## Summary `io.netty.incubator:netty-incubator-codec-bhttp` uses attacker-controlled Binary HTTP variable-length integers as `long` values but accumulates them into `int` offsets. Large valid varint lengths wrap the internal offset negative, leading to unchecked `ArrayIndexOutOfBoundsException` / `IndexOutOfBoundsException` from a tiny malformed BHTTP payload. A remote peer can trigger connection-level denial of service in applications that expose `BinaryHttpParser` / `BinaryHttpDecoder` to untrusted input. ## Details In `codec-bhttp/src/main/java/io/netty/incubator/codec/bhttp/BinaryHttpParser.java`, several parser paths store cumulative byte offsets in `int sumBytes` and then add attacker-controlled `long` lengths using compound assignment. In Java, `int += long` narrows the result back to `int`, so a length such as `2^31` wraps `sumBytes` negative. Primary request-control-data path: - `readRequestHead(...)` declares `int sumBytes = 0` at `BinaryHttpParser.java:386`. - It reads `methodLength` as a `long` at `BinaryHttpParser.java:394`. - It performs `sumBytes += methodLength` at `BinaryHttpParser.java:395`, narrowing the result to `int`. - If `methodLength` is `2^31`, `sumBytes` wraps negative and bypasses `if (sumBytes >= in.readableBytes()) return null` at `BinaryHttpParser.java:396-398`. - The parser then computes `schemeLengthIdx = in.readerIndex() + sumBytes` and calls `in.getByte(schemeLengthIdx)` at `BinaryHttpParser.java:401-402`, producing a negative index exception. The same pattern is present in header parsing: - `readFieldLine(...)` uses `int sumBytes` and adds `long nameLength` / `long valueLength` at `BinaryHttpParser.java:659-680`. - `valueLengthIdx = nameIdx + (int) nameLength` at `BinaryHttpParser.java:674` can also overflow. `getIndeterminateLength(...)` similarly uses `int sumBytes` and `long possibleTerminator` at `BinaryHttpParser.java:544-553`. ## Proof of concept Safe local verification performed in this repository. After compiling `codec-bhttp`, the following minimal verifier uses a 15-byte payload: ```java import io.netty.buffer.ByteBuf; import io.netty.buffer.Unpooled; import io.netty.incubator.codec.bhttp.BinaryHttpParser; public final class VerifyBhttpOverflow { public static void main(String[] args) { byte[] payload = new byte[] { 0x00, (byte)0xc0, 0x00, 0x00, 0x00, (byte)0x80, 0x00, 0x00, 0x00, 0x47, 0x45, 0x54, 0x58, 0x58, 0x58 }; ByteBuf input = Unpooled.wrappedBuffer(payload); try { new BinaryHttpParser(8192).parse(input, false); System.out.println("returned"); } catch (Throwable t) { System.out.println(t.getClass().getName()); System.out.println(t.getMessage()); } } } ``` Payload interpretation: - `00`: known-length request frame indicator. - `c000000080000000`: valid 8-byte varint encoding of `0x80000000` (`2^31`) as the method length. - `474554585858`: a few dummy bytes so the parser proceeds far enough to compute the next index. Observed result: ```text java.lang.ArrayIndexOutOfBoundsException Index -2147483639 out of bounds for length 15 ``` The parser should reject the malformed/incomplete message with a controlled decoder exception or return `null` awaiting more bytes; it should not allow integer wraparound to reach unchecked buffer indexing. ## Impact A remote peer can trigger an unchecked exception in the Binary HTTP decoder using a tiny payload. In typical Netty pipelines this closes or fails the affected channel. Depending on application-level exception handling, repeated payloads can cause sustained denial of service for exposed BHTTP endpoints. No memory corruption or information disclosure was observed because the failure occurs in Java/Netty bounds checks. ## Suggested remediation - Use `long` for all cumulative byte counts derived from protocol lengths. - Before converting any protocol length to `int`, verify it is non-negative, no larger than `Integer.MAX_VALUE`, and no larger than available readable bytes and configured limits. - Replace `sumBytes >= in.readableBytes()` checks with precise checked arithmetic that permits exact-boundary complete fields but rejects impossible lengths. - Throw a controlled `CorruptedFrameException` / `TooLongFrameException` for invalid or unsupported lengths. - Add regression tests for 8-byte varint lengths at and above `Integer.MAX_VALUE` in request control data, response control data, known and indeterminate field sections, and field lines. ## References - `codec-bhttp/src/main/java/io/netty/incubator/codec/bhttp/BinaryHttpParser.java:386-402` - `codec-bhttp/src/main/java/io/netty/incubator/codec/bhttp/BinaryHttpParser.java:659-680` - `codec-bhttp/src/main/java/io/netty/incubator/codec/bhttp/BinaryHttpParser.java:544-553` - RFC 9292: Binary Representation of HTTP Messages - RFC 9000 variable-length integer encoding