Public on 2024-01-17
Modified on 2024-02-02
When a router encounters an IPv6 packet too big to transmit to the next-hop, it returns an ICMP6 "Packet Too Big" (PTB) message to the sender. The sender caches this updated Maximum Transmission Unit (MTU) so it knows not to exceed this value when subsequently routing to the same host.

In Linux kernels prior to 6.3, garbage collection is run on the IPv6 Destination Route Cache if the number of entries exceeds a threshold when adding the destination to the cache. This garbage collection examines every entry in the cache while holding a lock. In these affected kernel versions, a flood of the IPv6 ICMP6 PTB messages could cause high lock contention and increased CPU usage, leading to a Denial-of-Service.

The fix backports the garbage collection improvements from Linux kernel 6.3 by bringing the IPv6 code closer to the IPv4 code, which does not have this issue.

Important severity
CVSS v3 Base Score
See breakdown

Affected Packages

Platform Package Release Date Advisory Status
Amazon Linux 1 kernel 2024-01-03 ALAS-2024-1899 Fixed
Amazon Linux 2 - Core kernel 2024-01-03 ALAS2-2024-2391 Fixed
Amazon Linux 2 - Kernel-5.10 Extra kernel 2024-01-05 ALAS2KERNEL-5.10-2024-045 Fixed
Amazon Linux 2 - Kernel-5.15 Extra kernel 2024-01-05 ALAS2KERNEL-5.15-2024-033 Fixed
Amazon Linux 2 - Kernel-5.4 Extra kernel 2024-01-03 ALAS2KERNEL-5.4-2024-057 Fixed
Amazon Linux 2023 kernel 2024-01-19 ALAS2023-2024-493 Fixed

CVSS Scores

Score Type Score Vector
Amazon Linux CVSSv3 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H