CVE-2026-23398

A flaw was found in the Linux kernel. A remote attacker could trigger a kernel panic, leading to a Denial of Service (DoS), by sending a specially crafted Internet Control Message Protocol (ICMP) Fragmentation Needed error. This occurs when the system is configured for hardened Path Maximum Transmission Unit (PMTU) discovery mode and the ICMP error contains an inner IP header with an unregistered protocol number, causing a null pointer dereference.

This vulnerability requires the non-default kernel configuration ip_no_pmtu_disc=3 (hardened PMTU mode). Systems using the default PMTU discovery settings are not affected. While the attack is remotely triggerable via crafted ICMP packets, the specific configuration requirement significantly reduces the attack surface in typical deployments.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

Ensure ip_no_pmtu_disc is not set to 3. Check with: sysctl net.ipv4.ip_no_pmtu_disc. Values 0, 1, or 2 are not affected. If using value 3, consider temporarily switching to value 1 until a kernel update is applied.