fix: block private image proxy requests

src-tauri/src/image_proxy.rs

@@ -0,0 +1,244 @@
+use reqwest::{blocking::Client, redirect::Policy, Url};
+use std::io::Read;
+use std::net::{IpAddr, Ipv4Addr, Ipv6Addr, SocketAddr, ToSocketAddrs};
+use std::time::Duration;
+
+const MAX_IMAGE_BYTES: u64 = 20 * 1024 * 1024;
+
+pub struct ImageResponse {
+    pub content_type: String,
+    pub body: Vec<u8>,
+}
+
+pub enum ProxyError {
+    Invalid(String),
+    Blocked(String),
+    Fetch(String),
+}
+
+impl ProxyError {
+    pub fn status(&self) -> u16 {
+        match self {
+            Self::Invalid(_) => 400,
+            Self::Blocked(_) => 403,
+            Self::Fetch(_) => 502,
+        }
+    }
+
+    pub fn message(&self) -> &str {
+        match self {
+            Self::Invalid(message) | Self::Blocked(message) | Self::Fetch(message) => message,
+        }
+    }
+}
+
+fn is_public_ipv4(ip: Ipv4Addr) -> bool {
+    let [a, b, c, _] = ip.octets();
+    !(a == 0
+        || a == 10
+        || a == 127
+        || a >= 224
+        || (a == 100 && (64..=127).contains(&b))
+        || (a == 169 && b == 254)
+        || (a == 172 && (16..=31).contains(&b))
+        || (a == 192 && b == 168)
+        || (a == 192 && b == 0 && c == 0)
+        || (a == 192 && b == 0 && c == 2)
+        || (a == 198 && (b == 18 || b == 19))
+        || (a == 198 && b == 51 && c == 100)
+        || (a == 203 && b == 0 && c == 113))
+}
+
+fn is_public_ipv6(ip: Ipv6Addr) -> bool {
+    if ip.is_unspecified() || ip.is_loopback() || ip.to_ipv4().is_some() {
+        return false;
+    }
+    let first = ip.segments()[0];
+    (0x2000..=0x3fff).contains(&first) && ip.segments()[..2] != [0x2001, 0x0db8]
+}
+
+fn is_public_ip(ip: IpAddr) -> bool {
+    match ip {
+        IpAddr::V4(ip) => is_public_ipv4(ip),
+        IpAddr::V6(ip) => is_public_ipv6(ip),
+    }
+}
+
+fn normalized_host(host: &str) -> String {
+    host.trim_start_matches('[')
+        .trim_end_matches(']')
+        .trim_end_matches('.')
+        .to_ascii_lowercase()
+}
+
+fn validate_url(raw_url: &str) -> Result<Url, ProxyError> {
+    let url = Url::parse(raw_url).map_err(|_| ProxyError::Invalid("Invalid image URL".into()))?;
+    if !matches!(url.scheme(), "http" | "https") {
+        return Err(ProxyError::Invalid(
+            "Only HTTP and HTTPS images are supported".into(),
+        ));
+    }
+    if !url.username().is_empty() || url.password().is_some() {
+        return Err(ProxyError::Invalid(
+            "Image URLs must not contain credentials".into(),
+        ));
+    }
+    let expected_port = if url.scheme() == "https" { 443 } else { 80 };
+    if url.port_or_known_default() != Some(expected_port) {
+        return Err(ProxyError::Blocked("Non-standard image URL port".into()));
+    }
+    let host = url
+        .host_str()
+        .ok_or_else(|| ProxyError::Invalid("Image URL has no host".into()))?;
+    if host.ends_with('.') {
+        return Err(ProxyError::Invalid(
+            "Image URL host must not have a trailing dot".into(),
+        ));
+    }
+    let normalized = normalized_host(host);
+    if normalized == "localhost" || normalized.ends_with(".localhost") {
+        return Err(ProxyError::Blocked(
+            "Local image hosts are not allowed".into(),
+        ));
+    }
+    if let Ok(ip) = normalized.parse::<IpAddr>() {
+        if !is_public_ip(ip) {
+            return Err(ProxyError::Blocked(
+                "Private image addresses are not allowed".into(),
+            ));
+        }
+    }
+    Ok(url)
+}
+
+fn resolve_public_host(url: &Url) -> Result<(String, Vec<SocketAddr>), ProxyError> {
+    let host = url
+        .host_str()
+        .ok_or_else(|| ProxyError::Invalid("Image URL has no host".into()))?;
+    let host = normalized_host(host);
+    let port = url
+        .port_or_known_default()
+        .ok_or_else(|| ProxyError::Invalid("Image URL has no port".into()))?;
+    let addresses: Vec<_> = (host.as_str(), port)
+        .to_socket_addrs()
+        .map_err(|error| ProxyError::Fetch(format!("Could not resolve image host: {error}")))?
+        .collect();
+    if addresses.is_empty() {
+        return Err(ProxyError::Fetch(
+            "Image host resolved to no addresses".into(),
+        ));
+    }
+    if addresses.iter().any(|address| !is_public_ip(address.ip())) {
+        return Err(ProxyError::Blocked(
+            "Image host resolves to a private address".into(),
+        ));
+    }
+    Ok((host, addresses))
+}
+
+fn image_client(host: &str, addresses: &[SocketAddr]) -> Result<Client, ProxyError> {
+    let redirect_host = host.to_string();
+    Client::builder()
+        .timeout(Duration::from_secs(30))
+        .redirect(Policy::custom(move |attempt| {
+            if attempt.previous().len() >= 5
+                || attempt
+                    .url()
+                    .host_str()
+                    .map_or(true, |host| normalized_host(host) != redirect_host)
+                || validate_url(attempt.url().as_str()).is_err()
+            {
+                attempt.stop()
+            } else {
+                attempt.follow()
+            }
+        }))
+        .resolve_to_addrs(host, addresses)
+        .build()
+        .map_err(|error| ProxyError::Fetch(format!("Could not create image client: {error}")))
+}
+
+pub fn fetch(raw_url: &str) -> Result<ImageResponse, ProxyError> {
+    let url = validate_url(raw_url)?;
+    let (host, addresses) = resolve_public_host(&url)?;
+    let client = image_client(&host, &addresses)?;
+    let mut response = client
+        .get(url)
+        .send()
+        .map_err(|error| ProxyError::Fetch(format!("Image request failed: {error}")))?;
+    if !response.status().is_success() {
+        return Err(ProxyError::Fetch(format!(
+            "Image server returned {}",
+            response.status()
+        )));
+    }
+    if response
+        .content_length()
+        .is_some_and(|length| length > MAX_IMAGE_BYTES)
+    {
+        return Err(ProxyError::Blocked("Image exceeds the 20 MiB limit".into()));
+    }
+    let content_type = response
+        .headers()
+        .get(reqwest::header::CONTENT_TYPE)
+        .and_then(|value| value.to_str().ok())
+        .unwrap_or("")
+        .to_string();
+    if !content_type.to_ascii_lowercase().starts_with("image/") {
+        return Err(ProxyError::Blocked(
+            "Remote resource is not an image".into(),
+        ));
+    }
+    let mut body = Vec::new();
+    response
+        .by_ref()
+        .take(MAX_IMAGE_BYTES + 1)
+        .read_to_end(&mut body)
+        .map_err(|error| ProxyError::Fetch(format!("Could not read image: {error}")))?;
+    if body.len() as u64 > MAX_IMAGE_BYTES {
+        return Err(ProxyError::Blocked("Image exceeds the 20 MiB limit".into()));
+    }
+    Ok(ImageResponse { content_type, body })
+}
+
+#[cfg(test)]
+mod tests {
+    use super::{is_public_ip, validate_url};
+    use std::net::{IpAddr, Ipv4Addr, Ipv6Addr};
+
+    #[test]
+    fn blocks_local_and_private_networks() {
+        for ip in [
+            IpAddr::V4(Ipv4Addr::LOCALHOST),
+            IpAddr::V4(Ipv4Addr::new(10, 0, 0, 1)),
+            IpAddr::V4(Ipv4Addr::new(169, 254, 169, 254)),
+            IpAddr::V4(Ipv4Addr::new(192, 168, 1, 1)),
+            IpAddr::V6(Ipv6Addr::LOCALHOST),
+            "fc00::1".parse().unwrap(),
+            "fe80::1".parse().unwrap(),
+        ] {
+            assert!(!is_public_ip(ip), "{ip}");
+        }
+        assert!(is_public_ip("93.184.216.34".parse().unwrap()));
+        assert!(is_public_ip(
+            "2606:2800:220:1:248:1893:25c8:1946".parse().unwrap()
+        ));
+    }
+
+    #[test]
+    fn validates_only_public_web_image_urls() {
+        for url in [
+            "file:///etc/passwd",
+            "http://localhost/image.png",
+            "http://127.0.0.1/image.png",
+            "http://[::1]/image.png",
+            "http://example.com:8080/image.png",
+            "https://example.com./image.png",
+            "https://user:pass@example.com/image.png",
+        ] {
+            assert!(validate_url(url).is_err(), "{url}");
+        }
+        assert!(validate_url("https://example.com/image.png").is_ok());
+        assert!(validate_url("http://93.184.216.34/image.png").is_ok());
+    }
+}

src-tauri/src/lib.rs

@@ -3,6 +3,7 @@ mod asset_scope;
 mod backup;
 mod commands;
 mod history;
+mod image_proxy;
 mod search;
 mod state;
 mod sync;
@@ -252,72 +253,21 @@ pub fn run() {
             std::thread::spawn(move || {
                 let encoded = path.strip_prefix('/').unwrap_or(&path);
                 let external_url = percent_decode(encoded);
-
-                if !external_url.starts_with("http://") && !external_url.starts_with("https://") {
-                    responder.respond(
+                let response = match image_proxy::fetch(&external_url) {
+                    Ok(image) => tauri::http::Response::builder()
+                        .status(200)
+                        .header("Content-Type", image.content_type)
+                        .header("Access-Control-Allow-Origin", "*")
+                        .header("X-Content-Type-Options", "nosniff")
+                        .body(image.body),
+                    Err(error) => {
+                        log::warn!("Blocked external image request: {}", error.message());
                         tauri::http::Response::builder()
-                            .status(400)
+                            .status(error.status())
                             .body(Vec::new())
-                            .unwrap(),
-                    );
-                    return;
-                }
-
-                let client = match reqwest::blocking::Client::builder()
-                    .timeout(std::time::Duration::from_secs(30))
-                    .build()
-                {
-                    Ok(c) => c,
-                    Err(_) => {
-                        responder.respond(
-                            tauri::http::Response::builder()
-                                .status(502)
-                                .body(Vec::new())
-                                .unwrap(),
-                        );
-                        return;
                     }
                 };
-
-                match client.get(&external_url).send() {
-                    Ok(resp) => {
-                        let content_type = resp
-                            .headers()
-                            .get("content-type")
-                            .and_then(|h| h.to_str().ok())
-                            .unwrap_or("application/octet-stream")
-                            .to_string();
-                        let status = resp.status().as_u16();
-                        match resp.bytes() {
-                            Ok(bytes) => {
-                                responder.respond(
-                                    tauri::http::Response::builder()
-                                        .status(status)
-                                        .header("Content-Type", &content_type)
-                                        .header("Access-Control-Allow-Origin", "*")
-                                        .body(bytes.to_vec())
-                                        .unwrap(),
-                                );
-                            }
-                            Err(_) => {
-                                responder.respond(
-                                    tauri::http::Response::builder()
-                                        .status(502)
-                                        .body(Vec::new())
-                                        .unwrap(),
-                                );
-                            }
-                        }
-                    }
-                    Err(_) => {
-                        responder.respond(
-                            tauri::http::Response::builder()
-                                .status(502)
-                                .body(Vec::new())
-                                .unwrap(),
-                        );
-                    }
-                }
+                responder.respond(response.expect("valid image proxy response"));
             });
         });