{"id":"CVE-2026-74496","state":"PUBLISHED","title":"fou: Fix use-after-free in fou_create()","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nfou: Fix use-after-free in fou_create()\n\nfou_create() publishes struct fou through sk_user_data before adding the\nnew FOU port to the per-netns list.  If fou_add_to_port_list() fails,\nthe error path frees fou while it is still reachable through\nsk_user_data.  A concurrent receive can then dereference the freed\nobject in fou_from_sock().\n\nThis ordering issue was previously noted in the linked discussion.\n\nThe failure is reachable when local port 0 is requested.  Each socket\nbinds to a different ephemeral port, but fou_cfg_cmp() compares the\nrequested port 0 and reports -EALREADY once an entry already exists.\n\nRelease the tunnel socket before freeing fou so sk_user_data is cleared\nfirst, and defer reclamation with kfree_rcu() to protect concurrent RCU\nreaders.  This matches the lifetime handling in fou_release().","publishedAt":"2026-08-15T12:27:23.854Z","updatedAt":"2026-10-16T19:05:50.395Z","severity":{"score":7.8,"label":"High","version":"3.1","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","source":"Linux"},"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"23461551c00628c3f3fe9cf837bf53cf8f212b63","status":"affected","lessThan":"0ee628a58d83e571f36ec9f07624d6845e420c50","versionType":"git"},{"version":"23461551c00628c3f3fe9cf837bf53cf8f212b63","status":"affected","lessThan":"a6fca682cfa2041e31aa72cc397c4a1406eb7468","versionType":"git"},{"version":"23461551c00628c3f3fe9cf837bf53cf8f212b63","status":"affected","lessThan":"b3f9c3e60aa25453774f899d25b5e61dd0bec1d5","versionType":"git"},{"version":"23461551c00628c3f3fe9cf837bf53cf8f212b63","status":"affected","lessThan":"99f4d3120b244f92e5df787152041296a2860cb5","versionType":"git"},{"version":"23461551c00628c3f3fe9cf837bf53cf8f212b63","status":"affected","lessThan":"58835985c035a8333742f829ad7e0889a082f9d3","versionType":"git"},{"version":"23461551c00628c3f3fe9cf837bf53cf8f212b63","status":"affected","lessThan":"9042867d4701728f0c6527215b11471759904d8f","versionType":"git"},{"version":"23461551c00628c3f3fe9cf837bf53cf8f212b63","status":"affected","lessThan":"a28d8903bfe76089ea4bbdbff9976965f9ef8107","versionType":"git"},{"version":"23461551c00628c3f3fe9cf837bf53cf8f212b63","status":"affected","lessThan":"b14361aca6350ff7907b0e9903c7b94dc7d5d4a0","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":"5.10.271","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.222","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.189","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.158","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.111","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.53","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.1.8","status":"unaffected","lessThanOrEqual":"7.1.*","versionType":"semver"},{"version":"7.2","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/0ee628a58d83e571f36ec9f07624d6845e420c50","https://git.kernel.org/stable/c/a6fca682cfa2041e31aa72cc397c4a1406eb7468","https://git.kernel.org/stable/c/b3f9c3e60aa25453774f899d25b5e61dd0bec1d5","https://git.kernel.org/stable/c/99f4d3120b244f92e5df787152041296a2860cb5","https://git.kernel.org/stable/c/58835985c035a8333742f829ad7e0889a082f9d3","https://git.kernel.org/stable/c/9042867d4701728f0c6527215b11471759904d8f","https://git.kernel.org/stable/c/a28d8903bfe76089ea4bbdbff9976965f9ef8107","https://git.kernel.org/stable/c/b14361aca6350ff7907b0e9903c7b94dc7d5d4a0"],"weaknesses":[],"ingestedAt":"2026-10-29T20:12:58.252Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/74xxx/CVE-2026-74496.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-74496","state":"PUBLISHED","datePublished":"2026-08-15T12:27:23.854Z","dateUpdated":"2026-10-16T19:05:50.395Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-08-15T05:44:03.906Z"},"containers":{"cna":{"title":"fou: Fix use-after-free in fou_create()","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nfou: Fix use-after-free in fou_create()\n\nfou_create() publishes struct fou through sk_user_data before adding the\nnew FOU port to the per-netns list.  If fou_add_to_port_list() fails,\nthe error path frees fou while it is still reachable through\nsk_user_data.  A concurrent receive can then dereference the freed\nobject in fou_from_sock().\n\nThis ordering issue was previously noted in the linked discussion.\n\nThe failure is reachable when local port 0 is requested.  Each socket\nbinds to a different ephemeral port, but fou_cfg_cmp() compares the\nrequested port 0 and reports -EALREADY once an entry already exists.\n\nRelease the tunnel socket before freeing fou so sk_user_data is cleared\nfirst, and defer reclamation with kfree_rcu() to protect concurrent RCU\nreaders.  This matches the lifetime handling in fou_release()."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"23461551c00628c3f3fe9cf837bf53cf8f212b63","status":"affected","lessThan":"0ee628a58d83e571f36ec9f07624d6845e420c50","versionType":"git"},{"version":"23461551c00628c3f3fe9cf837bf53cf8f212b63","status":"affected","lessThan":"a6fca682cfa2041e31aa72cc397c4a1406eb7468","versionType":"git"},{"version":"23461551c00628c3f3fe9cf837bf53cf8f212b63","status":"affected","lessThan":"b3f9c3e60aa25453774f899d25b5e61dd0bec1d5","versionType":"git"},{"version":"23461551c00628c3f3fe9cf837bf53cf8f212b63","status":"affected","lessThan":"99f4d3120b244f92e5df787152041296a2860cb5","versionType":"git"},{"version":"23461551c00628c3f3fe9cf837bf53cf8f212b63","status":"affected","lessThan":"58835985c035a8333742f829ad7e0889a082f9d3","versionType":"git"},{"version":"23461551c00628c3f3fe9cf837bf53cf8f212b63","status":"affected","lessThan":"9042867d4701728f0c6527215b11471759904d8f","versionType":"git"},{"version":"23461551c00628c3f3fe9cf837bf53cf8f212b63","status":"affected","lessThan":"a28d8903bfe76089ea4bbdbff9976965f9ef8107","versionType":"git"},{"version":"23461551c00628c3f3fe9cf837bf53cf8f212b63","status":"affected","lessThan":"b14361aca6350ff7907b0e9903c7b94dc7d5d4a0","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":"5.10.271","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.222","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.189","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.158","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.111","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.53","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.1.8","status":"unaffected","lessThanOrEqual":"7.1.*","versionType":"semver"},{"version":"7.2","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/0ee628a58d83e571f36ec9f07624d6845e420c50"},{"url":"https://git.kernel.org/stable/c/a6fca682cfa2041e31aa72cc397c4a1406eb7468"},{"url":"https://git.kernel.org/stable/c/b3f9c3e60aa25453774f899d25b5e61dd0bec1d5"},{"url":"https://git.kernel.org/stable/c/99f4d3120b244f92e5df787152041296a2860cb5"},{"url":"https://git.kernel.org/stable/c/58835985c035a8333742f829ad7e0889a082f9d3"},{"url":"https://git.kernel.org/stable/c/9042867d4701728f0c6527215b11471759904d8f"},{"url":"https://git.kernel.org/stable/c/a28d8903bfe76089ea4bbdbff9976965f9ef8107"},{"url":"https://git.kernel.org/stable/c/b14361aca6350ff7907b0e9903c7b94dc7d5d4a0"}],"metrics":[{"cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","baseScore":7.8,"baseSeverity":"HIGH"},"scenarios":[{"lang":"en","value":"AV:L - The UAF is opened only via local FOU_CMD_ADD genetlink into fou_create(); remote UDP can race the dangling sk_user_data read in fou_udp_recv/gue_udp_recv but cannot alone reach the erroneous teardown path.\nAC:L - An attacker with CAP_NET_ADMIN controls both sides: issue a second FOU_CMD_ADD with port 0 to force -EALREADY on fou_add_to_port_list while concurrently sending UDP/GRO traffic to the just-bound ephemeral socket during the kfree window.\nPR:L - FOU_CMD_ADD is gated by GENL_ADMIN_PERM (CAP_NET_ADMIN); the fou genl family is netnsok, so a user with CAP_NET_ADMIN inside unshare -Urn can configure FOU and trigger the failing add path without init-namespace root.\nUI:N - Exploitation is fully programmatic via concurrent netlink FOU_CMD_ADD requests and attacker-controlled UDP packets; no victim mount, file open, or other interactive action is required.\nS:U - Impact is kernel heap corruption and privilege escalation within the same security authority; this is not a VM escape, IOMMU bypass, or other cross-boundary scope change.\nC:H - Concurrent readers call fou_from_sock() and dereference freed struct fou fields (family, protocol, flags); reclaimed slab contents give attacker-controlled reads and kernel pointer disclosure primitives typical of UAF.\nI:H - Freed struct fou is attacker-reclaimable kmalloc memory; fou_gro_receive indexes inet_offloads[fou->protocol] from the dangling pointer, enabling heap grooming for arbitrary writes and control-flow hijack.\nA:H - Use-after-free in UDP receive/GRO softirq reliably causes KASAN violations and, on production kernels, invalid pointer dereferences or panics when accessing the freed fou object during packet processing."}]}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-10-03T10:56:03.355Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.18","versionEndExcluding":"5.10.271"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.18","versionEndExcluding":"5.15.222"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.18","versionEndExcluding":"6.1.189"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.18","versionEndExcluding":"6.6.158"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.18","versionEndExcluding":"6.12.111"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.18","versionEndExcluding":"6.18.53"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.18","versionEndExcluding":"7.1.8"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.18","versionEndExcluding":"7.2"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"id":"CVE-2026-74496","role":"CISA Coordinator","options":[{"Exploitation":"none"},{"Automatable":"no"},{"Technical Impact":"total"}],"version":"2.0.3","timestamp":"2026-10-16T18:58:18.343359Z"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-10-16T19:05:50.395Z"}}]}}}