sctp: fix stream->outcnt underflow on duplicate RECONF responses

{
  "id": "6af5aa27557e45c390647ec67033f2f2fe251efeb9820eca05d24a9910f7f1ff",
  "url": "https://osv.dev/vulnerability/CVE-2026-89476",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "sctp: fix stream->outcnt underflow on duplicate RECONF responses",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: sctp: fix stream->outcnt underflow on duplicate RECONF responses A cached RECONF chunk may contain more than one request parameter. A duplicate response can therefore find and process the same ADD_OUT request again while another parameter is still outstanding, rolling back outcnt twice and possibly underflowing it. Track outstanding request types as bits and clear each bit after its first response. Later responses for the same request are then ignored.",
    "evidence": "osv:CVE-2026-89476",
    "products": [
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    "severity": "high",
    "structured": {
      "id": "CVE-2026-89476",
      "aliases": [
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          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
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      ],
      "modified": "2026-10-28T02:30:39.214457971Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/041f7df5a929d3e7435dd8387e8ea17f2d412b7d",
        "https://git.kernel.org/stable/c/092acd3c55a4077b00489064615d8d2d898daf91",
        "https://git.kernel.org/stable/c/2d867663c563e8009257b9edf9c8ec75d9bbf19a",
        "https://git.kernel.org/stable/c/3faf13aff243ca9f78d08b1a2956ef5a6fc77b6e",
        "https://git.kernel.org/stable/c/59f61c39cb99ee1737bd742a20094fe5653389bb",
        "https://git.kernel.org/stable/c/793519e343867ee9a3e84f6cac07f81f2aec7b5d",
        "https://git.kernel.org/stable/c/8320cbd81bc21a1ca6ebdf70ad610ebc5ef1bd68",
        "https://git.kernel.org/stable/c/d02a5794c3deedcb8476d017fcee2b7aaedab2e1",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/89xxx/CVE-2026-89476.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-89476",
        "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"
      ],
      "provider_metadata": {
        "cna_assigner": "Linux",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/89xxx/CVE-2026-89476.json"
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    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 506803,
  "published_at": "2026-09-11T19:43:33.193+00:00"
}