GHSA-mfg7-5gfp-c4w3 Netty: Memory Leak in DNS Record Decoder via Malformed Domain Names

• Maven io.netty:netty-codec-dns: >= 4.2.0.Final, < 4.2.16.Final → fixed in 4.2.16.Final • Maven io.netty:netty-codec-dns: < 4.1.136.Final → fixed in 4.1.136.Final

Summary A memory leak can be caused in Netty's DNS codec by sending malicious DNS packets containing invalid domain names. Because the leak occurs incrementally per packet, sustained malicious requests will cause a gradual Denial of Service. Details Inside `io.netty.handler.codec.dns.AbstractDnsRecord`, the parsed domain name string is passed to `IDN.toASCII(name)`. If the domain name contains characters that violate IDNA rules, `IDN.toASCII` throws an `IllegalArgumentException`. Because this exception occurs inside the constructor before the `DnsRecord` instance can assign the buffer to its content field for later release, the ByteBuf whose reference count was incremented (or newly allocated) is never released, resulting in a direct memory leak. There are several places where variants of this leak happen: • `io.netty.handler.codec.dns.DefaultDnsRecordDecoder#decodeRecord(java.lang.String, io.netty.handler.codec.dns.DnsRecordType, int, long, io.netty.buffer.ByteBuf, int, int)` invokes `in.retainedDuplicate()` or creates a new buffer `out` when constructing `DefaultDnsRawRecord` • `io.netty.handler.codec.dns.DnsCodecUtil#decompressDomainName` allocates a new `ByteBuf` and passes it to `encodeDomainName()`. If the decompressed domain name contains a null byte (`\0`), `encodeDomainName()` throws an `IllegalArgumentException`, leaking the newly allocated buffer. Impact Resource Exhaustion. Any application utilizing Netty's DnsRecordDecoder (such as DnsNameResolver or custom DNS servers) is vulnerable.