{"id":"CVE-2021-47593","state":"PUBLISHED","title":"mptcp: clear 'kern' flag from fallback sockets","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nmptcp: clear 'kern' flag from fallback sockets\n\nThe mptcp ULP extension relies on sk->sk_sock_kern being set correctly:\nIt prevents setsockopt(fd, IPPROTO_TCP, TCP_ULP, \"mptcp\", 6); from\nworking for plain tcp sockets (any userspace-exposed socket).\n\nBut in case of fallback, accept() can return a plain tcp sk.\nIn such case, sk is still tagged as 'kernel' and setsockopt will work.\n\nThis will crash the kernel, The subflow extension has a NULL ctx->conn\nmptcp socket:\n\nBUG: KASAN: null-ptr-deref in subflow_data_ready+0x181/0x2b0\nCall Trace:\n tcp_data_ready+0xf8/0x370\n [..]","publishedAt":"2024-06-19T14:53:56.251Z","updatedAt":"2026-05-11T13:57:32.587Z","severity":null,"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"cf7da0d66cc1a2a19fc5930bb746ffbb2d4cd1be","status":"affected","lessThan":"451f1eded7f56e93aaf52eb547ba97742d9c0e97","versionType":"git"},{"version":"cf7da0d66cc1a2a19fc5930bb746ffbb2d4cd1be","status":"affected","lessThan":"c26ac0ea3a91c210cf90452e625dc441adf3e549","versionType":"git"},{"version":"cf7da0d66cc1a2a19fc5930bb746ffbb2d4cd1be","status":"affected","lessThan":"d6692b3b97bdc165d150f4c1505751a323a80717","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":"5.6","status":"affected"},{"version":"0","status":"unaffected","lessThan":"5.6","versionType":"semver"},{"version":"5.10.88","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.11","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"5.16","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/451f1eded7f56e93aaf52eb547ba97742d9c0e97","https://git.kernel.org/stable/c/c26ac0ea3a91c210cf90452e625dc441adf3e549","https://git.kernel.org/stable/c/d6692b3b97bdc165d150f4c1505751a323a80717"],"weaknesses":[],"ingestedAt":"2026-10-29T19:49:19.404Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2021/47xxx/CVE-2021-47593.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2021-47593","state":"PUBLISHED","datePublished":"2024-06-19T14:53:56.251Z","dateUpdated":"2026-05-11T13:57:32.587Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2024-05-24T15:11:00.733Z"},"containers":{"cna":{"title":"mptcp: clear 'kern' flag from fallback sockets","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nmptcp: clear 'kern' flag from fallback sockets\n\nThe mptcp ULP extension relies on sk->sk_sock_kern being set correctly:\nIt prevents setsockopt(fd, IPPROTO_TCP, TCP_ULP, \"mptcp\", 6); from\nworking for plain tcp sockets (any userspace-exposed socket).\n\nBut in case of fallback, accept() can return a plain tcp sk.\nIn such case, sk is still tagged as 'kernel' and setsockopt will work.\n\nThis will crash the kernel, The subflow extension has a NULL ctx->conn\nmptcp socket:\n\nBUG: KASAN: null-ptr-deref in subflow_data_ready+0x181/0x2b0\nCall Trace:\n tcp_data_ready+0xf8/0x370\n [..]"}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"cf7da0d66cc1a2a19fc5930bb746ffbb2d4cd1be","status":"affected","lessThan":"451f1eded7f56e93aaf52eb547ba97742d9c0e97","versionType":"git"},{"version":"cf7da0d66cc1a2a19fc5930bb746ffbb2d4cd1be","status":"affected","lessThan":"c26ac0ea3a91c210cf90452e625dc441adf3e549","versionType":"git"},{"version":"cf7da0d66cc1a2a19fc5930bb746ffbb2d4cd1be","status":"affected","lessThan":"d6692b3b97bdc165d150f4c1505751a323a80717","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":"5.6","status":"affected"},{"version":"0","status":"unaffected","lessThan":"5.6","versionType":"semver"},{"version":"5.10.88","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.11","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"5.16","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/451f1eded7f56e93aaf52eb547ba97742d9c0e97"},{"url":"https://git.kernel.org/stable/c/c26ac0ea3a91c210cf90452e625dc441adf3e549"},{"url":"https://git.kernel.org/stable/c/d6692b3b97bdc165d150f4c1505751a323a80717"}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-05-11T13:57:32.587Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.6","versionEndExcluding":"5.10.88"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.6","versionEndExcluding":"5.15.11"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.6","versionEndExcluding":"5.16"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}},"adp":[{"title":"CVE Program Container","references":[{"url":"https://git.kernel.org/stable/c/451f1eded7f56e93aaf52eb547ba97742d9c0e97","tags":["x_transferred"]},{"url":"https://git.kernel.org/stable/c/c26ac0ea3a91c210cf90452e625dc441adf3e549","tags":["x_transferred"]},{"url":"https://git.kernel.org/stable/c/d6692b3b97bdc165d150f4c1505751a323a80717","tags":["x_transferred"]}],"providerMetadata":{"shortName":"CVE","orgId":"af854a3a-2127-422b-91ae-364da2661108","dateUpdated":"2024-08-04T05:47:39.485Z"}},{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"id":"CVE-2021-47593","role":"CISA Coordinator","options":[{"Exploitation":"none"},{"Automatable":"no"},{"Technical Impact":"partial"}],"version":"2.0.3","timestamp":"2024-09-10T17:12:30.519015Z"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2024-09-11T17:34:52.236Z"}}]}}}