GHSA-mfg7-5gfp-c4w3 is a medium-severity (CVSS 5.3) CWE-772 vulnerability in io.netty:netty-codec-dns. O3 Security confirms whether GHSA-mfg7-5gfp-c4w3 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Netty: Memory Leak in DNS Record Decoder via Malformed Domain Names
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for GHSA-mfg7-5gfp-c4w3.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
GHSA-mfg7-5gfp-c4w3 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 371,256 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
io.netty:netty-codec-dns☕io.netty:netty-codec-dnsReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Maven packages — download data is not available via public APIs for these ecosystems.
Description
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)invokesin.retainedDuplicate()or creates a new bufferoutwhen constructingDefaultDnsRawRecordio.netty.handler.codec.dns.DnsCodecUtil#decompressDomainNameallocates a newByteBufand passes it toencodeDomainName(). If the decompressed domain name contains a null byte (\0),encodeDomainName()throws anIllegalArgumentException, leaking the newly allocated buffer.
Impact
Resource Exhaustion. Any application utilizing Netty's DnsRecordDecoder (such as DnsNameResolver or custom DNS servers) is vulnerable.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| ☕Maven | io.netty:netty-codec-dns | ≥ 4.2.0.Final&&< 4.2.16.Final | 4.2.16.Final |
| ☕Maven | io.netty:netty-codec-dns | all versions | 4.1.136.Final |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for io.netty:netty-codec-dns. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update io.netty:netty-codec-dns to 4.2.16.Final or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-mfg7-5gfp-c4w3 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether GHSA-mfg7-5gfp-c4w3 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-mfg7-5gfp-c4w3. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-mfg7-5gfp-c4w3 in your dependencies?
O3 detects GHSA-mfg7-5gfp-c4w3 across Maven dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.