Linux Kernel up to 7.1.4 flowtable nft_dev_forward_path num_encaps out-of-bounds

Summaryinfo

A vulnerability labeled as very critical has been found in Linux Kernel up to 7.1.4. This affects the function nft_dev_forward_path of the component flowtable. Executing a manipulation of the argument num_encaps can lead to out-of-bounds. The identification of this vulnerability is CVE-2026-80634. The attack may be launched remotely. There is no exploit available.

Detailsinfo

A vulnerability was found in Linux Kernel up to 7.1.4. It has been declared as very critical. This vulnerability affects the function nft_dev_forward_path of the component flowtable. The manipulation of the argument num_encaps with an unknown input leads to a out-of-bounds vulnerability. The CWE definition for the vulnerability is CWE-125. The product reads data past the end, or before the beginning, of the intended buffer. As an impact it is known to affect confidentiality, integrity, and availability. CVE summarizes:

In the Linux kernel, the following vulnerability has been resolved: netfilter: flowtable: avoid num_encaps underflow on bridge VLAN untag The DEV_PATH_BR_VLAN_UNTAG case post-decrements info->num_encaps inside WARN_ON_ONCE(). num_encaps is u8, so if it's already 0 the decrement still happens and wraps it to 255. The break only leaves the inner switch -- a later path entry can set info->indev back to a real device, and we end up returning with num_encaps == 255. nft_dev_forward_path() then walks info.encap[] (size 2) up to num_encaps, which means an OOB stack read and a bogus count copied into the route descriptor. Should only happen on a malformed bridge path stack, hence the WARN, but worth handling sanely. Move the decrement out of the WARN. [ While at this, remove the WARN_ON_ONCE since this can only happen with a buggy bridge path stack --pablo ].

The advisory is available at git.kernel.org. This vulnerability was named CVE-2026-80634 since 08/26/2026. The exploitation appears to be easy. The attack can be initiated remotely. No form of authentication is required for a successful exploitation. Technical details are known, but there is no available exploit. The structure of the vulnerability defines a possible price range of USD $0-$5k at the moment (estimation calculated on 08/28/2026).

Upgrading to version 7.1.5 eliminates this vulnerability. Applying the patch 2f55fa28011c97d6495d5787808db10a8c2d690d/e052f920773b73be49eb4d8702a9f85de7464363 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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