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A use-after-free vulnerability was found in the Linux kernel's IPv6 FIB rule lookup path. In fib6_rule_suppress(), when a route is suppressed and released via ip6_rt_put_flags(), the res->rt6 pointer is not cleared. If no later rule supplies a replacement route, fib6_rule_lookup() returns the stale (freed) rt6_info to its caller. The subsequent dst_release() then operates on freed memory, hitting rcuref_put_slowpath(). A local attacker who can configure IPv6 routing/FIB rules could trigger this to cause a denial of service (kernel crash) or potentially escalate privileges.
Upstream advisory: https://lore.kernel.org/linux-cve-announce/2026082100-CVE-2026-74581-47ca@gregkh/T/#u
The proposed mitigation does not appear to be applicable to the affected RHEL kernels because IPv6 is built directly into the kernel (`CONFIG_IPV6=y`), rather than provided as a loadable kernel module. Therefore, the following configuration cannot prevent the IPv6 subsystem from being loaded: install ipv6 /bin/true blacklist ipv6 Since there is no `ipv6.ko` module to blacklist when `CONFIG_IPV6=y`, this mitigation would not disable the vulnerable IPv6 code path. A kernel command-line parameter such as: ipv6.disable=1 would appear to be a more appropriate mitigation for completely disabling IPv6 on these kernels. Could you please confirm whether the current mitigation guidance is correct for RHEL kernels built with `CONFIG_IPV6=y`?