fix: harden Rust MediaFetcher agains redirect bypass and DNS rebinding

Cargo.toml

@@ -95,6 +95,7 @@ modelexpress-common = { version = "0.3.0" }
 
 humantime = { version = "2.2.0" }
 indexmap = { version = "2" }
+ipnet = { version = "2" }
 libc = { version = "0.2" }
 oneshot = { version = "0.1.13", features = ["std", "async"] }
 ordered-float = "4"

lib/bindings/python/rust/llm/preprocessor.rs

@@ -49,8 +49,11 @@ pub struct MediaFetcher {
 impl MediaFetcher {
     #[new]
     fn new() -> Self {
+        // Use from_env so DYN_MM_ALLOW_INTERNAL is honored by the
+        // Rust-side frontend-decode fetch path, matching the Python
+        // UrlValidationPolicy.from_env() behavior on the backend.
         Self {
-            inner: RsMediaFetcher::default(),
+            inner: RsMediaFetcher::from_env(),
         }
     }
     fn user_agent(&mut self, user_agent: String) {
@@ -65,6 +68,10 @@ impl MediaFetcher {
         self.inner.allow_direct_port = allow;
     }
 
+    fn allow_private_ips(&mut self, allow: bool) {
+        self.inner.allow_private_ips = allow;
+    }
+
     fn allowed_media_domains(&mut self, domains: Vec<String>) {
         self.inner.allowed_media_domains = Some(domains.into_iter().collect());
     }

lib/llm/Cargo.toml

@@ -76,6 +76,7 @@ either = { workspace = true }
 futures = { workspace = true }
 futures-util = { workspace = true }
 hf-hub = { workspace = true }
+ipnet = { workspace = true }
 rand = { workspace = true }
 oneshot = { workspace = true }
 parking_lot = { workspace = true }