Linux Kernel: VLAN Insert Bug Triggers Uninit Slab Leakage (CVE202698377)
CVE-2026-98377 Published on October 9, 2026
vlan: require the MAC header to be present in __vlan_insert_inner_tag()
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.
Products Associated with CVE-2026-98377
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Affected Versions
Linux:- Version 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and below 40a5cc4b7251c74f3341332a226d02200e96bccf is affected.
- Version 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and below f42562dd027dc4ed103fae17b2206e73ea1963c4 is affected.
- Version 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and below 59af43ccece4d2d8b62e9e3ccc96b6e2e793bcdc is affected.
- Version 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and below ab888242fce4f16f6c4d4c6ec53939ad36aa3b3a is affected.
- Version 2.6.12 is affected.
- Before 2.6.12 is unaffected.
- Version 6.12.112, <= 6.12.* is unaffected.
- Version 6.18.55, <= 6.18.* is unaffected.
- Version 7.2.9, <= 7.2.* is unaffected.
- Version 7.3-rc5, <= * is unaffected.