-pass lookup off ClickHouse and onto an exec of doublezero access-pass get --user-payer <pubkey> --client-ip <ip> --json. It is deliberately out of scope for that PR.

The handler trims pubkey and checks only that it is non-empty. The IP alongside it goes through net.ParseIP, a To4() check, and a re-serialize. The pubkey then reaches lookupEdgeAccessPass, which hands it to exec.CommandContext as an argv element.

Bounding the severity: exec.CommandContext takes an argument slice and does not involve a shell, so this is argument injection, not command injection, and there is no path to arbitrary command execution. What an MCP caller can do is steer the flags of the CLI invocation, for example by sending -h or --json as the pubkey, and get a confusing tool error or unintended CLI output in place of an access-pass lookup.

Fix

Validate the pubkey as a base58-encoded 32-byte value before the lookup call, rejecting it in the same shape as the existing empty-input and invalid-IP errors.

References

• Handler input checks:

  lake/api/handlers/mcp_onboarding.go

  Lines 306 to 317 in ef656fc

  	pubkey := strings.TrimSpace(input.Pubkey)
  	ip := strings.TrimSpace(input.PublicIP)
  	if pubkey == "" || ip == "" {
  	return nil, CheckEdgeAccessOutput{}, errors.New("both pubkey and public_ip are required")
  	}
  	parsed := net.ParseIP(ip)
  	if parsed == nil || parsed.To4() == nil {
  	return nil, CheckEdgeAccessOutput{}, errors.New("public_ip must be a valid IPv4 address")
  	}
  	ip = parsed.To4().String()
  	pass, err := a.lookupEdgeAccessPass(ctx, pubkey, ip)

• CLI invocation:

  lake/api/handlers/mcp_onboarding.go

  Line 352 in ef656fc

  out, err := run(ctx, "access-pass", "get", "--user-payer", userPayer, "--client-ip", publicIP, "--json")