UDP Socket Vulnerability in Linux Kernel

CVE-2026-99076

What is CVE-2026-99076?

In the Linux kernel, a vulnerability exists that allows off-path attackers to exploit the IPv6 exception cache. When ICMPv6 messages are locally delivered referencing a UDP packet, the exception cache is only updated if a UDP socket match occurs. This behavior opens a side-channel attack vector, enabling attackers to ascertain the ephemeral port used by UDP sockets. Previous mitigations aimed at obstructing hash collisions and randomizing exception storage were ineffective against this exploitation technique. A revised approach advises the creation of exceptions preemptively, regardless of socket matching, ensuring attackers can always observe cache updates, thus maintaining security integrity.

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