webtransport-go CloseWithError can block indefinitely

{
  "id": "3fbebb35f6125529e2937d8cc7fb249ebd025d74b98916ae80086b3d4163861c",
  "url": "https://osv.dev/vulnerability/CVE-2026-21435",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "webtransport-go CloseWithError can block indefinitely",
    "summary": "webtransport-go is an implementation of the WebTransport protocol. Prior to v0.10.0, an attacker can cause a denial of service in webtransport-go by preventing or indefinitely delaying WebTransport session closure. A malicious peer can withhold QUIC flow control credit on the CONNECT stream, blocking transmission of the WT_CLOSE_SESSION capsule and causing the close operation to hang. This vulnerability is fixed in v0.10.0.",
    "evidence": "osv:CVE-2026-21435",
    "products": [],
    "severity": "medium",
    "structured": {
      "id": "CVE-2026-21435",
      "aliases": [
        "CVE-2026-21435",
        "GHSA-px4r-g4p3-hhqv",
        "GO-2026-4488"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/quic-go/webtransport-go",
              "type": "GIT",
              "events": [
                {
                  "introduced": "0"
                },
                {
                  "fixed": "9d448b125754f4c83064afb2c586221214e55eec"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "range": [
                      {
                        "introduced": "0"
                      },
                      {
                        "fixed": "0.10.0"
                      }
                    ],
                    "source": "AFFECTED_FIELD",
                    "strategy": "StringRangeExpression"
                  },
                  {
                    "range": [
                      {
                        "fixed": "9d448b125754f4c83064afb2c586221214e55eec"
                      }
                    ],
                    "source": "REFERENCES_TAG",
                    "original_tag": "v0.10.0"
                  },
                  {
                    "cpe": "cpe:2.3:a:quic-go:webtransport-go:*:*:*:*:*:go:*:*",
                    "range": [
                      {
                        "introduced": "0"
                      },
                      {
                        "fixed": "0.10.0"
                      }
                    ],
                    "source": "CPE_RANGE"
                  }
                ]
              }
            }
          ],
          "versions": [
            "v0.9.0",
            "v0.8.0",
            "v0.7.0",
            "v0.6.0",
            "v0.5.3",
            "v0.5.2",
            "v0.5.1",
            "v0.5.0",
            "v0.4.3",
            "v0.4.2",
            "v0.4.1",
            "v0.4.0",
            "v0.3.0",
            "v0.2.0",
            "v0.1.0"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-21435.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:49.636063092Z",
      "provider": "osv",
      "references": [
        "https://github.com/quic-go/webtransport-go/releases/tag/v0.10.0",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/21xxx/CVE-2026-21435.json",
        "https://github.com/quic-go/webtransport-go/security/advisories/GHSA-px4r-g4p3-hhqv",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-21435"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-400"
        ],
        "cna_assigner": "GitHub_M",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/21xxx/CVE-2026-21435.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-21435",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 517936,
  "published_at": "2026-02-12T18:22:58.098+00:00"
}