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GHSA-xmv7-r254-6q78

MediumCVSS 6.8 / 10
Published Jun 8, 2026·Last modified Jun 8, 2026
Affected Components(0)

No affected components available

Description

Summary

Netty's DNS resolver uses a predictable PRNG for generating DNS transaction IDs and defaults to a static UDP source port. This combination reduces the entropy of DNS queries, enabling DNS Cache Poisoning (Kaminsky attack).

Details

Two factors contribute to this vulnerability in io.netty.resolver.dns:

  • Predictable Query IDs: DnsQueryIdSpace manages 16-bit transaction IDs in buckets of 16,384 IDs. It initializes only the first bucket. When an ID is returned, it is pushed back into the bucket at a random index generated by java.util.concurrent.ThreadLocalRandom:
Random random = ThreadLocalRandom.current();
int insertionPosition = random.nextInt(count + 1);

Because ThreadLocalRandom is a predictable LCG and the resolver operates within a single bucket, the sequence of IDs is predictable once the PRNG state is mathematically recovered.

  • Default Static Source Port: DnsNameResolverBuilder defaults to a channelStrategy of ChannelPerResolver. This binds the DatagramChannel once, resulting in a static source port for all subsequent queries.

Combined, a static source port and predictable transaction IDs reduces the entropy required to secure DNS resolution against spoofing.

Impact

DNS Cache Poisoning. Downstream applications using the default Netty DNS resolver may connect to malicious IPs, leading to traffic interception or MitM attacks.

Risk Scores
Base Score
6.8

The vulnerability can be exploited over the network without needing physical access. It is difficult for an attacker to exploit this vulnerability and may require special conditions. An attacker does not need any special privileges or access rights. No user interaction is needed for the attacker to exploit this vulnerability. The vulnerability can affect other systems as well, not just the initial system. There is a high impact on the integrity of the data.

Threat Intelligence
6.2

Exploitation attempts have been detected. Elevated vigilance and prompt remediation are advised.

EPSS
0.26%

The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.

Exploit
Not available

We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.

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Medium severity
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