CVE-2026-100662 netty CVE debrief

Who should care

Defenders of systems using Netty's HTTP/3 codec, particularly those with exposure to untrusted or unauthenticated peers, should assess their exposure and prioritize remediation. This includes operators, platform administrators, vulnerability management teams, and security teams responsible for ensuring the security and stability of systems that utilize Netty's HTTP/3 codec.

Why it matters

CVE-2026-100662 is a high-severity vulnerability in Netty's HTTP/3 codec, allowing for denial of service via unbounded memory consumption. Defenders should assess exposure, prioritize remediation, and verify affected systems.

• Denial of service via OutOfMemoryError
• Unbounded per-connection heap growth
• Potential for system crashes or instability

Technical summary

The Netty HTTP/3 codec (io.netty:netty-codec-http3) versions 4.2.0.Final through 4.2.17.Final contain an uncontrolled resource consumption vulnerability. A remote, unauthenticated peer with an established HTTP/3 connection can declare a very large literal length, causing the ByteToMessageDecoder MERGE cumulator to retain and grow the per-connection buffer, ultimately triggering a large byte-array allocation. This leads to unbounded per-connection heap growth and OutOfMemoryError, resulting in denial of service.

Defensive priority

High

Recommended defensive actions

• Assess exposure of Netty HTTP/3 codec in your environment
• Prioritize remediation of affected Netty versions
• Verify system updates and patching
• Review compensating controls for exposed systems while remediation is scheduled and verified
• Check relevant monitoring, detection, and logs for exposed assets that need extra review
• Track exceptions, retest remediated assets, and close the item only after evidence is documented
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up

Evidence notes

The CVE record and NVD entry provide details on the vulnerability, including its description, CVSS score, and affected versions. The vulnerability is a high-severity issue in Netty's HTTP/3 codec, allowing for denial of service via unbounded memory consumption. Defenders should assess exposure, prioritize remediation, and verify affected systems. The existing HTTP/3 limits (maxHeaderListSize, maxUnknownFramePayloadLength, DEFAULT_MAX_FIELD_SECTION_SIZE) are not applied to this handler.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.