# CVE-2026-52940: linux: In the Linux kernel, the following vulnerability has been resolved: tun: zero the whole vnet header in tun_put_user(... CVE-2026-52940 is fixed in 20 products on 1 platform, first by DEBIAN-CVE-2026-52940, released June 28, 2026. It is not reported as exploited. Patch Radar priority: Routine. - Web page: https://patchblox.com/security/cve/CVE-2026-52940 - Priority: Routine - CVSS: 5.5 (medium) - EPSS: 0.0016 - CISA KEV: not listed - Exploited (vendor report): no - Publicly disclosed: no - Published: Jun 24, 2026 ## Description In the Linux kernel, the following vulnerability has been resolved: tun: zero the whole vnet header in tun_put_user() tun_put_user() declares an on-stack struct virtio_net_hdr_v1_hash_tunnel without zeroing it. For a non-tunnel skb, virtio_net_hdr_tnl_from_skb() only initializes the first 10 bytes (sizeof(struct virtio_net_hdr)), leaving bytes 10..23 (num_buffers and the hash/tunnel fields) as stack garbage. An unprivileged user can set the vnet header size to 24 with TUNSETVNETHDRSZ, so __tun_vnet_hdr_put() copies all 24 bytes of the partially-initialized struct to userspace, leaking 14 bytes of kernel stack on every read of a non-tunnel packet. Fix it the same way tun_get_user() already does by zeroing the whole header right after declaration. ## Where it's fixed | Platform | Product | Fixed in | Fix | Released | |---|---|---|---|---| | Linux | bpftool6.18 amzn 2023 | 1:6.18.36-69.134.amzn2023 | [ALAS2023-2026-1925](https://patchblox.com/security/data/fix/linux/alas2023-2026-1925.md) | Jul 6, 2026 | | Linux | bpftool6.18-debuginfo amzn 2023 | 1:6.18.36-69.134.amzn2023 | [ALAS2023-2026-1925](https://patchblox.com/security/data/fix/linux/alas2023-2026-1925.md) | Jul 6, 2026 | | Linux | kernel-livepatch-6.18.36-69.134 amzn 2023 | 1:1.0-0.amzn2023 | [ALAS2023-2026-1925](https://patchblox.com/security/data/fix/linux/alas2023-2026-1925.md) | Jul 6, 2026 | | Linux | kernel6.18 amzn 2023 | 1:6.18.36-69.134.amzn2023 | [ALAS2023-2026-1925](https://patchblox.com/security/data/fix/linux/alas2023-2026-1925.md) | Jul 6, 2026 | | Linux | kernel6.18-debuginfo amzn 2023 | 1:6.18.36-69.134.amzn2023 | [ALAS2023-2026-1925](https://patchblox.com/security/data/fix/linux/alas2023-2026-1925.md) | Jul 6, 2026 | | Linux | kernel6.18-debuginfo-common-aarch64 amzn 2023 | 1:6.18.36-69.134.amzn2023 | [ALAS2023-2026-1925](https://patchblox.com/security/data/fix/linux/alas2023-2026-1925.md) | Jul 6, 2026 | | Linux | kernel6.18-debuginfo-common-x86_64 amzn 2023 | 1:6.18.36-69.134.amzn2023 | [ALAS2023-2026-1925](https://patchblox.com/security/data/fix/linux/alas2023-2026-1925.md) | Jul 6, 2026 | | Linux | kernel6.18-devel amzn 2023 | 1:6.18.36-69.134.amzn2023 | [ALAS2023-2026-1925](https://patchblox.com/security/data/fix/linux/alas2023-2026-1925.md) | Jul 6, 2026 | | Linux | kernel6.18-headers amzn 2023 | 1:6.18.36-69.134.amzn2023 | [ALAS2023-2026-1925](https://patchblox.com/security/data/fix/linux/alas2023-2026-1925.md) | Jul 6, 2026 | | Linux | kernel6.18-modules-extra amzn 2023 | 1:6.18.36-69.134.amzn2023 | [ALAS2023-2026-1925](https://patchblox.com/security/data/fix/linux/alas2023-2026-1925.md) | Jul 6, 2026 | | Linux | kernel6.18-modules-extra-common amzn 2023 | 1:6.18.36-69.134.amzn2023 | [ALAS2023-2026-1925](https://patchblox.com/security/data/fix/linux/alas2023-2026-1925.md) | Jul 6, 2026 | | Linux | kernel6.18-tools amzn 2023 | 1:6.18.36-69.134.amzn2023 | [ALAS2023-2026-1925](https://patchblox.com/security/data/fix/linux/alas2023-2026-1925.md) | Jul 6, 2026 | | Linux | kernel6.18-tools-debuginfo amzn 2023 | 1:6.18.36-69.134.amzn2023 | [ALAS2023-2026-1925](https://patchblox.com/security/data/fix/linux/alas2023-2026-1925.md) | Jul 6, 2026 | | Linux | kernel6.18-tools-devel amzn 2023 | 1:6.18.36-69.134.amzn2023 | [ALAS2023-2026-1925](https://patchblox.com/security/data/fix/linux/alas2023-2026-1925.md) | Jul 6, 2026 | | Linux | linux Debian 14 | 7.0.13-1 | [DEBIAN-CVE-2026-52940](https://patchblox.com/security/data/fix/linux/debian-cve-2026-52940.md) | Jun 28, 2026 | | Linux | microvm-kernel6.18 amzn 2023 | 1:6.18.36-69.134.amzn2023 | [ALAS2023-2026-1925](https://patchblox.com/security/data/fix/linux/alas2023-2026-1925.md) | Jul 6, 2026 | | Linux | perf6.18 amzn 2023 | 1:6.18.36-69.134.amzn2023 | [ALAS2023-2026-1925](https://patchblox.com/security/data/fix/linux/alas2023-2026-1925.md) | Jul 6, 2026 | | Linux | perf6.18-debuginfo amzn 2023 | 1:6.18.36-69.134.amzn2023 | [ALAS2023-2026-1925](https://patchblox.com/security/data/fix/linux/alas2023-2026-1925.md) | Jul 6, 2026 | | Linux | python3-perf6.18 amzn 2023 | 1:6.18.36-69.134.amzn2023 | [ALAS2023-2026-1925](https://patchblox.com/security/data/fix/linux/alas2023-2026-1925.md) | Jul 6, 2026 | | Linux | python3-perf6.18-debuginfo amzn 2023 | 1:6.18.36-69.134.amzn2023 | [ALAS2023-2026-1925](https://patchblox.com/security/data/fix/linux/alas2023-2026-1925.md) | Jul 6, 2026 | --- Data as of 2026-11-08T19:12:23Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo Free to use with attribution: show "Data: Patchblox Patch Radar" with a link to https://patchblox.com/security/patch-radar. Terms, including what needs a written agreement: https://patchblox.com/security/patch-radar/use-the-data Product names, logos and trademarks shown on Patch Radar belong to their respective owners. They are used only to identify the software each security fix applies to and to help readers find their platform. Their use does not imply any affiliation with, or endorsement by, those owners, and Patchblox is not affiliated with any of them.