{"id":"GHSA-mfg7-5gfp-c4w3","title":"Netty: Memory Leak in DNS Record Decoder via Malformed Domain Names","summary":"Netty: Memory Leak in DNS Record Decoder via Malformed Domain Names","severity":"medium","cvss":5.3,"cwe":["CWE-772"],"vendor":"netty","product":"io.netty:netty-codec-dns","ecosystem":"maven","affected":["io.netty:netty-codec-dns >= 4.2.0.Final, <= 4.2.15.Final","io.netty:netty-codec-dns <= 4.1.135.Final"],"patched":["io.netty:netty-codec-dns 4.2.16.Final","io.netty:netty-codec-dns 4.1.136.Final"],"published":"2026-07-24","updated":"2026-07-24","source":"GHSA","sourceUrl":"https://github.com/advisories/GHSA-mfg7-5gfp-c4w3","references":[{"url":"https://github.com/netty/netty/security/advisories/GHSA-mfg7-5gfp-c4w3"},{"url":"https://github.com/netty/netty/pull/17063"},{"url":"https://github.com/netty/netty/pull/17065"},{"url":"https://github.com/netty/netty/commit/5b68c61f37aa4a3045cba624cbea239655c9003b"},{"url":"https://github.com/netty/netty/commit/bb2ff68a1fb71cb4b0eb9a9e17b66c52aff680c6"},{"url":"https://github.com/netty/netty/releases/tag/netty-4.1.136.Final"},{"url":"https://github.com/netty/netty/releases/tag/netty-4.2.16.Final"},{"url":"https://github.com/advisories/GHSA-mfg7-5gfp-c4w3"}],"tags":["ghsa","maven"],"ingestedAt":"2026-07-24T17:34:27.507Z","slug":"GHSA-mfg7-5gfp-c4w3","body":"## Overview\n\n### Summary\nA 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.\n\n### Details\nInside `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`.\n\nBecause 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.\n\nThere are several places where variants of this leak happen:\n- `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`\n- `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.\n\n### Impact\nResource Exhaustion. Any application utilizing Netty's DnsRecordDecoder (such as DnsNameResolver or custom DNS servers) is vulnerable.\n\n## Affected packages\n\n- `io.netty:netty-codec-dns >= 4.2.0.Final, <= 4.2.15.Final`\n- `io.netty:netty-codec-dns <= 4.1.135.Final`\n\n## Remediation\n\nUpgrade to a patched release:\n\n- `io.netty:netty-codec-dns 4.2.16.Final`\n- `io.netty:netty-codec-dns 4.1.136.Final`","depth":"sunlit","depthScore":29,"depthScoreParts":{"impact":29.2,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}