CVE-2025-40214
Full vulnerability record from the local CVENow database.
Description
In the Linux kernel, the following vulnerability has been resolved: af_unix: Initialise scc_index in unix_add_edge(). Quang Le reported that the AF_UNIX GC could garbage-collect a receive queue of an alive in-flight socket, with a nice repro. The repro consists of three stages. 1) 1-a. Create a single cyclic reference with many sockets 1-b. close() all sockets 1-c. Trigger GC 2) 2-a. Pass sk-A to an embryo sk-B 2-b. Pass sk-X to sk-X 2-c. Trigger GC 3) 3-a. accept() the embryo sk-B 3-b. Pass sk-B to sk-C 3-c. close() the in-flight sk-A 3-d. Trigger GC As of 2-c, sk-A and sk-X are linked to unix_unvisited_vertices, and unix_walk_scc() groups them into two different SCCs: unix_sk(sk-A)->vertex->scc_index = 2 (UNIX_VERTEX_INDEX_START) unix_sk(sk-X)->vertex->scc_index = 3 Once GC completes, unix_graph_grouped is set to true. Also, unix_graph_maybe_cyclic is set to true due to sk-X's cyclic self-reference, which makes close() trigger GC. At 3-b, unix_add_edge() allocates unix_sk(sk-B)->vertex and links it to unix_unvisited_vertices. unix_update_graph() is called at 3-a. and 3-b., but neither unix_graph_grouped nor unix_graph_maybe_cyclic is changed because both sk-B's listener and sk-C are not in-flight. 3-c decrements sk-A's file refcnt to 1. Since unix_graph_grouped is true at 3-d, unix_walk_scc_fast() is finally called and iterates 3 sockets sk-A, sk-B, and sk-X: sk-A -> sk-B (-> sk-C) sk-X -> sk-X This is totally fine. All of them are not yet close()d and should be grouped into different SCCs. However, unix_vertex_dead() misjudges that sk-A and sk-B are in the same SCC and sk-A is dead. unix_sk(sk-A)->scc_index == unix_sk(sk-B)->scc_index <-- Wrong! && sk-A's file refcnt == unix_sk(sk-A)->vertex->out_degree ^-- 1 in-flight count for sk-B -> sk-A is dead !? The problem is that unix_add_edge() does not initialise scc_index. Stage 1) is used for heap spraying, making a newly allocated vertex have vertex->scc_index == 2 (UNIX_VERTEX_INDEX_START) set by unix_walk_scc() at 1-c. Let's track the max SCC index from the previous unix_walk_scc() call and assign the max + 1 to a new vertex's scc_index. This way, we can continue to avoid Tarjan's algorithm while preventing misjudgments.
View original CVE JSON
{
"id": "CVE-2025-40214",
"sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"published": "2025-12-04T13:15:48.157",
"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\naf_unix: Initialise scc_index in unix_add_edge().\n\nQuang Le reported that the AF_UNIX GC could garbage-collect a\nreceive queue of an alive in-flight socket, with a nice repro.\n\nThe repro consists of three stages.\n\n 1)\n 1-a. Create a single cyclic reference with many sockets\n 1-b. close() all sockets\n 1-c. Trigger GC\n\n 2)\n 2-a. Pass sk-A to an embryo sk-B\n 2-b. Pass sk-X to sk-X\n 2-c. Trigger GC\n\n 3)\n 3-a. accept() the embryo sk-B\n 3-b. Pass sk-B to sk-C\n 3-c. close() the in-flight sk-A\n 3-d. Trigger GC\n\nAs of 2-c, sk-A and sk-X are linked to unix_unvisited_vertices,\nand unix_walk_scc() groups them into two different SCCs:\n\n unix_sk(sk-A)->vertex->scc_index = 2 (UNIX_VERTEX_INDEX_START)\n unix_sk(sk-X)->vertex->scc_index = 3\n\nOnce GC completes, unix_graph_grouped is set to true.\nAlso, unix_graph_maybe_cyclic is set to true due to sk-X's\ncyclic self-reference, which makes close() trigger GC.\n\nAt 3-b, unix_add_edge() allocates unix_sk(sk-B)->vertex and\nlinks it to unix_unvisited_vertices.\n\nunix_update_graph() is called at 3-a. and 3-b., but neither\nunix_graph_grouped nor unix_graph_maybe_cyclic is changed\nbecause both sk-B's listener and sk-C are not in-flight.\n\n3-c decrements sk-A's file refcnt to 1.\n\nSince unix_graph_grouped is true at 3-d, unix_walk_scc_fast()\nis finally called and iterates 3 sockets sk-A, sk-B, and sk-X:\n\n sk-A -> sk-B (-> sk-C)\n sk-X -> sk-X\n\nThis is totally fine. All of them are not yet close()d and\nshould be grouped into different SCCs.\n\nHowever, unix_vertex_dead() misjudges that sk-A and sk-B are\nin the same SCC and sk-A is dead.\n\n unix_sk(sk-A)->scc_index == unix_sk(sk-B)->scc_index <-- Wrong!\n &&\n sk-A's file refcnt == unix_sk(sk-A)->vertex->out_degree\n ^-- 1 in-flight count for sk-B\n -> sk-A is dead !?\n\nThe problem is that unix_add_edge() does not initialise scc_index.\n\nStage 1) is used for heap spraying, making a newly allocated\nvertex have vertex->scc_index == 2 (UNIX_VERTEX_INDEX_START)\nset by unix_walk_scc() at 1-c.\n\nLet's track the max SCC index from the previous unix_walk_scc()\ncall and assign the max + 1 to a new vertex's scc_index.\n\nThis way, we can continue to avoid Tarjan's algorithm while\npreventing misjudgments."
},
{
"lang": "es",
"value": "En el kernel de Linux, la siguiente vulnerabilidad ha sido resuelta:\n\naf_unix: Inicializar scc_index en unix_add_edge().\n\nQuang Le informó que el GC de AF_UNIX podría recolectar basura de una cola de recepción de un socket activo en tránsito, con una buena reproducción.\n\nLa reproducción consta de tres etapas.\n\n 1)\n 1-a. Crear una única referencia cíclica con muchos sockets\n 1-b. close() todos los sockets\n 1-c. Activar el GC\n\n 2)\n 2-a. Pasar sk-A a un sk-B embrión\n 2-b. Pasar sk-X a sk-X\n 2-c. Activar el GC\n\n 3)\n 3-a. accept() el sk-B embrión\n 3-b. Pasar sk-B a sk-C\n 3-c. close() el sk-A en tránsito\n 3-d. Activar el GC\n\nA partir de 2-c, sk-A y sk-X están vinculados a unix_unvisited_vertices, y unix_walk_scc() los agrupa en dos SCCs diferentes:\n\n unix_sk(sk-A)->vertex->scc_index = 2 (UNIX_VERTEX_INDEX_START)\n unix_sk(sk-X)->vertex->scc_index = 3\n\nUna vez que el GC se completa, unix_graph_grouped se establece en true. Además, unix_graph_maybe_cyclic se establece en true debido a la autorreferencia cíclica de sk-X, lo que hace que close() active el GC.\n\nEn 3-b, unix_add_edge() asigna unix_sk(sk-B)->vertex y lo vincula a unix_unvisited_vertices.\n\nunix_update_graph() se llama en 3-a. y 3-b., pero ni unix_graph_grouped ni unix_graph_maybe_cyclic se modifican porque tanto el listener de sk-B como sk-C no están en tránsito.\n\n3-c decrementa el refcnt de archivo de sk-A a 1.\n\nDado que unix_graph_grouped es true en 3-d, unix_walk_scc_fast() finalmente se llama e itera 3 sockets sk-A, sk-B y sk-X:\n\n sk-A -> sk-B (-> sk-C)\n sk-X -> sk-X\n\nEsto está totalmente bien. Todos ellos aún no han sido close()d y deberían agruparse en diferentes SCCs.\n\nSin embargo, unix_vertex_dead() juzga erróneamente que sk-A y sk-B están en el mismo SCC y que sk-A está muerto.\n\n unix_sk(sk-A)->scc_index == unix_sk(sk-B)->scc_index <-- ¡Incorrecto!\n &&\n el refcnt de archivo de sk-A == unix_sk(sk-A)->vertex->out_degree\n ^-- 1 conteo en tránsito para sk-B\n -> ¡¿sk-A está muerto?!\n\nEl problema es que unix_add_edge() no inicializa scc_index.\n\nLa etapa 1) se utiliza para el “heap spraying”, haciendo que un vértice recién asignado tenga vertex->scc_index == 2 (UNIX_VERTEX_INDEX_START) establecido por unix_walk_scc() en 1-c.\n\nRastreemos el índice SCC máximo de la llamada anterior a unix_walk_scc() y asignemos el máximo + 1 al scc_index de un nuevo vértice.\n\nDe esta manera, podemos seguir evitando el algoritmo de Tarjan mientras prevenimos juicios erróneos."
}
],
"affected": [
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"affectedData": [
{
"vendor": "Linux",
"product": "Linux",
"defaultStatus": "unaffected",
"programFiles": [
"net/unix/garbage.c"
],
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"versions": [
{
"version": "adfb68b39b39767d6bfb53e48c4f19c183765686",
"lessThan": "20003fbb9174121b27bd1da6ebe61542ac4c327d",
"versionType": "git",
"status": "affected"
},
{
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"lessThan": "4cd8d755c7d4f515dd9abf483316aca2f1b7b0f3",
"versionType": "git",
"status": "affected"
},
{
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"versionType": "git",
"status": "affected"
},
{
"version": "ad081928a8b0f57f269df999a28087fce6f2b6ce",
"lessThan": "1aa7e40ee850c9053e769957ce6541173891204d",
"versionType": "git",
"status": "affected"
},
{
"version": "ad081928a8b0f57f269df999a28087fce6f2b6ce",
"lessThan": "60e6489f8e3b086bd1130ad4450a2c112e863791",
"versionType": "git",
"status": "affected"
},
{
"version": "6.1.141",
"lessThan": "6.1.159",
"versionType": "semver",
"status": "affected"
},
{
"version": "6.6.93",
"lessThan": "6.6.117",
"versionType": "semver",
"status": "affected"
}
]
},
{
"vendor": "Linux",
"product": "Linux",
"defaultStatus": "affected",
"programFiles": [
"net/unix/garbage.c"
],
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"versions": [
{
"version": "6.10",
"status": "affected"
},
{
"version": "0",
"lessThan": "6.10",
"versionType": "semver",
"status": "unaffected"
},
{
"version": "6.1.159",
"lessThanOrEqual": "6.1.*",
"versionType": "semver",
"status": "unaffected"
},
{
"version": "6.6.117",
"lessThanOrEqual": "6.6.*",
"versionType": "semver",
"status": "unaffected"
},
{
"version": "6.12.59",
"lessThanOrEqual": "6.12.*",
"versionType": "semver",
"status": "unaffected"
},
{
"version": "6.17.9",
"lessThanOrEqual": "6.17.*",
"versionType": "semver",
"status": "unaffected"
},
{
"version": "6.18",
"lessThanOrEqual": "*",
"versionType": "original_commit_for_fix",
"status": "unaffected"
}
]
}
]
},
{
"source": "0b142b55-0307-4c5a-b3c9-f314f3fb7c5e",
"affectedData": [
{
"vendor": "Siemens",
"product": "RUGGEDCOM RST2428P",
"defaultStatus": "unknown",
"versions": [
{
"version": "0",
"lessThan": "V4.0",
"versionType": "custom",
"status": "affected"
}
]
}
]
}
],
"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
}
]
},
"references": [
{
"url": "https://git.kernel.org/stable/c/1aa7e40ee850c9053e769957ce6541173891204d",
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"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
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{
"url": "https://mohandacherir.github.io/Qdiv7/posts/unix_new_gc/",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://cert-portal.siemens.com/productcert/html/ssa-253495.html",
"source": "0b142b55-0307-4c5a-b3c9-f314f3fb7c5e"
}
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}