Netty: DNS Cache Poisoning due to Predictable PRNG and Default Static Source Port

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

6.8 · CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:H/A:N

EPSS

• CVE-2026-45673: 0.32% estimated exploitation activity in the next 30 days; percentile 25.09 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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: 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…

Published by the source

8 Jun 2026, 23:02 UTC

Last modified by the source

12 Jun 2026, 19:29 UTC

Source last checked

26 Oct 2026, 16:46 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-xmv7-r254-6q78

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2026-45673

Advisory: Netty: DNS Cache Poisoning due to Predictable PRNG and Default Static Source Port
IDs: CVE-2026-45673, GHSA-xmv7-r254-6q78
Record: https://patchnext.com/advisories/cve-2026-45673 (revision 1, source checked 26 Oct 2026, 16:46 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.8)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: io.netty:netty-resolver-dns 4.2.15.Final, 4.1.135.Final. A vendor fix does not mean a deployment is fixed.

## Affected components
- Maven io.netty:netty-resolver-dns: affected >= 4.2.0.Final, <= 4.2.14.Final; <= 4.1.134.Final; fixed in 4.2.15.Final, 4.1.135.Final

## Suggested inspection (read-only)
- Maven io.netty:netty-resolver-dns: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on io.netty:netty-resolver-dns.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-xmv7-r254-6q78 (GitHub-reviewed advisory GHSA-xmv7-r254-6q78 lists affected ranges: Maven io.netty:netty-resolver-dns >=4.2.0.Final =0 <=4.1.134.Final)

Commands are suggestions: review each one before running it.