CVE-2025-40123
Full vulnerability record from the local CVENow database.
Description
In the Linux kernel, the following vulnerability has been resolved: bpf: Enforce expected_attach_type for tailcall compatibility Yinhao et al. recently reported: Our fuzzer tool discovered an uninitialized pointer issue in the bpf_prog_test_run_xdp() function within the Linux kernel's BPF subsystem. This leads to a NULL pointer dereference when a BPF program attempts to deference the txq member of struct xdp_buff object. The test initializes two programs of BPF_PROG_TYPE_XDP: progA acts as the entry point for bpf_prog_test_run_xdp() and its expected_attach_type can neither be of be BPF_XDP_DEVMAP nor BPF_XDP_CPUMAP. progA calls into a slot of a tailcall map it owns. progB's expected_attach_type must be BPF_XDP_DEVMAP to pass xdp_is_valid_access() validation. The program returns struct xdp_md's egress_ifindex, and the latter is only allowed to be accessed under mentioned expected_attach_type. progB is then inserted into the tailcall which progA calls. The underlying issue goes beyond XDP though. Another example are programs of type BPF_PROG_TYPE_CGROUP_SOCK_ADDR. sock_addr_is_valid_access() as well as sock_addr_func_proto() have different logic depending on the programs' expected_attach_type. Similarly, a program attached to BPF_CGROUP_INET4_GETPEERNAME should not be allowed doing a tailcall into a program which calls bpf_bind() out of BPF which is only enabled for BPF_CGROUP_INET4_CONNECT. In short, specifying expected_attach_type allows to open up additional functionality or restrictions beyond what the basic bpf_prog_type enables. The use of tailcalls must not violate these constraints. Fix it by enforcing expected_attach_type in __bpf_prog_map_compatible(). Note that we only enforce this for tailcall maps, but not for BPF devmaps or cpumaps: There, the programs are invoked through dev_map_bpf_prog_run*() and cpu_map_bpf_prog_run*() which set up a new environment / context and therefore these situations are not prone to this issue.
Severity
HIGH
CVSS score
7.8
(v3.1)
Vulnerability status
Deferred
Source identifier
416baaa9-dc9f-4396-8d5f-8c081fb06d67
Published
2025-11-12 11:15:41.807000
Last modified
2026-10-19 21:10:00.160000
View original CVE JSON
{
"id": "CVE-2025-40123",
"sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"published": "2025-11-12T11:15:41.807",
"lastModified": "2026-10-19T21:10:00.160",
"vulnStatus": "Deferred",
"cveTags": [],
"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."
},
{
"lang": "es",
"value": "En el kernel de Linux, la siguiente vulnerabilidad ha sido resuelta:\n\nbpf: Hacer cumplir expected_attach_type para la compatibilidad de tailcall\n\nYinhao et al. informaron recientemente:\n\n Nuestra herramienta de fuzzing descubrió un problema de puntero no\n inicializado en la función bpf_prog_test_run_xdp() dentro del subsistema\n BPF del kernel de Linux. Esto lleva a una desreferencia de puntero NULL\n cuando un programa BPF intenta desreferenciar el miembro txq del objeto\n struct xdp_buff.\n\nLa prueba inicializa dos programas de BPF_PROG_TYPE_XDP: progA actúa como\npunto de entrada para bpf_prog_test_run_xdp() y su expected_attach_type no\npuede ser ni BPF_XDP_DEVMAP ni BPF_XDP_CPUMAP. progA llama a una ranura de\nun mapa de tailcall que posee. El expected_attach_type de progB debe ser\nBPF_XDP_DEVMAP para pasar la validación de xdp_is_valid_access(). El\nprograma devuelve el egress_ifindex de struct xdp_md, y este último solo\npuede ser accedido bajo el expected_attach_type mencionado. progB se inserta\nentonces en el tailcall al que llama progA.\n\nSin embargo, el problema subyacente va más allá de XDP. Otro ejemplo son los\nprogramas de tipo BPF_PROG_TYPE_CGROUP_SOCK_ADDR. sock_addr_is_valid_access()\nasí como sock_addr_func_proto() tienen lógica diferente dependiendo del\nexpected_attach_type de los programas. De manera similar, un programa\nadjunto a BPF_CGROUP_INET4_GETPEERNAME no debería permitírsele hacer un\ntailcall a un programa que llama a bpf_bind() fuera de BPF, lo cual solo\nestá habilitado para BPF_CGROUP_INET4_CONNECT.\n\nEn resumen, especificar expected_attach_type permite habilitar funcionalidad\no restricciones adicionales más allá de lo que permite el bpf_prog_type\nbásico. El uso de tailcalls no debe violar estas restricciones. Se soluciona\nhaciendo cumplir expected_attach_type en __bpf_prog_map_compatible().\n\nTenga en cuenta que solo hacemos cumplir esto para los mapas de tailcall,\npero no para los devmaps o cpumaps de BPF: Allí, los programas se invocan a\ntravés de dev_map_bpf_prog_run*() y cpu_map_bpf_prog_run*() que configuran\nun nuevo entorno/contexto y, por lo tanto, estas situaciones no son\npropensas a este problema."
}
],
"affected": [
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"affectedData": [
{
"vendor": "Linux",
"product": "Linux",
"defaultStatus": "unaffected",
"programFiles": [
"include/linux/bpf.h",
"kernel/bpf/core.c"
],
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"versions": [
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"versionType": "git",
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},
{
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"product": "Linux",
"defaultStatus": "affected",
"programFiles": [
"include/linux/bpf.h",
"kernel/bpf/core.c"
],
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"versions": [
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},
{
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},
{
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},
{
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},
{
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},
{
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"lessThanOrEqual": "6.6.*",
"versionType": "semver",
"status": "unaffected"
},
{
"version": "6.12.53",
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},
{
"version": "6.17.3",
"lessThanOrEqual": "6.17.*",
"versionType": "semver",
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},
{
"version": "6.18",
"lessThanOrEqual": "*",
"versionType": "original_commit_for_fix",
"status": "unaffected"
}
]
}
]
}
],
"metrics": {
"cvssMetricV31": [
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"type": "Secondary",
"cvssData": {
"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",
"attackVector": "LOCAL",
"attackComplexity": "LOW",
"privilegesRequired": "LOW",
"userInteraction": "NONE",
"scope": "UNCHANGED",
"confidentialityImpact": "HIGH",
"integrityImpact": "HIGH",
"availabilityImpact": "HIGH"
},
"exploitabilityScore": 1.8,
"impactScore": 5.9
}
],
"ssvcV203": [
{
"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
"ssvcData": {
"timestamp": "2026-10-15T21:57:04.979824Z",
"id": "CVE-2025-40123",
"options": [
{
"exploitation": "none"
},
{
"automatable": "no"
},
{
"technicalImpact": "total"
}
],
"role": "CISA Coordinator",
"version": "2.0.3"
}
}
]
},
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