CVE-2025-40214 (GCVE-0-2025-40214)

Vulnerability from cvelistv5 – Published: 2025-12-04 12:38 – Updated: 2026-08-05 12:08
VLAI
Title
af_unix: Initialise scc_index in unix_add_edge().
Summary
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.
Severity
7.8 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Assigner
Linux CNA under the mitre root
CNA scorecard D 53/100 over 7061 records in the last 180 days details
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: adfb68b39b39767d6bfb53e48c4f19c183765686 , < 20003fbb9174121b27bd1da6ebe61542ac4c327d (git)
Affected: d23802221f6755e104606864067c71af8cdb6788 , < 4cd8d755c7d4f515dd9abf483316aca2f1b7b0f3 (git)
Affected: ad081928a8b0f57f269df999a28087fce6f2b6ce , < db81ad20fd8aef7cc7d536c52ee5ea4c1f979128 (git)
Affected: ad081928a8b0f57f269df999a28087fce6f2b6ce , < 1aa7e40ee850c9053e769957ce6541173891204d (git)
Affected: ad081928a8b0f57f269df999a28087fce6f2b6ce , < 60e6489f8e3b086bd1130ad4450a2c112e863791 (git)
Affected: 6.1.141 , < 6.1.159 (semver)
Affected: 6.6.93 , < 6.6.117 (semver)
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Linux Linux Affected: 6.10
Unaffected: 0 , < 6.10 (semver)
Unaffected: 6.1.159 , ≤ 6.1.* (semver)
Unaffected: 6.6.117 , ≤ 6.6.* (semver)
Unaffected: 6.12.59 , ≤ 6.12.* (semver)
Unaffected: 6.17.9 , ≤ 6.17.* (semver)
Unaffected: 6.18 , ≤ * (original_commit_for_fix)
guessed Create a notification for this product.
Siemens RUGGEDCOM RST2428P Affected: 0 , < V4.0 (custom)
guessed Create a notification for this product.
Show details on NVD website
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          "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)-\u003evertex-\u003escc_index = 2 (UNIX_VERTEX_INDEX_START)\n  unix_sk(sk-X)-\u003evertex-\u003escc_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\u0027s\ncyclic self-reference, which makes close() trigger GC.\n\nAt 3-b, unix_add_edge() allocates unix_sk(sk-B)-\u003evertex 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\u0027s listener and sk-C are not in-flight.\n\n3-c decrements sk-A\u0027s 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 -\u003e sk-B (-\u003e sk-C)\n  sk-X -\u003e 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)-\u003escc_index == unix_sk(sk-B)-\u003escc_index \u003c-- Wrong!\n  \u0026\u0026\n  sk-A\u0027s file refcnt == unix_sk(sk-A)-\u003evertex-\u003eout_degree\n                                       ^-- 1 in-flight count for sk-B\n  -\u003e 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-\u003escc_index == 2 (UNIX_VERTEX_INDEX_START)\nset by unix_walk_scc() at 1-c.\n\nLet\u0027s track the max SCC index from the previous unix_walk_scc()\ncall and assign the max + 1 to a new vertex\u0027s scc_index.\n\nThis way, we can continue to avoid Tarjan\u0027s algorithm while\npreventing misjudgments."
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              "value": "AV:L - The entire attack is driven by local syscalls on AF_UNIX sockets \u2014 socketpair/connect/accept, sendmsg with SCM_RIGHTS, close \u2014 which is a purely local IPC interface with no remote or adjacent-network reachability.\nAC:L - The attacker controls every stage: the spray allocates and frees the exact same `struct unix_vertex` slab objects that `unix_prepare_fpl()` then reallocates from a LIFO freelist with `scc_index` already set to UNIX_VERTEX_INDEX_START, and the self-referencing socket makes every close() deterministically trigger GC, so no condition lies outside the attacker\u0027s control.\nPR:L - Only an ordinary unprivileged local account is needed \u2014 AF_UNIX socket creation and SCM_RIGHTS fd passing require no capability, no user namespace, and no configuration, and the path is fully reachable from inside containers, sandboxes, and Android app processes.\nUI:N - The attacker\u0027s own process performs all of the socket creation, fd passing, accept(), and close() operations; no action by any other user or victim process is required.\nS:U - The prematurely freed skbs, the dangling `u-\u003eoob_skb`, and the vulnerable GC code all live in the kernel\u0027s own security authority, so this is standard local kernel privilege escalation with no boundary crossing.\nC:H - `unix_stream_recv_urg()` passes the dangling `u-\u003eoob_skb` to `recv_actor()`, copying data from a freed-and-reclaimed skb to userspace, and also reads `oob_skb-\u003eprev`; with the freed object groomed to hold a controlled `-\u003edata`/`-\u003elen`, this yields arbitrary kernel memory disclosure.\nI:H - The same path writes through freed memory \u2014 `UNIXCB(oob_skb).consumed += 1` and `__skb_unlink()` performing `prev-\u003enext = next; next-\u003eprev = prev` with attacker-groomed pointers \u2014 giving a use-after-free unlink write primitive suitable for control-flow hijack, on top of silently destroying a live socket\u0027s queued messages.\nA:H - Freeing an alive socket\u0027s receive queue leaves `u-\u003eoob_skb` and `u-\u003einq_len` inconsistent with a purged queue; subsequent operations dereference freed skbs, reliably producing KASAN splats, oopses, and kernel panics."
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          {
            "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)-\u003evertex-\u003escc_index = 2 (UNIX_VERTEX_INDEX_START)\n  unix_sk(sk-X)-\u003evertex-\u003escc_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\u0027s\ncyclic self-reference, which makes close() trigger GC.\n\nAt 3-b, unix_add_edge() allocates unix_sk(sk-B)-\u003evertex 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\u0027s listener and sk-C are not in-flight.\n\n3-c decrements sk-A\u0027s 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 -\u003e sk-B (-\u003e sk-C)\n  sk-X -\u003e 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)-\u003escc_index == unix_sk(sk-B)-\u003escc_index \u003c-- Wrong!\n  \u0026\u0026\n  sk-A\u0027s file refcnt == unix_sk(sk-A)-\u003evertex-\u003eout_degree\n                                       ^-- 1 in-flight count for sk-B\n  -\u003e 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-\u003escc_index == 2 (UNIX_VERTEX_INDEX_START)\nset by unix_walk_scc() at 1-c.\n\nLet\u0027s track the max SCC index from the previous unix_walk_scc()\ncall and assign the max + 1 to a new vertex\u0027s scc_index.\n\nThis way, we can continue to avoid Tarjan\u0027s 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 inform\u00f3 que el GC de AF_UNIX podr\u00eda recolectar basura de una cola de recepci\u00f3n de un socket activo en tr\u00e1nsito, con una buena reproducci\u00f3n.\n\nLa reproducci\u00f3n consta de tres etapas.\n\n  1)\n    1-a. Crear una \u00fanica referencia c\u00edclica 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 embri\u00f3n\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 embri\u00f3n\n    3-b. Pasar sk-B a sk-C\n    3-c. close() el sk-A en tr\u00e1nsito\n    3-d. Activar el GC\n\nA partir de 2-c, sk-A y sk-X est\u00e1n vinculados a unix_unvisited_vertices, y unix_walk_scc() los agrupa en dos SCCs diferentes:\n\n  unix_sk(sk-A)-\u003evertex-\u003escc_index = 2 (UNIX_VERTEX_INDEX_START)\n  unix_sk(sk-X)-\u003evertex-\u003escc_index = 3\n\nUna vez que el GC se completa, unix_graph_grouped se establece en true. Adem\u00e1s, unix_graph_maybe_cyclic se establece en true debido a la autorreferencia c\u00edclica de sk-X, lo que hace que close() active el GC.\n\nEn 3-b, unix_add_edge() asigna unix_sk(sk-B)-\u003evertex 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 est\u00e1n en tr\u00e1nsito.\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 -\u003e sk-B (-\u003e sk-C)\n  sk-X -\u003e sk-X\n\nEsto est\u00e1 totalmente bien. Todos ellos a\u00fan no han sido close()d y deber\u00edan agruparse en diferentes SCCs.\n\nSin embargo, unix_vertex_dead() juzga err\u00f3neamente que sk-A y sk-B est\u00e1n en el mismo SCC y que sk-A est\u00e1 muerto.\n\n  unix_sk(sk-A)-\u003escc_index == unix_sk(sk-B)-\u003escc_index \u003c-- \u00a1Incorrecto!\n  \u0026\u0026\n  el refcnt de archivo de sk-A == unix_sk(sk-A)-\u003evertex-\u003eout_degree\n                                       ^-- 1 conteo en tr\u00e1nsito para sk-B\n  -\u003e \u00a1\u00bfsk-A est\u00e1 muerto?!\n\nEl problema es que unix_add_edge() no inicializa scc_index.\n\nLa etapa 1) se utiliza para el \u201cheap spraying\u201d, haciendo que un v\u00e9rtice reci\u00e9n asignado tenga vertex-\u003escc_index == 2 (UNIX_VERTEX_INDEX_START) establecido por unix_walk_scc() en 1-c.\n\nRastreemos el \u00edndice SCC m\u00e1ximo de la llamada anterior a unix_walk_scc() y asignemos el m\u00e1ximo + 1 al scc_index de un nuevo v\u00e9rtice.\n\nDe esta manera, podemos seguir evitando el algoritmo de Tarjan mientras prevenimos juicios err\u00f3neos."
          }
        ],
        "id": "CVE-2025-40214",
        "lastModified": "2026-10-19T21:10:00.160",
        "metrics": {
          "cvssMetricV31": [
            {
              "cvssData": {
                "attackComplexity": "LOW",
                "attackVector": "LOCAL",
                "availabilityImpact": "HIGH",
                "baseScore": 7.8,
                "baseSeverity": "HIGH",
                "confidentialityImpact": "HIGH",
                "integrityImpact": "HIGH",
                "privilegesRequired": "LOW",
                "scope": "UNCHANGED",
                "userInteraction": "NONE",
                "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
                "version": "3.1"
              },
              "exploitabilityScore": 1.8,
              "impactScore": 5.9,
              "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
              "type": "Secondary"
            }
          ]
        },
        "published": "2025-12-04T13:15:48.157",
        "references": [
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/1aa7e40ee850c9053e769957ce6541173891204d"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/20003fbb9174121b27bd1da6ebe61542ac4c327d"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/4cd8d755c7d4f515dd9abf483316aca2f1b7b0f3"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/60e6489f8e3b086bd1130ad4450a2c112e863791"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/db81ad20fd8aef7cc7d536c52ee5ea4c1f979128"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://mohandacherir.github.io/Qdiv7/posts/unix_new_gc/"
          },
          {
            "source": "0b142b55-0307-4c5a-b3c9-f314f3fb7c5e",
            "url": "https://cert-portal.siemens.com/productcert/html/ssa-253495.html"
          }
        ],
        "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "vulnStatus": "Deferred"
      }
    },
    "redhat_vex": {
      "aggregate_severity": "Moderate",
      "current_release_date": "2026-07-30T08:47:31+00:00",
      "cve": "CVE-2025-40214",
      "id": "CVE-2025-40214",
      "initial_release_date": "2025-12-04T00:00:00+00:00",
      "product_status:known_affected": "90",
      "product_status:known_not_affected": "184",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: af_unix: Initialise scc_index in unix_add_edge()",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2025/cve-2025-40214.json",
      "version": "3"
    }
  }
}



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