CVE-2026-81000 (CVSS 7.8)

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.

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CVSS v3.1 Score

7.8

HIGH

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

EPSS — Exploit Prediction

0.0016

Probability of exploitation

0.06%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

References

Other References

https://git.kernel.org/stable/c/010eee265d6bd8769b6a523d2a0693d9b3f5df43 https://git.kernel.org/stable/c/0ada54ea63e48b9c1608e917ccb7dfadbe86db28 https://git.kernel.org/stable/c/18ef24cdb2eba32e38f1d27f2d02b7b4212e8f76 https://git.kernel.org/stable/c/379d85c7f25f3e05a428225e6b8a65613c6e9b9d https://git.kernel.org/stable/c/447c9303942c439a117d9b76ce6d6e2116b38ee7 https://git.kernel.org/stable/c/708e87937de93f445225c134a2e20519f9b4ce60 https://git.kernel.org/stable/c/ad715e713610d2d5473c3a6498c825ccecf26491 https://git.kernel.org/stable/c/e098d9cc8859614a7f7baebc96e32a5a16b18ed2

Frequently Asked Questions

What is CVE-2026-81000? +

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. It has a CVSS v3.1 base score of 7.8 (HIGH).

How severe is CVE-2026-81000? +

CVE-2026-81000 has a CVSS v3.1 score of 7.8 out of 10, rated HIGH. This is a high-severity vulnerability that should be prioritized for patching. The EPSS score is 0.0016, placing it in the 0th percentile for exploitation probability.

How do I check if I'm vulnerable to CVE-2026-81000? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

CVE-2026-81000