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vuln-cve/data/2025/40xxx/CVE-2025-40123.json
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{
"dataType": "CVE_RECORD",
"dataVersion": "5.2",
"cveMetadata": {
"cveId": "CVE-2025-40123",
"assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"state": "PUBLISHED",
"assignerShortName": "Linux",
"dateReserved": "2025-04-16T07:20:57.169Z",
"datePublished": "2025-11-12T10:23:19.589Z",
"dateUpdated": "2026-10-15T22:02:38.256Z"
},
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"shortName": "Linux",
"dateUpdated": "2026-09-14T11:58:08.635Z"
},
"descriptions": [
{
"lang": "en",
"value": "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_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."
}
],
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{
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"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"
},
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{
"lang": "en",
"value": "AV:L - The vulnerability is reached through the bpf(2) syscall — loading two programs with differing expected_attach_type, populating a BPF_MAP_TYPE_PROG_ARRAY, and invoking the tail call via BPF_PROG_TEST_RUN or a live attach. No network-supplied data introduces the incompatible tail call, so local access is required.\nAC:L - Exploitation is fully deterministic: the attacker authors and loads both programs, owns the prog array, and controls exactly when the tail call executes; there is no race and no memory-layout condition needed for the mis-typed context dereference to occur.\nPR:L - A basic local user with BPF program-loading access can create the prog array and the two mismatched programs; this matches the established scoring of comparable BPF verifier-constraint bypasses, and containerized/delegated-token deployments grant exactly this level without full administrative rights.\nUI:N - The attacker performs every step — program load, map update, and program invocation — entirely on their own; no victim action or cooperation is involved.\nS:U - The mis-typed context dereference and any resulting corruption occur within the kernel that is already the vulnerable component, so impact stays inside a single security authority.\nC:H - xdp_init_buff() never initializes xdp_buff->txq, so a tail-called BPF_XDP_DEVMAP program reading egress_ifindex dereferences attacker-groomable uninitialized stack memory twice and returns the resulting kernel dword into BPF, which can be exfiltrated through a map — an effectively arbitrary kernel read primitive.\nI:H - Bypassing expected_attach_type lets a program execute helpers and context writes the running hook never validated — e.g. bpf_bind()/__inet_bind() invoked from a GETPEERNAME hook mutates live socket binding and hash state without the socket lock, and msg_src_ip4/6 or sockopt level/optname/retval writes land on NULL or wrong-type kernel fields.\nA:H - The reported case is an immediate NULL pointer dereference on xdp_buff->txq in bpf_prog_test_run_xdp(), and in driver XDP paths the uninitialized txq produces a wild pointer dereference — either way a kernel oops that the attacker can trigger repeatedly."
}
]
}
],
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"product": "Linux",
"vendor": "Linux",
"defaultStatus": "unaffected",
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
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],
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"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
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],
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{
"version": "5.10.270",
"lessThanOrEqual": "5.10.*",
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},
{
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"lessThanOrEqual": "5.15.*",
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},
{
"version": "6.1.156",
"lessThanOrEqual": "6.1.*",
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},
{
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"lessThanOrEqual": "6.6.*",
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},
{
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},
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"status": "unaffected",
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},
{
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"lessThanOrEqual": "*",
"status": "unaffected",
"versionType": "original_commit_for_fix"
}
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"references": [
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"url": "https://git.kernel.org/stable/c/e53a59e7cee5c1605d1ed595933098c2b69108f9"
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"url": "https://git.kernel.org/stable/c/dc4f348952173beb8ceb15be30b249276eccb605"
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{
"url": "https://git.kernel.org/stable/c/4540aed51b12bc13364149bf95f6ecef013197c0"
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"title": "bpf: Enforce expected_attach_type for tailcall compatibility",
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"content": {
"id": "CVE-2025-40123",
"role": "CISA Coordinator",
"options": [
{
"Exploitation": "none"
},
{
"Automatable": "no"
},
{
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}
],
"version": "2.0.3",
"timestamp": "2026-10-15T21:57:04.979824Z"
}
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}
],
"title": "CISA ADP Vulnrichment",
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