CVE-2026-98377
Received Received - Intake

VLAN Tagging Memory Corruption in Linux Kernel

Publication date: 2026-10-09

Last updated on: 2026-10-09

Assigner: kernel.org

Description
In the Linux kernel, the following vulnerability has been resolved: vlan: require the MAC header to be present in __vlan_insert_inner_tag() __vlan_insert_inner_tag() only guarantees head room via skb_cow_head(), never that mac_len bytes of MAC header are present. Its ETH_HLEN wrappers - __vlan_insert_tag() under skb_vlan_push(), and vlan_insert_tag() under validate_xmit_vlan() on the generic transmit path - therefore rewrite the first 16 bytes at skb->data: a 12-byte memmove plus two 2-byte stores at +12 and +14. No caller supplies the bound, while the pop helpers use skb_ensure_writable()/pskb_may_pull(). An IFF_TUN device has hard_header_len == 0, so packet_snd() accepts a one-byte AF_PACKET/SOCK_RAW frame. The first vlan push only sets a hwaccel tag; the next - clsact "action vlan push" or bpf_skb_vlan_push() - enters the helper with skb->len still 1. The head comes from skbuff_small_head without __GFP_ZERO, so each push drags bytes from beyond skb->tail into the frame. After three the one-byte send leaves as 13 bytes carrying 11 bytes of uninitialised slab: 0000: 5a b3 62 12 80 88 ff ff 00 b3 62 12 81 `------------------------------' only 0x5a was sent; the rest is slab, here the top 56 bits of a linear-map address Require the MAC header the helper rewrites to be present, so such a frame is dropped rather than transmitted.

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Meta Information

Published
2026-10-09
Last Modified
2026-10-09
Generated
2026-10-09
AI Q&A
2026-10-09
EPSS Evaluated
N/A
NVD
CVE-2026-98377
EUVD
EUVD-2026-95532

Affected Vendors & Products

Showing 5 associated CPEs
Vendor Product Version / Range
Linux Linux 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2
Linux Linux 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2
Linux Linux 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2
Linux Linux 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2
Linux Linux 2.6.12

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Exploitability

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KEV
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CWE ID Description
CWE-UNKNOWN

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Executive Summary

This vulnerability in the Linux kernel involves a flaw in the VLAN tagging process where the function __vlan_insert_inner_tag() does not ensure the presence of the MAC header before modifying packet data. This can lead to memory corruption when processing small packets, particularly with IFF_TUN devices, causing uninitialized memory to be transmitted in network frames.

Impact Analysis

An attacker could exploit this to send malformed network packets that leak sensitive kernel memory, potentially exposing sensitive data or causing system instability. Systems using VLAN tagging or BPF filters may be affected if they process small packets.

Mitigation Strategies

Update the Linux kernel to the latest patched version to resolve the vlan tagging issue in __vlan_insert_inner_tag().

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