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Harden LNURL-auth request handling #862

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Harden LNURL-auth request handling #862

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9 changes: 8 additions & 1 deletion src/lnurl_auth.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -96,6 +96,13 @@ impl LnurlAuth {

let domain = url.base_url();

// Enforce HTTPS for non-localhost URLs per LNURL spec.
let is_localhost = domain == "localhost" || domain == "127.0.0.1" || domain == "[::1]";
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@tnull tnull Apr 2, 2026

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That's fine, but I do wonder if we should limit access to localhost/local network in general? Otherwise someone could prompt us to authenticate but have us make requests to arbitrary hosts, no? Maybe this method should take an expected hostname and abort if the decoded LNURL auth doesn't match that?

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@benthecarman benthecarman Apr 2, 2026

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I feel local host and private networks can still be useful for testing.

I don't think the expected host name would really work. Most things you are just scanning qr and authenticating in. It's not really the end of the world if you auth to the "wrong" place. Your auth key is tied to the domain so the only real threat would be if someone dns hijacked you or something.

if url.scheme() != "https" && !is_localhost {
log_error!(self.logger, "LNURL-auth URL must use HTTPS for non-localhost domains");
return Err(Error::InvalidLnurl);
}

// get query parameters for k1 and tag
let query_params: std::collections::HashMap<_, _> = url.query_pairs().collect();

Expand Down Expand Up @@ -135,7 +142,7 @@ impl LnurlAuth {
let auth_url = format!("{lnurl_auth_url}&sig={signature}&key={linking_public_key}");

log_debug!(self.logger, "Submitting LNURL-auth response");
let request = bitreq::get(&auth_url);
let request = bitreq::get(&auth_url).with_max_redirects(0);
let auth_response = self.client.send_async(request).await.map_err(|e| {
log_error!(self.logger, "Failed to submit LNURL-auth response: {e}");
Error::LnurlAuthFailed
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