CVE-2026-81000

net: tun: bound receive headroom

State: Published
Severity: 7.8 High
Published: Sep 11, 2026
Updated: Oct 19, 2026
Reserved: Aug 26, 2026

Description

In the Linux kernel, the following vulnerability has been resolved:

net: tun: bound receive headroom

tun_get_user() uses tun->align both as skb headroom and when choosing how much packet data to keep linear. OVS can propagate an oversized headroom request from another port to TUN or TAP.

When align is larger than the usable space in a one-page skb head, SKB_MAX_HEAD(align) underflows and the result becomes negative when stored in good_linear. That value later wraps when assigned to the size_t linear variable, and tun_alloc_skb() can place skb->data outside the allocated head.

Bound the headroom stored by TUN to the one-page skb-head budget and the largest non-sentinel 16-bit skb header offset. Leave one linear byte for raw TUN and a complete Ethernet header for TAP, including NET_IP_ALIGN.

Also pull the raw-TUN protocol byte and the TAP Ethernet header before accessing them, so these checks remain safe for nonlinear skbs supplied by other allocation paths.

Scores

CVSS	Score	Vector	Source
3.1	7.8 High	CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H	Linux

Weaknesses

The record names no weakness.

Affected Products

Product	Versions
LinuxLinux	eaea34b23c46bf17b4a5638be69ab3561854f34b to before ad715e713610d2d5473c3a6498c825ccecf26491Affected eaea34b23c46bf17b4a5638be69ab3561854f34b to before 708e87937de93f445225c134a2e20519f9b4ce60Affected eaea34b23c46bf17b4a5638be69ab3561854f34b to before 18ef24cdb2eba32e38f1d27f2d02b7b4212e8f76Affected eaea34b23c46bf17b4a5638be69ab3561854f34b to before 010eee265d6bd8769b6a523d2a0693d9b3f5df43Affected eaea34b23c46bf17b4a5638be69ab3561854f34b to before 379d85c7f25f3e05a428225e6b8a65613c6e9b9dAffected eaea34b23c46bf17b4a5638be69ab3561854f34b to before e098d9cc8859614a7f7baebc96e32a5a16b18ed2Affected eaea34b23c46bf17b4a5638be69ab3561854f34b to before 0ada54ea63e48b9c1608e917ccb7dfadbe86db28Affected eaea34b23c46bf17b4a5638be69ab3561854f34b to before 447c9303942c439a117d9b76ce6d6e2116b38ee7Affected
LinuxLinux	4.6Affected before 4.6Not affected 5.10.270 through 5.10.Not affected 5.15.221 through 5.15.Not affected 6.1.188 through 6.1.Not affected 6.6.157 through 6.6.Not affected 6.12.109 through 6.12.Not affected 6.18.50 through 6.18.Not affected 7.2.4 through 7.2.*Not affected 7.3 and laterNot affected

Product

Versions

LinuxLinux

eaea34b23c46bf17b4a5638be69ab3561854f34b to before ad715e713610d2d5473c3a6498c825ccecf26491Affected
eaea34b23c46bf17b4a5638be69ab3561854f34b to before 708e87937de93f445225c134a2e20519f9b4ce60Affected
eaea34b23c46bf17b4a5638be69ab3561854f34b to before 18ef24cdb2eba32e38f1d27f2d02b7b4212e8f76Affected
eaea34b23c46bf17b4a5638be69ab3561854f34b to before 010eee265d6bd8769b6a523d2a0693d9b3f5df43Affected
eaea34b23c46bf17b4a5638be69ab3561854f34b to before 379d85c7f25f3e05a428225e6b8a65613c6e9b9dAffected
eaea34b23c46bf17b4a5638be69ab3561854f34b to before e098d9cc8859614a7f7baebc96e32a5a16b18ed2Affected
eaea34b23c46bf17b4a5638be69ab3561854f34b to before 0ada54ea63e48b9c1608e917ccb7dfadbe86db28Affected
eaea34b23c46bf17b4a5638be69ab3561854f34b to before 447c9303942c439a117d9b76ce6d6e2116b38ee7Affected

LinuxLinux

4.6Affected
before 4.6Not affected
5.10.270 through 5.10.*Not affected
5.15.221 through 5.15.*Not affected
6.1.188 through 6.1.*Not affected
6.6.157 through 6.6.*Not affected
6.12.109 through 6.12.*Not affected
6.18.50 through 6.18.*Not affected
7.2.4 through 7.2.*Not affected
7.3 and laterNot affected

References

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