{"id":"CVE-2025-40123","title":"bpf: Enforce expected_attach_type for tailcall compatibility","summary":"In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: Enforce expected_attach_type for tailcall compatibility\n\nYinhao et al. recently reported:\n\n  Our fuzzer tool discovered an uninitialized pointer issue in the\n  bpf…","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","cvssSource":"cna","vendor":"Linux","product":"Linux","affected":["Linux >= 5e43f899b03a3492ce5fc44e8900becb04dae9c0 < e53a59e7cee5c1605d1ed595933098c2b69108f9","Linux >= 5e43f899b03a3492ce5fc44e8900becb04dae9c0 < dc4f348952173beb8ceb15be30b249276eccb605","Linux >= 5e43f899b03a3492ce5fc44e8900becb04dae9c0 < a99de19128aec0913f3d529f529fbbff5edfaff8","Linux >= 5e43f899b03a3492ce5fc44e8900becb04dae9c0 < 08cb3dc9d2b44f153d0bcf2cb966e4a94b5d0f32","Linux >= 5e43f899b03a3492ce5fc44e8900becb04dae9c0 < f856c598080ba7ce1252867b8ecd6ad5bdaf9a6a","Linux >= 5e43f899b03a3492ce5fc44e8900becb04dae9c0 < c1ad19b5d8e23123503dcaf2d4342e1b90b923ad","Linux >= 5e43f899b03a3492ce5fc44e8900becb04dae9c0 < 4540aed51b12bc13364149bf95f6ecef013197c0","Linux 4.17"],"exploitAvailable":true,"published":"2025-11-12","updated":"2026-09-14","sourceUpdated":"2026-09-14T11:58:08.635Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2025-40123","references":[{"url":"https://git.kernel.org/stable/c/e53a59e7cee5c1605d1ed595933098c2b69108f9"},{"url":"https://git.kernel.org/stable/c/dc4f348952173beb8ceb15be30b249276eccb605"},{"url":"https://git.kernel.org/stable/c/a99de19128aec0913f3d529f529fbbff5edfaff8"},{"url":"https://git.kernel.org/stable/c/08cb3dc9d2b44f153d0bcf2cb966e4a94b5d0f32"},{"url":"https://git.kernel.org/stable/c/f856c598080ba7ce1252867b8ecd6ad5bdaf9a6a"},{"url":"https://git.kernel.org/stable/c/c1ad19b5d8e23123503dcaf2d4342e1b90b923ad"},{"url":"https://git.kernel.org/stable/c/4540aed51b12bc13364149bf95f6ecef013197c0"}],"tags":["cve.org","exploit-available"],"epss":0.00155,"epssPercentile":0.05016,"exploits":{"github":1,"githubRepos":["https://github.com/gduma-phData/patch-CVE-2025-40123"],"checkedAt":"2026-09-23T07:13:35.940Z"},"ingestedAt":"2026-09-14T15:23:07.459Z","slug":"CVE-2025-40123","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\nbpf: Enforce expected_attach_type for tailcall compatibility\n\nYinhao et al. recently reported:\n\n  Our fuzzer tool discovered an uninitialized pointer issue in the\n  bpf_prog_test_run_xdp() function within the Linux kernel's BPF subsystem.\n  This leads to a NULL pointer dereference when a BPF program attempts to\n  deference the txq member of struct xdp_buff object.\n\nThe test initializes two programs of BPF_PROG_TYPE_XDP: progA acts as the\nentry point for bpf_prog_test_run_xdp() and its expected_attach_type can\nneither be of be BPF_XDP_DEVMAP nor BPF_XDP_CPUMAP. progA calls into a slot\nof a tailcall map it owns. progB's expected_attach_type must be BPF_XDP_DEVMAP\nto pass xdp_is_valid_access() validation. The program returns struct xdp_md's\negress_ifindex, and the latter is only allowed to be accessed under mentioned\nexpected_attach_type. progB is then inserted into the tailcall which progA\ncalls.\n\nThe underlying issue goes beyond XDP though. Another example are programs\nof type BPF_PROG_TYPE_CGROUP_SOCK_ADDR. sock_addr_is_valid_access() as well\nas sock_addr_func_proto() have different logic depending on the programs'\nexpected_attach_type. Similarly, a program attached to BPF_CGROUP_INET4_GETPEERNAME\nshould not be allowed doing a tailcall into a program which calls bpf_bind()\nout of BPF which is only enabled for BPF_CGROUP_INET4_CONNECT.\n\nIn short, specifying expected_attach_type allows to open up additional\nfunctionality or restrictions beyond what the basic bpf_prog_type enables.\nThe use of tailcalls must not violate these constraints. Fix it by enforcing\nexpected_attach_type in __bpf_prog_map_compatible().\n\nNote that we only enforce this for tailcall maps, but not for BPF devmaps or\ncpumaps: There, the programs are invoked through dev_map_bpf_prog_run*() and\ncpu_map_bpf_prog_run*() which set up a new environment / context and therefore\nthese situations are not prone to this issue.\n\n## Affected\n\n- `Linux >= 5e43f899b03a3492ce5fc44e8900becb04dae9c0 < e53a59e7cee5c1605d1ed595933098c2b69108f9`\n- `Linux >= 5e43f899b03a3492ce5fc44e8900becb04dae9c0 < dc4f348952173beb8ceb15be30b249276eccb605`\n- `Linux >= 5e43f899b03a3492ce5fc44e8900becb04dae9c0 < a99de19128aec0913f3d529f529fbbff5edfaff8`\n- `Linux >= 5e43f899b03a3492ce5fc44e8900becb04dae9c0 < 08cb3dc9d2b44f153d0bcf2cb966e4a94b5d0f32`\n- `Linux >= 5e43f899b03a3492ce5fc44e8900becb04dae9c0 < f856c598080ba7ce1252867b8ecd6ad5bdaf9a6a`\n- `Linux >= 5e43f899b03a3492ce5fc44e8900becb04dae9c0 < c1ad19b5d8e23123503dcaf2d4342e1b90b923ad`\n- `Linux >= 5e43f899b03a3492ce5fc44e8900becb04dae9c0 < 4540aed51b12bc13364149bf95f6ecef013197c0`\n- `Linux 4.17`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"midnight","depthScore":55,"depthScoreParts":{"impact":42.9,"likelihood":0,"exploitation":12,"ransomware":0},"changes":[]}