Linux Kernel up to 7.1.4 flowtable nf_flow_ip6_tunnel_proto encap_limit input validation

Summaryinfo

A vulnerability identified as very critical has been detected in Linux Kernel up to 7.1.4. This affects the function nf_flow_ip6_tunnel_proto of the component flowtable. The manipulation of the argument encap_limit leads to input validation. This vulnerability is traded as CVE-2026-72442. It is possible to initiate the attack remotely. There is no exploit available.

Detailsinfo

A vulnerability was found in Linux Kernel up to 7.1.4. It has been rated as very critical. This issue affects the function nf_flow_ip6_tunnel_proto of the component flowtable. The manipulation of the argument encap_limit with an unknown input leads to a input validation vulnerability. Using CWE to declare the problem leads to CWE-20. The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly. Impacted is confidentiality, integrity, and availability. The summary by CVE is:

In the Linux kernel, the following vulnerability has been resolved: netfilter: flowtable: fix and simplify IP6IP6 tunnel handling Fix nf_flow_ip6_tunnel_proto() to use pskb_may_pull() instead of skb_header_pointer() to ensure the outer IPv6 header is in the skb headroom, which is required for subsequent packet processing. Move ctx->offset update inside the IPPROTO_IPV6 conditional block since it should only be adjusted when an IP6IP6 tunnel is actually detected. Simplify the rx path by removing ipv6_skip_exthdr() and checking ip6h->nexthdr directly, as the flowtable fast path only handles simple IP6IP6 encapsulation without extension headers. Drop the tunnel encapsulation limit destination option support from the tx path to match, since the rx path no longer handles extension headers. Remove the encap_limit parameter from nf_flow_offload_ipv6_forward(), nf_flow_tunnel_ip6ip6_push() and nf_flow_tunnel_v6_push(), along with the ipv6_tel_txoption struct and related headroom/MTU adjustments.

It is possible to read the advisory at git.kernel.org. The identification of this vulnerability is CVE-2026-72442 since 08/09/2026. The exploitation is known to be easy. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. Technical details of the vulnerability are known, but there is no available exploit. The pricing for an exploit might be around USD $5k-$25k at the moment (estimation calculated on 08/15/2026).

Upgrading to version 7.1.5 or 7.2-rc1 eliminates this vulnerability. Applying the patch 7f8d816a9aa2729d270418f00c9ef5e85bfc1b31/f4c2d8668d85ed125985da663c824a9c25498257 is able to eliminate this problem.

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Productinfo

Type

• Operating System

Vendor

• Linux

Name

• Kernel

Version

• 7.1.0
• 7.1.1
• 7.1.2
• 7.1.3
• 7.1.4

License

• open-source

Website

• Vendor: https://www.kernel.org/

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