High [CVE-2026-74724] avoid out-of-bounds write in ip_vs_nat_icmp

In the Linux kernel, the following vulnerability has been resolved: ipvs: avoid out-of-bounds write in ip_vs_nat_icmp Sashiko warns that local attacker can modify the packet while it is processed by IPVS. Some places read the IP ihl field multiple times which can cause out-of-bounds access.

One such place is ip_vs_nat_icmp where we can write after the validated area. Fix it by providing ciph argument just like it is done for IPv6 and use ciph->len as offset to the embedded transport header.

Modify some IPv4 header checks by reading the ihl field only once. A flaw was found in the Linux kernel's IPVS (IP Virtual Server) component.

A local attacker can exploit this vulnerability by manipulating packets processed by IPVS, specifically within the `ip_vs_nat_icmp` function. This manipulation can lead to an out-of-bounds write due to improper handling of the IP header length field.

This allows the attacker to write data beyond the intended memory area, potentially corrupting data or leading to further system compromise. Red Hat severity: Moderate — CVSS 7 (CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H).

Weakness: CWE-787. Affected Red Hat products: Red Hat Enterprise Linux 10; Red Hat Enterprise Linux 6; Red Hat Enterprise Linux 7; Red Hat Enterprise Linux 8; Red Hat Enterprise Linux 9.

Will not fix / out of support: Red Hat Enterprise Linux 6.