{"id":"CVE-2026-23095","state":"PUBLISHED","title":"gue: Fix skb memleak with inner IP protocol 0.","description":"In the Linux kernel, the following vulnerability has been resolved:\n\ngue: Fix skb memleak with inner IP protocol 0.\n\nsyzbot reported skb memleak below. [0]\n\nThe repro generated a GUE packet with its inner protocol 0.\n\ngue_udp_recv() returns -guehdr->proto_ctype for \"resubmit\"\nin ip_protocol_deliver_rcu(), but this only works with\nnon-zero protocol number.\n\nLet's drop such packets.\n\nNote that 0 is a valid number (IPv6 Hop-by-Hop Option).\n\nI think it is not practical to encap HOPOPT in GUE, so once\nsomeone starts to complain, we could pass down a resubmit\nflag pointer to distinguish two zeros from the upper layer:\n\n  * no error\n  * resubmit HOPOPT\n\n[0]\nBUG: memory leak\nunreferenced object 0xffff888109695a00 (size 240):\n  comm \"syz.0.17\", pid 6088, jiffies 4294943096\n  hex dump (first 32 bytes):\n    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................\n    00 40 c2 10 81 88 ff ff 00 00 00 00 00 00 00 00  .@..............\n  backtrace (crc a84b336f):\n    kmemleak_alloc_recursive include/linux/kmemleak.h:44 [inline]\n    slab_post_alloc_hook mm/slub.c:4958 [inline]\n    slab_alloc_node mm/slub.c:5263 [inline]\n    kmem_cache_alloc_noprof+0x3b4/0x590 mm/slub.c:5270\n    __build_skb+0x23/0x60 net/core/skbuff.c:474\n    build_skb+0x20/0x190 net/core/skbuff.c:490\n    __tun_build_skb drivers/net/tun.c:1541 [inline]\n    tun_build_skb+0x4a1/0xa40 drivers/net/tun.c:1636\n    tun_get_user+0xc12/0x2030 drivers/net/tun.c:1770\n    tun_chr_write_iter+0x71/0x120 drivers/net/tun.c:1999\n    new_sync_write fs/read_write.c:593 [inline]\n    vfs_write+0x45d/0x710 fs/read_write.c:686\n    ksys_write+0xa7/0x170 fs/read_write.c:738\n    do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]\n    do_syscall_64+0xa4/0xf80 arch/x86/entry/syscall_64.c:94\n    entry_SYSCALL_64_after_hwframe+0x77/0x7f","publishedAt":"2026-02-04T16:08:17.990Z","updatedAt":"2026-10-19T18:25:30.509Z","severity":{"score":7.5,"label":"High","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","source":"Linux"},"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"37dd0247797b168ad1cc7f5dbec825a1ee66535b","status":"affected","lessThan":"886f186328b718400dbf79e1bc8cbcbd710ab766","versionType":"git"},{"version":"37dd0247797b168ad1cc7f5dbec825a1ee66535b","status":"affected","lessThan":"380a82d36e37db49fd41ecc378c22fd29392e96a","versionType":"git"},{"version":"37dd0247797b168ad1cc7f5dbec825a1ee66535b","status":"affected","lessThan":"536f5bbc322eb1e175bdd1ced22b236a951c4d8f","versionType":"git"},{"version":"37dd0247797b168ad1cc7f5dbec825a1ee66535b","status":"affected","lessThan":"f87b9b7a618c82e7465e872eb10e14c803871892","versionType":"git"},{"version":"37dd0247797b168ad1cc7f5dbec825a1ee66535b","status":"affected","lessThan":"ce569b389a5c78d64788a5ea94560e17fa574b35","versionType":"git"},{"version":"37dd0247797b168ad1cc7f5dbec825a1ee66535b","status":"affected","lessThan":"5437a279804ced8088cabb945dba88a26d828f8c","versionType":"git"},{"version":"37dd0247797b168ad1cc7f5dbec825a1ee66535b","status":"affected","lessThan":"9a56796ad258786d3624eef5aefba394fc9bdded","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/ipv4/fou_core.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"3.18","status":"affected"},{"version":"0","status":"unaffected","lessThan":"3.18","versionType":"semver"},{"version":"5.10.249","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.199","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.162","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.122","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.68","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.8","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"6.19","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/ipv4/fou_core.c"]}],"references":["https://git.kernel.org/stable/c/886f186328b718400dbf79e1bc8cbcbd710ab766","https://git.kernel.org/stable/c/380a82d36e37db49fd41ecc378c22fd29392e96a","https://git.kernel.org/stable/c/536f5bbc322eb1e175bdd1ced22b236a951c4d8f","https://git.kernel.org/stable/c/f87b9b7a618c82e7465e872eb10e14c803871892","https://git.kernel.org/stable/c/ce569b389a5c78d64788a5ea94560e17fa574b35","https://git.kernel.org/stable/c/5437a279804ced8088cabb945dba88a26d828f8c","https://git.kernel.org/stable/c/9a56796ad258786d3624eef5aefba394fc9bdded","https://cert-portal.siemens.com/productcert/html/ssa-019113.html","https://cert-portal.siemens.com/productcert/html/ssa-457936.html"],"weaknesses":["CWE-401"],"ingestedAt":"2026-10-29T20:11:21.040Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/23xxx/CVE-2026-23095.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-23095","state":"PUBLISHED","datePublished":"2026-02-04T16:08:17.990Z","dateUpdated":"2026-10-19T18:25:30.509Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-01-13T15:37:45.963Z"},"containers":{"cna":{"title":"gue: Fix skb memleak with inner IP protocol 0.","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\ngue: Fix skb memleak with inner IP protocol 0.\n\nsyzbot reported skb memleak below. [0]\n\nThe repro generated a GUE packet with its inner protocol 0.\n\ngue_udp_recv() returns -guehdr->proto_ctype for \"resubmit\"\nin ip_protocol_deliver_rcu(), but this only works with\nnon-zero protocol number.\n\nLet's drop such packets.\n\nNote that 0 is a valid number (IPv6 Hop-by-Hop Option).\n\nI think it is not practical to encap HOPOPT in GUE, so once\nsomeone starts to complain, we could pass down a resubmit\nflag pointer to distinguish two zeros from the upper layer:\n\n  * no error\n  * resubmit HOPOPT\n\n[0]\nBUG: memory leak\nunreferenced object 0xffff888109695a00 (size 240):\n  comm \"syz.0.17\", pid 6088, jiffies 4294943096\n  hex dump (first 32 bytes):\n    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................\n    00 40 c2 10 81 88 ff ff 00 00 00 00 00 00 00 00  .@..............\n  backtrace (crc a84b336f):\n    kmemleak_alloc_recursive include/linux/kmemleak.h:44 [inline]\n    slab_post_alloc_hook mm/slub.c:4958 [inline]\n    slab_alloc_node mm/slub.c:5263 [inline]\n    kmem_cache_alloc_noprof+0x3b4/0x590 mm/slub.c:5270\n    __build_skb+0x23/0x60 net/core/skbuff.c:474\n    build_skb+0x20/0x190 net/core/skbuff.c:490\n    __tun_build_skb drivers/net/tun.c:1541 [inline]\n    tun_build_skb+0x4a1/0xa40 drivers/net/tun.c:1636\n    tun_get_user+0xc12/0x2030 drivers/net/tun.c:1770\n    tun_chr_write_iter+0x71/0x120 drivers/net/tun.c:1999\n    new_sync_write fs/read_write.c:593 [inline]\n    vfs_write+0x45d/0x710 fs/read_write.c:686\n    ksys_write+0xa7/0x170 fs/read_write.c:738\n    do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]\n    do_syscall_64+0xa4/0xf80 arch/x86/entry/syscall_64.c:94\n    entry_SYSCALL_64_after_hwframe+0x77/0x7f"}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"37dd0247797b168ad1cc7f5dbec825a1ee66535b","status":"affected","lessThan":"886f186328b718400dbf79e1bc8cbcbd710ab766","versionType":"git"},{"version":"37dd0247797b168ad1cc7f5dbec825a1ee66535b","status":"affected","lessThan":"380a82d36e37db49fd41ecc378c22fd29392e96a","versionType":"git"},{"version":"37dd0247797b168ad1cc7f5dbec825a1ee66535b","status":"affected","lessThan":"536f5bbc322eb1e175bdd1ced22b236a951c4d8f","versionType":"git"},{"version":"37dd0247797b168ad1cc7f5dbec825a1ee66535b","status":"affected","lessThan":"f87b9b7a618c82e7465e872eb10e14c803871892","versionType":"git"},{"version":"37dd0247797b168ad1cc7f5dbec825a1ee66535b","status":"affected","lessThan":"ce569b389a5c78d64788a5ea94560e17fa574b35","versionType":"git"},{"version":"37dd0247797b168ad1cc7f5dbec825a1ee66535b","status":"affected","lessThan":"5437a279804ced8088cabb945dba88a26d828f8c","versionType":"git"},{"version":"37dd0247797b168ad1cc7f5dbec825a1ee66535b","status":"affected","lessThan":"9a56796ad258786d3624eef5aefba394fc9bdded","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/ipv4/fou_core.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"3.18","status":"affected"},{"version":"0","status":"unaffected","lessThan":"3.18","versionType":"semver"},{"version":"5.10.249","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.199","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.162","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.122","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.68","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.8","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"6.19","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/ipv4/fou_core.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/886f186328b718400dbf79e1bc8cbcbd710ab766"},{"url":"https://git.kernel.org/stable/c/380a82d36e37db49fd41ecc378c22fd29392e96a"},{"url":"https://git.kernel.org/stable/c/536f5bbc322eb1e175bdd1ced22b236a951c4d8f"},{"url":"https://git.kernel.org/stable/c/f87b9b7a618c82e7465e872eb10e14c803871892"},{"url":"https://git.kernel.org/stable/c/ce569b389a5c78d64788a5ea94560e17fa574b35"},{"url":"https://git.kernel.org/stable/c/5437a279804ced8088cabb945dba88a26d828f8c"},{"url":"https://git.kernel.org/stable/c/9a56796ad258786d3624eef5aefba394fc9bdded"}],"metrics":[{"cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","baseScore":7.5,"baseSeverity":"HIGH"},"scenarios":[{"lang":"en","value":"AV:N - GUE processes incoming UDP packets from the network. Once a GUE tunnel is configured (its intended purpose in datacenter/cloud deployments), any remote attacker can send crafted UDP packets to the GUE port to trigger the leak.\nAC:L - The attacker simply sends a UDP packet with a GUE header containing proto_ctype=0. No race conditions, no special timing, and no conditions beyond the attacker's control once the GUE tunnel endpoint exists.\nPR:N - No authentication or privileges are needed to send UDP packets to a GUE tunnel endpoint. The vulnerability is in the packet receive path which processes all incoming packets without any authentication gate.\nUI:N - No user interaction is required. The vulnerability is triggered purely by receiving a crafted network packet.\nS:U - The vulnerability affects kernel memory within the same security authority. No scope boundary (VM, sandbox, IOMMU) is crossed.\nC:N - This is a pure memory leak — the skb is not freed but no memory contents are disclosed to the attacker. There is no information disclosure path.\nI:N - This is a memory leak, not a memory corruption. No kernel data structures are modified or corrupted; the skb simply becomes unreachable and is never freed.\nA:H - The attacker can repeatedly send crafted GUE packets over the network at high rate, each leaking ~240 bytes of kernel memory. 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