CVE-2026-99076 Linux CVE debrief

Who should care

Defenders responsible for Linux systems using IPv6 UDP should assess exposure and implement compensating controls. This includes reviewing system configurations, monitoring for suspicious activity, and applying patches as they become available.

Why it matters

A vulnerability in the Linux kernel's IPv6 UDP implementation could allow off-path attackers to conduct side-channel attacks. Defenders should assess exposure, implement compensating controls, and prioritize patching vulnerable systems.

• Off-path attackers may conduct side-channel attacks to discover ephemeral ports used by connected UDP sockets
• Defenders need to assess exposure and implement compensating controls for Linux systems using IPv6 UDP
• Patching vulnerable systems is necessary to prevent exploitation

Technical summary

The Linux kernel's IPv6 UDP implementation has a vulnerability that allows off-path attackers to conduct side-channel attacks to discover ephemeral ports used by connected UDP sockets. This is due to the kernel only creating exceptions in the IPv6 exception cache when ICMPv6 Packet Too Big and Redirect Message packets quote a UDP packet that can be matched to an existing socket. The kernel now creates exceptions before trying to find a matching socket, mitigating this issue.

Defensive priority

Defenders should prioritize assessing exposure and implementing compensating controls for Linux systems using IPv6 UDP. This involves reviewing system configurations, monitoring for suspicious activity, and applying patches as they become available.

Recommended defensive actions

• Assess Linux system configurations for IPv6 UDP usage
• Monitor for suspicious activity related to ICMPv6 Packet Too Big and Redirect Message packets
• Apply patches as they become available
• Review and update incident response plans
• Review compensating controls for exposed systems while remediation is scheduled and verified
• 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 source item provide details on the vulnerability, its impact, and potential mitigations. However, specific version information and exploitation details are limited. The Linux kernel's IPv6 UDP implementation has a vulnerability that allows off-path attackers to conduct side-channel attacks to discover ephemeral ports used by connected UDP sockets. This is due to the kernel only creating exceptions in the IPv6 exception cache when ICMPv6 Packet Too Big and Redirect Message packets quote a UDP packet that can be The

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.