fix: Crash when reading corrupted envelope (#4297)

Added a safe guard to prevent crashing when reading corrupted envelope

Author: brustolin

CHANGELOG.md

@@ -1,5 +1,12 @@
 # Changelog
 
+
+## Unreleased
+
+### Fixes
+
+- Crash when reading corrupted envelope (#4297)
+
 ## 8.35.0
 
 ### Features

Sources/Sentry/SentrySerialization.m

@@ -208,6 +208,14 @@ + (SentryEnvelope *_Nullable)envelopeWithData:(NSData *)data
             if (endOfEnvelope == i) {
                 i++; // 0 byte attachment
             }
+
+            if (bodyLength > 0 && data.length < (i + 1 + bodyLength)) {
+                SENTRY_LOG_ERROR(@"Envelope is corrupted or has invalid data. Trying to read %li "
+                                 @"bytes by skiping %li from a buffer of %li bytes.",
+                    (unsigned long)data.length, (unsigned long)bodyLength, (long)(i + 1));
+                return nil;
+            }
+
             NSData *itemBody = [data subdataWithRange:NSMakeRange(i + 1, bodyLength)];
             SentryEnvelopeItem *envelopeItem = [[SentryEnvelopeItem alloc] initWithHeader:itemHeader
                                                                                      data:itemBody];

Tests/SentryTests/Helper/SentrySerializationTests.swift

@@ -267,6 +267,17 @@ class SentrySerializationTests: XCTestCase {
         XCTAssertNil(actual)
     }
 
+    func testReturnNilForCorruptedEnvelope() throws {
+        let envelope = SentryEnvelope(event: Event(error: NSError(domain: "test", code: -1, userInfo: nil)))
+        let data = try XCTUnwrap(SentrySerialization.data(with: envelope))
+        
+        let corruptedData = data[0..<data.count - 1]
+        
+        let unserialized = SentrySerialization.envelope(with: corruptedData)
+        
+        XCTAssertNil(unserialized)
+    }
+    
     private func serializeEnvelope(envelope: SentryEnvelope) -> Data {
         var serializedEnvelope: Data = Data()
         do {