CVE Catalog

CVE-2026-98377

Unknown
Published: Translated: NVD NIST

Summary

In the Linux kernel, __vlan_insert_inner_tag() does not require the MAC header to be present before rewriting it. When a very short frame is sent through an IFF_TUN device, subsequent VLAN push operations can pull uninitialized slab bytes into the frame, leaking kernel memory.

Risk Assessment

Uninitialized kernel memory may leak to the network, potentially exposing sensitive data or aiding in bypassing security mechanisms such as ASLR.

Recommendation

Update the Linux kernel to a version with the fix requiring the MAC header to be present in __vlan_insert_inner_tag(). Restrict the ability to create IFF_TUN devices and send raw AF_PACKET frames to trusted users.

Other vulnerabilities in Linux kernel

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Original NVD description (English source)

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.

Vulnerability data from NVD (NIST) · CISA KEV · EPSS