Use-After-Free and Double Free in IntoIter::drop When Element Drop Panics

{
  "id": "7801f58d2a16fe9ae7f4c5ce254464a93f6c5a0cfd3a12397794628013c8c0a4",
  "url": "https://osv.dev/vulnerability/RUSTSEC-2026-0103",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "Use-After-Free and Double Free in IntoIter::drop When Element Drop Panics",
    "summary": "A Double Free / Use-After-Free (UAF) vulnerability has been identified in the `IntoIter::drop` and `ThinVec::clear` implementations of the `thin-vec` crate. Both vulnerabilities share the same root cause and can trigger memory corruption using only safe Rust code - no unsafe blocks required. Undefined Behavior has been confirmed via Miri and AddressSanitizer (ASAN). ## Details When a **panic occurs** during sequential element deallocation, the subsequent length cleanup code (`set_len(0)`) is never executed. During stack unwinding, the container is dropped again, causing already-freed memory to be re-freed (Double Free / UAF). ### Vulnerability 1 - `IntoIter::drop` `IntoIter::drop` transfers ownership of the internal buffer via `mem::replace`, then sequentially frees elements via `ptr::drop_in_place`. If a panic occurs during element deallocation, `set_len_non_singleton(0)` is never reached. During unwinding, `vec` is dropped again, re-freeing already-freed elements. The standard library's `std::vec::IntoIter` prevents this with a **DropGuard pattern**, but thin-vec lacks this defense. ### PoC ```rust use thin_vec::ThinVec; struct PanicBomb(String); impl Drop for PanicBomb { fn drop(&mut self) { if self.0 == \"panic\" { panic!(\"panic!\"); } println!(\"Dropping: {}\", self.0); } } fn main() { let mut v = ThinVec::new(); v.push(PanicBomb(String::from(\"normal1\"))); v.push(PanicBomb(String::from(\"panic\"))); // trigger element v.push(PanicBomb(String::from(\"normal2\"))); let mut iter = v",
    "evidence": "osv:RUSTSEC-2026-0103",
    "products": [
      {
        "name": {
          "value": "thin-vec",
          "evidence": "/affected/0/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "0.2.16",
            "evidence": "/affected/0/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "high",
    "structured": {
      "id": "RUSTSEC-2026-0103",
      "aliases": [
        "CVE-2026-6654",
        "GHSA-xphw-cqx3-667j",
        "RUSTSEC-2026-0103"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "type": "SEMVER",
              "events": [
                {
                  "introduced": "0.0.0-0"
                },
                {
                  "fixed": "0.2.16"
                }
              ]
            }
          ],
          "package": {
            "name": "thin-vec",
            "purl": "pkg:cargo/thin-vec",
            "ecosystem": "crates.io"
          },
          "database_specific": {
            "cvss": "CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H",
            "source": "https://github.com/rustsec/advisory-db/blob/osv/crates/RUSTSEC-2026-0103.json",
            "categories": [
              "code-execution",
              "memory-corruption",
              "memory-exposure"
            ],
            "informational": null
          },
          "ecosystem_specific": {
            "affects": {
              "os": [],
              "arch": [],
              "functions": []
            },
            "affected_functions": null
          }
        }
      ],
      "modified": "2026-10-12T18:00:08.228043402Z",
      "provider": "osv",
      "references": [
        "https://crates.io/crates/thin-vec",
        "https://rustsec.org/advisories/RUSTSEC-2026-0103.html",
        "https://github.com/mozilla/thin-vec/commit/df64748355222525c344ecd9d2c9f59a662e1678"
      ],
      "provider_metadata": {
        "license": "CC0-1.0"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-6654",
        "evidence": "/aliases"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 306383,
  "published_at": "2026-04-14T12:00:00+00:00"
}