CVE-2025-40214: Software Security Vulnerability Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-g3xr-84mj-fvx6",
  "modified" : "2026-07-30T06:32:18Z",
  "published" : "2025-12-04T15:30:32Z",
  "aliases" : [ "CVE-2025-40214" ],
  "details" : "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.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"
  } ],
  "affected" : [ ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2025-40214"
  }, {
    "type" : "WEB",
    "url" : "https://cert-portal.siemens.com/productcert/html/ssa-253495.html"
  }, {
    "type" : "WEB",
    "url" : "https://git.kernel.org/stable/c/1aa7e40ee850c9053e769957ce6541173891204d"
  }, {
    "type" : "WEB",
    "url" : "https://git.kernel.org/stable/c/20003fbb9174121b27bd1da6ebe61542ac4c327d"
  }, {
    "type" : "WEB",
    "url" : "https://git.kernel.org/stable/c/4cd8d755c7d4f515dd9abf483316aca2f1b7b0f3"
  }, {
    "type" : "WEB",
    "url" : "https://git.kernel.org/stable/c/60e6489f8e3b086bd1130ad4450a2c112e863791"
  }, {
    "type" : "WEB",
    "url" : "https://git.kernel.org/stable/c/db81ad20fd8aef7cc7d536c52ee5ea4c1f979128"
  }, {
    "type" : "WEB",
    "url" : "https://mohandacherir.github.io/Qdiv7/posts/unix_new_gc"
  } ],
  "database_specific" : {
    "cwe_ids" : [ ],
    "severity" : "HIGH",
    "github_reviewed" : false,
    "github_reviewed_at" : null,
    "nvd_published_at" : "2025-12-04T13:15:48Z"
  }
}