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Restrict empty packet frames from clients

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This commit is contained in:
Shane Freeder
2026-01-08 16:53:58 +00:00
parent 4bc3f00424
commit a03bd884aa
1 changed files with 8 additions and 0 deletions
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8
proxy/src/main/java/com/velocitypowered/proxy/protocol/netty/MinecraftVarintFrameDecoder.java
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@@ -44,6 +44,8 @@ public class MinecraftVarintFrameDecoder extends ByteToMessageDecoder {
+ "Velocity with -Dvelocity.packet-decode-logging=true to see more.");
private static final QuietDecoderException BAD_PACKET_LENGTH =
new QuietDecoderException("Bad packet length");
private static final QuietDecoderException INVALID_PREAMBLE =
new QuietDecoderException("Invalid packet preamble");
private static final QuietDecoderException VARINT_TOO_BIG =
new QuietDecoderException("VarInt too big");
private static final QuietDecoderException UNKNOWN_PACKET =
@@ -74,9 +76,15 @@ public class MinecraftVarintFrameDecoder extends ByteToMessageDecoder {
}
// skip any runs of 0x00 we might find
int wLength = in.readableBytes();
int packetStart = in.forEachByte(FIND_NON_NUL);
if (packetStart == -1) {
in.clear();
// Apply a more strict check in serverbound direction, we really shouldn't be seeing this many 0x00s
// even from the server, the only reason we even allow these is due to bugged servers
if (direction == ProtocolUtils.Direction.SERVERBOUND && wLength > 16) {
throw INVALID_PREAMBLE;
}
return;
}
in.readerIndex(packetStart);