Heap overflow via truncated base64 encoding of binary fields in length-limited JSON output

{
  "id": "02d628665eaf533194ff330d4060bed75847d83f4a5247bfee34010e5b42ce25",
  "url": "https://osv.dev/vulnerability/CVE-2026-84969",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "Heap overflow via truncated base64 encoding of binary fields in length-limited JSON output",
    "summary": "A memory-handling error in the BSON-to-JSON conversion helpers of the MongoDB C Driver can write a small number of bytes past the end of a heap buffer when a binary field is encoded and the output is cut short at a caller-configured length limit. A party who supplies the document content, with no privileges on the application that links the driver, may cause a small amount of data outside the intended buffer to be altered.",
    "evidence": "osv:CVE-2026-84969",
    "products": [],
    "severity": "medium",
    "structured": {
      "id": "CVE-2026-84969",
      "aliases": [
        "CVE-2026-84969"
      ],
      "metrics": [
        {
          "type": "CVSS_V4",
          "score": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/mongodb/mongo-c-driver",
              "type": "GIT",
              "events": [
                {
                  "introduced": "be3955bb98ecabeb8e2873804f3345250e9bff60"
                },
                {
                  "fixed": "f64476433230847fb0f43afaeb7be048eb817f8b"
                },
                {
                  "introduced": "67817df0a9ed11b07e457477e6db1384da9421c4"
                },
                {
                  "fixed": "52ffca1e649b597c51162b5b3b37f057b73b059d"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "cpe": "cpe:2.3:a:mongodb:c_driver:*:*:*:*:*:mongodb:*:*",
                    "range": [
                      {
                        "introduced": "1.30.0"
                      },
                      {
                        "fixed": "1.30.9"
                      }
                    ],
                    "source": "CPE_RANGE"
                  },
                  {
                    "cpe": "cpe:2.3:a:mongodb:c_driver:*:*:*:*:*:mongodb:*:*",
                    "range": [
                      {
                        "introduced": "2.0.0"
                      },
                      {
                        "fixed": "2.5.2"
                      }
                    ],
                    "source": "CPE_RANGE"
                  }
                ]
              }
            }
          ],
          "versions": [
            "1.30.8",
            "1.30.7",
            "1.30.6",
            "1.30.5",
            "1.30.4",
            "1.30.3",
            "1.30.2",
            "1.30.1",
            "1.30.0"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-84969.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:37.415384750Z",
      "provider": "osv",
      "references": [
        "https://jira.mongodb.org/browse/CDRIVER-6410",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/84xxx/CVE-2026-84969.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-84969"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-787"
        ],
        "cna_assigner": "mongodb",
        "unresolved_ranges": [
          {
            "extracted_events": [
              {
                "range": [
                  {
                    "introduced": "1.30.0"
                  },
                  {
                    "fixed": "1.30.9"
                  },
                  {
                    "introduced": "2.0.0"
                  },
                  {
                    "fixed": "2.5.2"
                  }
                ],
                "source": "AFFECTED_FIELD",
                "strategy": "StandardRange"
              }
            ]
          }
        ],
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/84xxx/CVE-2026-84969.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-84969",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 504889,
  "published_at": "2026-09-03T14:59:01.427+00:00"
}