GHSA-G8MR-R59R-2XMQ

Vulnerability from github – Published: 2026-08-27 06:31 – Updated: 2026-08-27 06:31
VLAI
Details

In the Linux kernel, the following vulnerability has been resolved:

af_unix: Unlink scc_entry in unix_del_edge().

Kyle Zeng reported that GC could free a dead SCC partially.

The scenario is as follows:

1) Create two SCCs:

   X -.   A <-> B
   ^--'

2) Run the following concurrently:

  2-1) send() sk-B to sk-B from sk-X
  2-2) close() both A and B

At 2-1), there is a small window where unix_add_edges() publishes a new edge (B <-> B) to GC but its skb is not queued by skb_queue_tail().

If 2-2) completes before skb_queue_tail() and GC is triggered, it judges A <-> B as dead, but B is not freed because GC cannot collect the not-yet-queued skb holding the B <-> B edge.

   X -.   A <-> B -. This edge is visible
   ^--'         ^..'  but skb is not

This itself is not a problem since the next GC run will judge B as dead as well and free it finally.

   X -.   A <.> B -.
   ^--'         ^--'

However, X's SCC forces the next GC to call unix_walk_scc_fast(), and it iterates over A through B's scc_entry.

Let's unlink scc_entry before freeing the vertex in unix_del_edge().

Severity
7.8 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
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{
  "affected": [],
  "aliases": [
    "CVE-2026-80521"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-08-26T15:17:05Z",
    "severity": "HIGH"
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\naf_unix: Unlink scc_entry in unix_del_edge().\n\nKyle Zeng reported that GC could free a dead SCC partially.\n\nThe scenario is as follows:\n\n   1) Create two SCCs:\n\n       X -.   A \u003c-\u003e B\n       ^--\u0027\n\n   2) Run the following concurrently:\n\n      2-1) send() sk-B to sk-B from sk-X\n      2-2) close() both A and B\n\nAt 2-1), there is a small window where unix_add_edges()\npublishes a new edge (B \u003c-\u003e B) to GC but its skb is not queued\nby skb_queue_tail().\n\nIf 2-2) completes before skb_queue_tail() and GC is triggered,\nit judges A \u003c-\u003e B as dead, but B is not freed because GC cannot\ncollect the not-yet-queued skb holding the B \u003c-\u003e B edge.\n\n       X -.   A \u003c-\u003e B -. This edge is visible\n       ^--\u0027         ^..\u0027  but skb is not\n\nThis itself is not a problem since the next GC run will judge\nB as dead as well and free it finally.\n\n       X -.   A \u003c.\u003e B -.\n       ^--\u0027         ^--\u0027\n\nHowever, X\u0027s SCC forces the next GC to call unix_walk_scc_fast(),\nand it iterates over A through B\u0027s scc_entry.\n\nLet\u0027s unlink scc_entry before freeing the vertex in unix_del_edge().",
  "id": "GHSA-g8mr-r59r-2xmq",
  "modified": "2026-08-27T06:31:31Z",
  "published": "2026-08-27T06:31:31Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-80521"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/594d905195024b228c962627ae5ae7c17bd582a4"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/e3702470ced94fad74d71e2232f022d2eb752a6d"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
      "type": "CVSS_V3"
    }
  ]
}



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