{"id":"CVE-2025-68227","state":"PUBLISHED","title":"mptcp: Fix proto fallback detection with BPF","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nmptcp: Fix proto fallback detection with BPF\n\nThe sockmap feature allows bpf syscall from userspace, or based\non bpf sockops, replacing the sk_prot of sockets during protocol stack\nprocessing with sockmap's custom read/write interfaces.\n'''\ntcp_rcv_state_process()\n  syn_recv_sock()/subflow_syn_recv_sock()\n    tcp_init_transfer(BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB)\n      bpf_skops_established       <== sockops\n        bpf_sock_map_update(sk)   <== call bpf helper\n          tcp_bpf_update_proto()  <== update sk_prot\n'''\n\nWhen the server has MPTCP enabled but the client sends a TCP SYN\nwithout MPTCP, subflow_syn_recv_sock() performs a fallback on the\nsubflow, replacing the subflow sk's sk_prot with the native sk_prot.\n'''\nsubflow_syn_recv_sock()\n  subflow_ulp_fallback()\n    subflow_drop_ctx()\n      mptcp_subflow_ops_undo_override()\n'''\n\nThen, this subflow can be normally used by sockmap, which replaces the\nnative sk_prot with sockmap's custom sk_prot. The issue occurs when the\nuser executes accept::mptcp_stream_accept::mptcp_fallback_tcp_ops().\nHere, it uses sk->sk_prot to compare with the native sk_prot, but this\nis incorrect when sockmap is used, as we may incorrectly set\nsk->sk_socket->ops.\n\nThis fix uses the more generic sk_family for the comparison instead.\n\nAdditionally, this also prevents a WARNING from occurring:\n\nresult from ./scripts/decode_stacktrace.sh:\n------------[ cut here ]------------\nWARNING: CPU: 0 PID: 337 at net/mptcp/protocol.c:68 mptcp_stream_accept \\\n(net/mptcp/protocol.c:4005)\nModules linked in:\n...\n\nPKRU: 55555554\nCall Trace:\n<TASK>\ndo_accept (net/socket.c:1989)\n__sys_accept4 (net/socket.c:2028 net/socket.c:2057)\n__x64_sys_accept (net/socket.c:2067)\nx64_sys_call (arch/x86/entry/syscall_64.c:41)\ndo_syscall_64 (arch/x86/entry/syscall_64.c:63 arch/x86/entry/syscall_64.c:94)\nentry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130)\nRIP: 0033:0x7f87ac92b83d\n\n---[ end trace 0000000000000000 ]---","publishedAt":"2025-12-16T13:57:20.027Z","updatedAt":"2026-05-11T21:49:17.263Z","severity":null,"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"0b4f33def7bbde1ce2fea05f116639270e7acdc7","status":"affected","lessThan":"92c4092fe012ecdfa5fb05d394f1c1d8f91ad81c","versionType":"git"},{"version":"0b4f33def7bbde1ce2fea05f116639270e7acdc7","status":"affected","lessThan":"7ee8f015eb47907745e2070184a8ab1e442ac3c4","versionType":"git"},{"version":"0b4f33def7bbde1ce2fea05f116639270e7acdc7","status":"affected","lessThan":"344974ea1a3ca30e4920687b0091bda4438cebdb","versionType":"git"},{"version":"0b4f33def7bbde1ce2fea05f116639270e7acdc7","status":"affected","lessThan":"037cc50589643342d69185b663ecf9d26cce91e8","versionType":"git"},{"version":"0b4f33def7bbde1ce2fea05f116639270e7acdc7","status":"affected","lessThan":"9b1980b6f23fa30bf12add19f37c7458625099eb","versionType":"git"},{"version":"0b4f33def7bbde1ce2fea05f116639270e7acdc7","status":"affected","lessThan":"1a0d5c74af9b6ba9ffdf1172de5a1a6df5922a00","versionType":"git"},{"version":"0b4f33def7bbde1ce2fea05f116639270e7acdc7","status":"affected","lessThan":"c77b3b79a92e3345aa1ee296180d1af4e7031f8f","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/mptcp/protocol.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"5.7","status":"affected"},{"version":"0","status":"unaffected","lessThan":"5.7","versionType":"semver"},{"version":"5.10.247","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.197","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.159","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.118","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.60","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.17.10","status":"unaffected","lessThanOrEqual":"6.17.*","versionType":"semver"},{"version":"6.18","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/mptcp/protocol.c"]}],"references":["https://git.kernel.org/stable/c/92c4092fe012ecdfa5fb05d394f1c1d8f91ad81c","https://git.kernel.org/stable/c/7ee8f015eb47907745e2070184a8ab1e442ac3c4","https://git.kernel.org/stable/c/344974ea1a3ca30e4920687b0091bda4438cebdb","https://git.kernel.org/stable/c/037cc50589643342d69185b663ecf9d26cce91e8","https://git.kernel.org/stable/c/9b1980b6f23fa30bf12add19f37c7458625099eb","https://git.kernel.org/stable/c/1a0d5c74af9b6ba9ffdf1172de5a1a6df5922a00","https://git.kernel.org/stable/c/c77b3b79a92e3345aa1ee296180d1af4e7031f8f"],"weaknesses":[],"ingestedAt":"2026-10-29T20:09:56.034Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2025/68xxx/CVE-2025-68227.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2025-68227","state":"PUBLISHED","datePublished":"2025-12-16T13:57:20.027Z","dateUpdated":"2026-05-11T21:49:17.263Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2025-12-16T13:41:40.257Z"},"containers":{"cna":{"title":"mptcp: Fix proto fallback detection with BPF","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nmptcp: Fix proto fallback detection with BPF\n\nThe sockmap feature allows bpf syscall from userspace, or based\non bpf sockops, replacing the sk_prot of sockets during protocol stack\nprocessing with sockmap's custom read/write interfaces.\n'''\ntcp_rcv_state_process()\n  syn_recv_sock()/subflow_syn_recv_sock()\n    tcp_init_transfer(BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB)\n      bpf_skops_established       <== sockops\n        bpf_sock_map_update(sk)   <== call bpf helper\n          tcp_bpf_update_proto()  <== update sk_prot\n'''\n\nWhen the server has MPTCP enabled but the client sends a TCP SYN\nwithout MPTCP, subflow_syn_recv_sock() performs a fallback on the\nsubflow, replacing the subflow sk's sk_prot with the native sk_prot.\n'''\nsubflow_syn_recv_sock()\n  subflow_ulp_fallback()\n    subflow_drop_ctx()\n      mptcp_subflow_ops_undo_override()\n'''\n\nThen, this subflow can be normally used by sockmap, which replaces the\nnative sk_prot with sockmap's custom sk_prot. The issue occurs when the\nuser executes accept::mptcp_stream_accept::mptcp_fallback_tcp_ops().\nHere, it uses sk->sk_prot to compare with the native sk_prot, but this\nis incorrect when sockmap is used, as we may incorrectly set\nsk->sk_socket->ops.\n\nThis fix uses the more generic sk_family for the comparison instead.\n\nAdditionally, this also prevents a WARNING from occurring:\n\nresult from ./scripts/decode_stacktrace.sh:\n------------[ cut here ]------------\nWARNING: CPU: 0 PID: 337 at net/mptcp/protocol.c:68 mptcp_stream_accept \\\n(net/mptcp/protocol.c:4005)\nModules linked in:\n...\n\nPKRU: 55555554\nCall Trace:\n<TASK>\ndo_accept (net/socket.c:1989)\n__sys_accept4 (net/socket.c:2028 net/socket.c:2057)\n__x64_sys_accept (net/socket.c:2067)\nx64_sys_call (arch/x86/entry/syscall_64.c:41)\ndo_syscall_64 (arch/x86/entry/syscall_64.c:63 arch/x86/entry/syscall_64.c:94)\nentry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130)\nRIP: 0033:0x7f87ac92b83d\n\n---[ end trace 0000000000000000 ]---"}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"0b4f33def7bbde1ce2fea05f116639270e7acdc7","status":"affected","lessThan":"92c4092fe012ecdfa5fb05d394f1c1d8f91ad81c","versionType":"git"},{"version":"0b4f33def7bbde1ce2fea05f116639270e7acdc7","status":"affected","lessThan":"7ee8f015eb47907745e2070184a8ab1e442ac3c4","versionType":"git"},{"version":"0b4f33def7bbde1ce2fea05f116639270e7acdc7","status":"affected","lessThan":"344974ea1a3ca30e4920687b0091bda4438cebdb","versionType":"git"},{"version":"0b4f33def7bbde1ce2fea05f116639270e7acdc7","status":"affected","lessThan":"037cc50589643342d69185b663ecf9d26cce91e8","versionType":"git"},{"version":"0b4f33def7bbde1ce2fea05f116639270e7acdc7","status":"affected","lessThan":"9b1980b6f23fa30bf12add19f37c7458625099eb","versionType":"git"},{"version":"0b4f33def7bbde1ce2fea05f116639270e7acdc7","status":"affected","lessThan":"1a0d5c74af9b6ba9ffdf1172de5a1a6df5922a00","versionType":"git"},{"version":"0b4f33def7bbde1ce2fea05f116639270e7acdc7","status":"affected","lessThan":"c77b3b79a92e3345aa1ee296180d1af4e7031f8f","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/mptcp/protocol.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"5.7","status":"affected"},{"version":"0","status":"unaffected","lessThan":"5.7","versionType":"semver"},{"version":"5.10.247","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.197","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.159","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.118","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.60","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.17.10","status":"unaffected","lessThanOrEqual":"6.17.*","versionType":"semver"},{"version":"6.18","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/mptcp/protocol.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/92c4092fe012ecdfa5fb05d394f1c1d8f91ad81c"},{"url":"https://git.kernel.org/stable/c/7ee8f015eb47907745e2070184a8ab1e442ac3c4"},{"url":"https://git.kernel.org/stable/c/344974ea1a3ca30e4920687b0091bda4438cebdb"},{"url":"https://git.kernel.org/stable/c/037cc50589643342d69185b663ecf9d26cce91e8"},{"url":"https://git.kernel.org/stable/c/9b1980b6f23fa30bf12add19f37c7458625099eb"},{"url":"https://git.kernel.org/stable/c/1a0d5c74af9b6ba9ffdf1172de5a1a6df5922a00"},{"url":"https://git.kernel.org/stable/c/c77b3b79a92e3345aa1ee296180d1af4e7031f8f"}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-05-11T21:49:17.263Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.7","versionEndExcluding":"5.10.247"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.7","versionEndExcluding":"5.15.197"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.7","versionEndExcluding":"6.1.159"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.7","versionEndExcluding":"6.6.118"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.7","versionEndExcluding":"6.12.60"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.7","versionEndExcluding":"6.17.10"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.7","versionEndExcluding":"6.18"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}}}}}