Strip CR/LF/NUL from every outbound s2s line

Free-form trailing text (message bodies, kick reasons, topics, metadata)
now passes through a single sanitizing choke-point in the serializer, so
no such text can carry an embedded line break that would smuggle a second
command onto the link. Line-based input closes the obvious path today,
but sanitizing at the point of serialization removes the whole class
regardless of where the text originated (federation, config, future
non-line sources).

inspircd/src/lib.rs

@@ -227,7 +227,7 @@ impl Protocol for InspIrcd {
     }
 
     fn serialize(&mut self, action: &NetAction) -> Vec<String> {
-        match action {
+        let lines = match action {
             NetAction::Burst => vec![self.sourced(format!("BURST {}", self.ts))],
             NetAction::EndBurst => vec![self.sourced("ENDBURST".to_string())],
             NetAction::Pong { token, from } => {
@@ -321,7 +321,12 @@ impl Protocol for InspIrcd {
             NetAction::Raw(s) => vec![s.clone()],
             // Internal: the link layer handles these before serialization.
             NetAction::DeferRegister { .. } | NetAction::DeferPassword { .. } | NetAction::SendEmail { .. } => vec![],
-        }
+        };
+        // A trailing parameter can carry free-form text (message bodies, kick
+        // reasons, topics, metadata). Strip CR/LF/NUL at this single choke-point
+        // so no such text — whatever its origin — can smuggle a second command
+        // onto the s2s link.
+        lines.into_iter().map(|l| l.replace(['\r', '\n', '\0'], "")).collect()
     }
 
     fn sid(&self) -> &str {
@@ -467,6 +472,19 @@ mod tests {
         assert_eq!(lines, vec![":42S ENCAP 0IR CHGIDENT 0IRAAAAAB cool".to_string()]);
     }
 
+    // Free-form text with embedded line breaks must not smuggle a second line
+    // onto the link: the serializer strips CR/LF/NUL from every outbound line.
+    #[test]
+    fn strips_crlf_from_trailing_text() {
+        let lines = proto().serialize(&NetAction::Notice {
+            from: "42SAAAAAA".into(),
+            to: "0IRAAAAAB".into(),
+            text: "hi\r\nKILL 0IRAAAAAB :pwned".into(),
+        });
+        assert_eq!(lines, vec![":42SAAAAAA NOTICE 0IRAAAAAB :hiKILL 0IRAAAAAB :pwned".to_string()]);
+        assert!(!lines[0].contains('\n') && !lines[0].contains('\r'));
+    }
+
     #[test]
     fn parses_ftopic_and_filters_own() {
         let ev = proto().parse(":0IRAAAAAB FTOPIC #chan 1783845132 1783845140 :Welcome all");