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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.
Upstream advisory: https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-81000.mbox
A public local privilege escalation PoC for CVE-2026-81000 (TUNderflow) has been published. PoC: https://github.com/manizada/TUNderflow oss-security disclosure: https://seclists.org/oss-sec/2026/q3/822 Upstream fix: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=447c9303942c439a117d9b76ce6d6e2116b38ee7 Stable backports: 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 The published PoC demonstrates local user-to-root privilege escalation. Possible mitigation on systems that do not require TUN/TAP: echo "install tun /bin/true" > /etc/modprobe.d/disable-tun.conf Please re-evaluate the impact on supported RHEL kernels based on the published LPE PoC and upstream/stable fixes.
This issue has been addressed in the following products: Red Hat Enterprise Linux 8 Via RHSA-2026:71016 https://access.redhat.com/errata/RHSA-2026:71016
This issue has been addressed in the following products: Red Hat Enterprise Linux 8 Via RHSA-2026:71213 https://access.redhat.com/errata/RHSA-2026:71213
This issue has been addressed in the following products: Red Hat Enterprise Linux 10 Via RHSA-2026:71233 https://access.redhat.com/errata/RHSA-2026:71233
This issue has been addressed in the following products: Red Hat Enterprise Linux 9 Via RHSA-2026:71232 https://access.redhat.com/errata/RHSA-2026:71232
This issue has been addressed in the following products: Red Hat Enterprise Linux 8.4 Advanced Mission Critical Update Support Red Hat Enterprise Linux 8.4 Extended Update Support Long-Life Add-On Via RHSA-2026:71565 https://access.redhat.com/errata/RHSA-2026:71565
This issue has been addressed in the following products: Red Hat Enterprise Linux 8.6 Advanced Mission Critical Update Support Red Hat Enterprise Linux 8.6 Extended Update Support Long-Life Add-On Via RHSA-2026:71592 https://access.redhat.com/errata/RHSA-2026:71592
This issue has been addressed in the following products: Red Hat Enterprise Linux 8.8 Update Services for SAP Solutions Red Hat Enterprise Linux 8.8 Telecommunications Update Service Via RHSA-2026:71594 https://access.redhat.com/errata/RHSA-2026:71594
This issue has been addressed in the following products: Red Hat Enterprise Linux 9.2 Update Services for SAP Solutions Via RHSA-2026:71606 https://access.redhat.com/errata/RHSA-2026:71606
This issue has been addressed in the following products: Red Hat Enterprise Linux 9.4 Update Services for SAP Solutions Via RHSA-2026:71569 https://access.redhat.com/errata/RHSA-2026:71569
This issue has been addressed in the following products: Red Hat Enterprise Linux 9.2 Update Services for SAP Solutions Via RHSA-2026:71601 https://access.redhat.com/errata/RHSA-2026:71601
This issue has been addressed in the following products: Red Hat Enterprise Linux 10.0 Extended Update Support Via RHSA-2026:71599 https://access.redhat.com/errata/RHSA-2026:71599
This issue has been addressed in the following products: Red Hat Enterprise Linux 7 Extended Lifecycle Support Via RHSA-2026:71657 https://access.redhat.com/errata/RHSA-2026:71657
This issue has been addressed in the following products: Red Hat Enterprise Linux 9.6 Extended Update Support Via RHSA-2026:71631 https://access.redhat.com/errata/RHSA-2026:71631
This issue has been addressed in the following products: Red Hat Enterprise Linux 7 Extended Lifecycle Support Via RHSA-2026:71687 https://access.redhat.com/errata/RHSA-2026:71687