CVE-2026-81000

Summary

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.

• CVE-2026-81000PoC

  Research repository for CVE-2026-81000 (TUNderflow), a Linux kernel TUN/TAP receive headroom integer underflow enabling local privilege escalation, with PoC, root-cause analysis, and lab setup.

• TUNderflowPoC

  Python PoC for CVE-2026-81000, a Linux kernel local privilege escalation via TUN/OVS out-of-bounds write and pipe_buffer flag manipulation to gain root.

• CVE-2026-81000PoC

  Educational CVE-2026-81000 proof-of-concept repository for authorized security research, vulnerability awareness, and controlled lab testing.