Linux Kernel up to 6.18.6 drivers/net/virtio_net.c hash_key_data[] uninitialized pointer

Summaryinfo

A vulnerability classified as critical was found in Linux Kernel up to 6.18.6. This affects an unknown function of the file drivers/net/virtio_net.c. Executing a manipulation of the argument hash_key_data[] can lead to uninitialized pointer. The identification of this vulnerability is CVE-2026-23143. There is no exploit available. Upgrading the affected component is advised.

Detailsinfo

A vulnerability classified as critical was found in Linux Kernel up to 6.18.6. This vulnerability affects an unknown function of the file drivers/net/virtio_net.c. The manipulation of the argument hash_key_data[] with an unknown input leads to a uninitialized pointer vulnerability. The CWE definition for the vulnerability is CWE-824. The product accesses or uses a pointer that has not been initialized. The impact remains unknown. CVE summarizes:

In the Linux kernel, the following vulnerability has been resolved: virtio_net: Fix misalignment bug in struct virtnet_info Use the new TRAILING_OVERLAP() helper to fix a misalignment bug along with the following warning: drivers/net/virtio_net.c:429:46: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end] This helper creates a union between a flexible-array member (FAM) and a set of members that would otherwise follow it (in this case `u8 rss_hash_key_data[VIRTIO_NET_RSS_MAX_KEY_SIZE];`). This overlays the trailing members (rss_hash_key_data) onto the FAM (hash_key_data) while keeping the FAM and the start of MEMBERS aligned. The static_assert() ensures this alignment remains. Notice that due to tail padding in flexible `struct virtio_net_rss_config_trailer`, `rss_trailer.hash_key_data` (at offset 83 in struct virtnet_info) and `rss_hash_key_data` (at offset 84 in struct virtnet_info) are misaligned by one byte. See below: struct virtio_net_rss_config_trailer { __le16 max_tx_vq; /* 0 2 */ __u8 hash_key_length; /* 2 1 */ __u8 hash_key_data[]; /* 3 0 */ /* size: 4, cachelines: 1, members: 3 */ /* padding: 1 */ /* last cacheline: 4 bytes */ }; struct virtnet_info { ... struct virtio_net_rss_config_trailer rss_trailer; /* 80 4 */ /* XXX last struct has 1 byte of padding */ u8 rss_hash_key_data[40]; /* 84 40 */ ... /* size: 832, cachelines: 13, members: 48 */ /* sum members: 801, holes: 8, sum holes: 31 */ /* paddings: 2, sum paddings: 5 */ }; After changes, those members are correctly aligned at offset 795: struct virtnet_info { ... union { struct virtio_net_rss_config_trailer rss_trailer; /* 792 4 */ struct { unsigned char __offset_to_hash_key_data[3]; /* 792 3 */ u8 rss_hash_key_data[40]; /* 795 40 */ }; /* 792 43 */ }; /* 792 44 */ ... /* size: 840, cachelines: 14, members: 47 */ /* sum members: 801, holes: 8, sum holes: 35 */ /* padding: 4 */ /* paddings: 1, sum paddings: 4 */ /* last cacheline: 8 bytes */ }; As a result, the RSS key passed to the device is shifted by 1 byte: the last byte is cut off, and instead a (possibly uninitialized) byte is added at the beginning. As a last note `struct virtio_net_rss_config_hdr *rss_hdr;` is also moved to the end, since it seems those three members should stick around together. :)

The advisory is shared for download at git.kernel.org. This vulnerability was named CVE-2026-23143 since 01/13/2026. There are known technical details, but no exploit is available. The current price for an exploit might be approx. USD $0-$5k (estimation calculated on 03/18/2026).

The vulnerability scanner Nessus provides a plugin with the ID 299319 (Linux Distros Unpatched Vulnerability : CVE-2026-23143), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 6.18.7 eliminates this vulnerability. Applying the patch ae48108c2310f1dd700e0dbb655c2f1d92ed00fc/4156c3745f06bc197094b9ee97a9584e69ed00bf is able to eliminate this problem. The bugfix is ready for download at git.kernel.org. The best possible mitigation is suggested to be upgrading to the latest version.

The vulnerability is also documented in the vulnerability database at Tenable (299319). VulDB is the best source for vulnerability data and more expert information about this specific topic.

Productinfo

Type

• Operating System

Vendor

• Linux

Name

• Kernel

Version

• 6.18.0
• 6.18.1
• 6.18.2
• 6.18.3
• 6.18.4
• 6.18.5
• 6.18.6

License

• open-source

Website

• Vendor: https://www.kernel.org/

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VulDB is the best source for vulnerability data and more expert information about this specific topic.

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