Use-after-free from a comparator that answers inconsistently

{
  "id": "46146287cf0d4031094acf0ae649dfcd2f1e6da1689df6e36dded1becaea3130",
  "url": "https://osv.dev/vulnerability/RUSTSEC-2026-0409",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "Use-after-free from a comparator that answers inconsistently",
    "summary": "`OrderedSkipList`, `SkipSet` and `SkipMap` can free a node that is still linked when a `Comparator` or `Ord` implementation gives different answers for the same pair of values during one mutating call. A later call reads the freed memory (CWE-416). A safe `impl Ord` with the default comparator is enough to reach it. The mutating traversals record a precursor at each level: the last node whose link points at a node comparing not-`Less` than the target. The splice code assumes every recorded precursor's link points at or past the final position. If a later comparison reports one of those nodes as `Less`, the walk steps past it and the assumption breaks. Removals such as `take_first`, `take` and `remove` then rewire the wrong link and free the target while its real predecessor still points at it. `insert` builds crossed links and wrong skip distances from the same precursors. A comparator that is a pure function of its two arguments cannot trigger this, even if it is not transitive. The trigger is a stateful or non-deterministic implementation, for example one that reads a counter, a cache, a clock or a random source. The flaw was corrected in 1.3.0. The mutating traversals track the link target of the lowest recorded precursor and panic with \"comparator does not implement a total order\" when a `Less` answer contradicts an earlier one. Every splice site also checks its precursors before the first write. Each detected contradiction panics before any link, value or length changes,",
    "evidence": "osv:RUSTSEC-2026-0409",
    "products": [
      {
        "name": {
          "value": "skiplist",
          "evidence": "/affected/0/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "1.3.0",
            "evidence": "/affected/0/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "medium",
    "structured": {
      "id": "RUSTSEC-2026-0409",
      "aliases": [
        "GHSA-cc53-p78w-23w9",
        "RUSTSEC-2026-0409"
      ],
      "metrics": [
        {
          "type": "CVSS_V4",
          "score": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:L/VA:L/SC:N/SI:N/SA:N"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "type": "SEMVER",
              "events": [
                {
                  "introduced": "0.0.0-0"
                },
                {
                  "fixed": "1.3.0"
                }
              ]
            }
          ],
          "package": {
            "name": "skiplist",
            "purl": "pkg:cargo/skiplist",
            "ecosystem": "crates.io"
          },
          "database_specific": {
            "cvss": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:L/VA:L/SC:N/SI:N/SA:N",
            "source": "https://github.com/rustsec/advisory-db/blob/osv/crates/RUSTSEC-2026-0409.json",
            "categories": [
              "memory-corruption"
            ],
            "informational": null
          },
          "ecosystem_specific": {
            "affects": {
              "os": [],
              "arch": [],
              "functions": []
            },
            "affected_functions": null
          }
        }
      ],
      "modified": "2026-10-26T14:00:04.241377560Z",
      "provider": "osv",
      "references": [
        "https://crates.io/crates/skiplist",
        "https://rustsec.org/advisories/RUSTSEC-2026-0409.html",
        "https://github.com/JP-Ellis/rust-skiplist/issues/401",
        "https://github.com/JP-Ellis/rust-skiplist/pull/407"
      ],
      "provider_metadata": {
        "license": "CC0-1.0"
      }
    },
    "related_cves": [],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 454184,
  "published_at": "2026-10-24T12:00:00+00:00"
}