{"id":"CVE-2023-52523","title":"In the Linux kernel, the following vulnerability has been resolved:\n\nbpf, sockmap: Reject sk_msg egress redirects to non-TCP sockets\n\nWith a SOCKMAP/SOCKHASH map and an sk_msg program user can steer messages\nsent from one TCP socket (s1)…","summary":"In the Linux kernel, the following vulnerability has been resolved:\n\nbpf, sockmap: Reject sk_msg egress redirects to non-TCP sockets\n\nWith a SOCKMAP/SOCKHASH map and an sk_msg program user can steer messages\nsent from one TCP socket (s1)…","severity":"high","cvss":7.8,"cvssVector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","cwe":["CWE-476"],"vendor":"linux","product":"linux_kernel","affected":["linux_kernel >= 5.13, < 5.15.135","linux_kernel >= 5.16, < 6.1.57","linux_kernel >= 6.2, < 6.5.7","linux_kernel = 6.6"],"patched":["linux_kernel 6.5.7"],"published":"2024-03-02","updated":"2026-08-04","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2023-52523","references":[{"url":"https://git.kernel.org/stable/c/b80e31baa43614e086a9d29dc1151932b1bd7fc5","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/b8f97e47b6fb84fcf2f5a22e725eefb6cf5070c2","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/bc8b89b6963803a123f64aa9494155a037b3d728","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/ded6e448028f0f91b6af35985afca01fa02a9089","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/b80e31baa43614e086a9d29dc1151932b1bd7fc5","label":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://git.kernel.org/stable/c/b8f97e47b6fb84fcf2f5a22e725eefb6cf5070c2","label":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://git.kernel.org/stable/c/bc8b89b6963803a123f64aa9494155a037b3d728","label":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://git.kernel.org/stable/c/ded6e448028f0f91b6af35985afca01fa02a9089","label":"af854a3a-2127-422b-91ae-364da2661108"}],"tags":["nvd"],"epss":0.00236,"epssPercentile":0.14881,"ingestedAt":"2026-08-05T05:58:02.184Z","slug":"CVE-2023-52523","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\nbpf, sockmap: Reject sk_msg egress redirects to non-TCP sockets\n\nWith a SOCKMAP/SOCKHASH map and an sk_msg program user can steer messages\nsent from one TCP socket (s1) to actually egress from another TCP\nsocket (s2):\n\ntcp_bpf_sendmsg(s1)\t\t// = sk_prot->sendmsg\n  tcp_bpf_send_verdict(s1)\t// __SK_REDIRECT case\n    tcp_bpf_sendmsg_redir(s2)\n      tcp_bpf_push_locked(s2)\n\ttcp_bpf_push(s2)\n\t  tcp_rate_check_app_limited(s2) // expects tcp_sock\n\t  tcp_sendmsg_locked(s2)\t // ditto\n\nThere is a hard-coded assumption in the call-chain, that the egress\nsocket (s2) is a TCP socket.\n\nHowever in commit 122e6c79efe1 (\"sock_map: Update sock type checks for\nUDP\") we have enabled redirects to non-TCP sockets. This was done for the\nsake of BPF sk_skb programs. There was no indention to support sk_msg\nsend-to-egress use case.\n\nAs a result, attempts to send-to-egress through a non-TCP socket lead to a\ncrash due to invalid downcast from sock to tcp_sock:\n\n BUG: kernel NULL pointer dereference, address: 000000000000002f\n ...\n Call Trace:\n  <TASK>\n  ? show_regs+0x60/0x70\n  ? __die+0x1f/0x70\n  ? page_fault_oops+0x80/0x160\n  ? do_user_addr_fault+0x2d7/0x800\n  ? rcu_is_watching+0x11/0x50\n  ? exc_page_fault+0x70/0x1c0\n  ? asm_exc_page_fault+0x27/0x30\n  ? tcp_tso_segs+0x14/0xa0\n  tcp_write_xmit+0x67/0xce0\n  __tcp_push_pending_frames+0x32/0xf0\n  tcp_push+0x107/0x140\n  tcp_sendmsg_locked+0x99f/0xbb0\n  tcp_bpf_push+0x19d/0x3a0\n  tcp_bpf_sendmsg_redir+0x55/0xd0\n  tcp_bpf_send_verdict+0x407/0x550\n  tcp_bpf_sendmsg+0x1a1/0x390\n  inet_sendmsg+0x6a/0x70\n  sock_sendmsg+0x9d/0xc0\n  ? sockfd_lookup_light+0x12/0x80\n  __sys_sendto+0x10e/0x160\n  ? syscall_enter_from_user_mode+0x20/0x60\n  ? __this_cpu_preempt_check+0x13/0x20\n  ? lockdep_hardirqs_on+0x82/0x110\n  __x64_sys_sendto+0x1f/0x30\n  do_syscall_64+0x38/0x90\n  entry_SYSCALL_64_after_hwframe+0x63/0xcd\n\nReject selecting a non-TCP sockets as redirect target from a BPF sk_msg\nprogram to prevent the crash. When attempted, user will receive an EACCES\nerror from send/sendto/sendmsg() syscall.\n\n## Affected\n\n- `linux_kernel >= 5.13, < 5.15.135`\n- `linux_kernel >= 5.16, < 6.1.57`\n- `linux_kernel >= 6.2, < 6.5.7`\n- `linux_kernel = 6.6`\n\n## Remediation\n\nUpgrade past the affected range:\n\n- `linux_kernel 6.5.7`","depth":"twilight","depthScore":43,"depthScoreParts":{"impact":42.9,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}