{"id":"CVE-2026-52940","state":"PUBLISHED","title":"tun: zero the whole vnet header in tun_put_user()","description":"In the Linux kernel, the following vulnerability has been resolved:\n\ntun: zero the whole vnet header in tun_put_user()\n\ntun_put_user() declares an on-stack struct virtio_net_hdr_v1_hash_tunnel\nwithout zeroing it. For a non-tunnel skb, virtio_net_hdr_tnl_from_skb()\nonly initializes the first 10 bytes (sizeof(struct virtio_net_hdr)),\nleaving bytes 10..23 (num_buffers and the hash/tunnel fields) as stack\ngarbage.\n\nAn unprivileged user can set the vnet header size to 24 with\nTUNSETVNETHDRSZ, so __tun_vnet_hdr_put() copies all 24 bytes of the\npartially-initialized struct to userspace, leaking 14 bytes of kernel\nstack on every read of a non-tunnel packet.\n\nFix it the same way tun_get_user() already does by zeroing the whole\nheader right after declaration.","publishedAt":"2026-06-24T07:14:29.281Z","updatedAt":"2026-06-24T07:14:29.281Z","severity":null,"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"288f30435132d2f9e7a29ec9b9745a4f9dc7fd37","status":"affected","lessThan":"5fd1fa5a4254bfdd70571c77f5e3bcb4e43738d5","versionType":"git"},{"version":"288f30435132d2f9e7a29ec9b9745a4f9dc7fd37","status":"affected","lessThan":"585cb85e9a29185be05f326369573c2663cf4380","versionType":"git"},{"version":"288f30435132d2f9e7a29ec9b9745a4f9dc7fd37","status":"affected","lessThan":"7f2fcff15e99bb852f6967396ed12b38376e2c8d","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["drivers/net/tun.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"6.17","status":"affected"},{"version":"0","status":"unaffected","lessThan":"6.17","versionType":"semver"},{"version":"6.18.36","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.0.13","status":"unaffected","lessThanOrEqual":"7.0.*","versionType":"semver"},{"version":"7.1","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["drivers/net/tun.c"]}],"references":["https://git.kernel.org/stable/c/5fd1fa5a4254bfdd70571c77f5e3bcb4e43738d5","https://git.kernel.org/stable/c/585cb85e9a29185be05f326369573c2663cf4380","https://git.kernel.org/stable/c/7f2fcff15e99bb852f6967396ed12b38376e2c8d"],"weaknesses":[],"ingestedAt":"2026-10-29T20:12:16.098Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/52xxx/CVE-2026-52940.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-52940","state":"PUBLISHED","datePublished":"2026-06-24T07:14:29.281Z","dateUpdated":"2026-06-24T07:14:29.281Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-06-09T07:44:35.370Z"},"containers":{"cna":{"title":"tun: zero the whole vnet header in tun_put_user()","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\ntun: zero the whole vnet header in tun_put_user()\n\ntun_put_user() declares an on-stack struct virtio_net_hdr_v1_hash_tunnel\nwithout zeroing it. For a non-tunnel skb, virtio_net_hdr_tnl_from_skb()\nonly initializes the first 10 bytes (sizeof(struct virtio_net_hdr)),\nleaving bytes 10..23 (num_buffers and the hash/tunnel fields) as stack\ngarbage.\n\nAn unprivileged user can set the vnet header size to 24 with\nTUNSETVNETHDRSZ, so __tun_vnet_hdr_put() copies all 24 bytes of the\npartially-initialized struct to userspace, leaking 14 bytes of kernel\nstack on every read of a non-tunnel packet.\n\nFix it the same way tun_get_user() already does by zeroing the whole\nheader right after declaration."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"288f30435132d2f9e7a29ec9b9745a4f9dc7fd37","status":"affected","lessThan":"5fd1fa5a4254bfdd70571c77f5e3bcb4e43738d5","versionType":"git"},{"version":"288f30435132d2f9e7a29ec9b9745a4f9dc7fd37","status":"affected","lessThan":"585cb85e9a29185be05f326369573c2663cf4380","versionType":"git"},{"version":"288f30435132d2f9e7a29ec9b9745a4f9dc7fd37","status":"affected","lessThan":"7f2fcff15e99bb852f6967396ed12b38376e2c8d","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["drivers/net/tun.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"6.17","status":"affected"},{"version":"0","status":"unaffected","lessThan":"6.17","versionType":"semver"},{"version":"6.18.36","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.0.13","status":"unaffected","lessThanOrEqual":"7.0.*","versionType":"semver"},{"version":"7.1","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["drivers/net/tun.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/5fd1fa5a4254bfdd70571c77f5e3bcb4e43738d5"},{"url":"https://git.kernel.org/stable/c/585cb85e9a29185be05f326369573c2663cf4380"},{"url":"https://git.kernel.org/stable/c/7f2fcff15e99bb852f6967396ed12b38376e2c8d"}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-06-24T07:14:29.281Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.17","versionEndExcluding":"6.18.36"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.17","versionEndExcluding":"7.0.13"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.17","versionEndExcluding":"7.1"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}}}}}