security: safely parse YAML subscriptions (#3)

* security: safely parse YAML subscriptions

* security: load Clash YAML via SafeConstructor load() for type compatibility

* docs: clarify codePointLimit propagation via SafeConstructor

Author: hawkff

app/build.gradle.kts

@@ -66,7 +66,7 @@ dependencies {
     implementation("com.blacksquircle.ui:language-json:2.6.0")
 
     implementation("com.squareup.okhttp3:okhttp:5.0.0-alpha.3")
-    implementation("org.yaml:snakeyaml:1.30")
+    implementation("org.yaml:snakeyaml:2.3")
     implementation("com.github.daniel-stoneuk:material-about-library:3.2.0-rc01")
     implementation("com.jakewharton:process-phoenix:2.1.2")
     implementation("com.esotericsoftware:kryo:5.2.1")

app/src/main/java/io/nekohasekai/sagernet/group/RawUpdater.kt

@@ -32,8 +32,9 @@ import org.ini4j.Ini
 import org.json.JSONArray
 import org.json.JSONObject
 import org.json.JSONTokener
-import org.yaml.snakeyaml.TypeDescription
+import org.yaml.snakeyaml.LoaderOptions
 import org.yaml.snakeyaml.Yaml
+import org.yaml.snakeyaml.constructor.SafeConstructor
 import org.yaml.snakeyaml.error.YAMLException
 import java.io.StringReader
 import androidx.core.net.toUri
@@ -254,9 +255,23 @@ object RawUpdater : GroupUpdater() {
 
             try {
 
-                val yaml = Yaml().apply {
-                    addTypeDescription(TypeDescription(String::class.java, "str"))
-                }.loadAs(text, Map::class.java)
+                // Parse untrusted subscription YAML safely.
+                // SafeConstructor only produces standard types (Map/List/String/
+                // Number/Boolean/null) and rejects custom/global tags such as
+                // !!javax..., preventing arbitrary class instantiation
+                // (CVE-2022-1471 style gadget chains). A code-point limit bounds
+                // input size to mitigate decompression/billion-laughs style DoS.
+                // Note: load() is used instead of loadAs(..., Map::class.java)
+                // because SafeConstructor cannot construct an explicit root type
+                // tag; a YAML mapping is returned as a LinkedHashMap natively.
+                val loaderOptions = LoaderOptions().apply {
+                    codePointLimit = 10 * 1024 * 1024 // 10 MiB
+                }
+                // In SnakeYAML 2.x, Yaml(BaseConstructor) adopts the constructor's
+                // LoaderOptions (getLoadingConfig()), so codePointLimit set above is
+                // enforced during parsing (verified: input over the limit throws).
+                val yaml = Yaml(SafeConstructor(loaderOptions)).load<Any?>(text) as? Map<String, Any?>
+                    ?: error(app.getString(R.string.no_proxies_found_in_file))
 
                 val globalClientFingerprint = yaml["global-client-fingerprint"]?.toString() ?: ""