pymonocypher: Potential heap buffer overflow on nb_blocks in argon2i_32 when provided buffer is too small

{
  "id": "4910a07f14616cb239b768770c683a8de17bcd3e8db90ed378deb416fafc021d",
  "url": "https://osv.dev/vulnerability/CVE-2026-53720",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "pymonocypher: Potential heap buffer overflow on nb_blocks in argon2i_32 when provided buffer is too small",
    "summary": "pymonocypher uses cython to wrap the Monocypher C library. Prior to version 4.0.2.8, the argon2i_32 implementation does not check the nb_blocks size. If the caller does not provide a sufficiently large buffer based on the API contract, then argon2i_32 will write past the end of the buffer and possibly corrupt the heap. This issue has been patched in version 4.0.2.8.",
    "evidence": "osv:CVE-2026-53720",
    "products": [],
    "severity": "medium",
    "structured": {
      "id": "CVE-2026-53720",
      "aliases": [
        "CVE-2026-53720",
        "GHSA-8f95-v3jq-cj86",
        "PYSEC-2026-3000"
      ],
      "metrics": [
        {
          "type": "CVSS_V4",
          "score": "CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:L/SC:N/SI:N/SA:N"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/jetperch/pymonocypher",
              "type": "GIT",
              "events": [
                {
                  "introduced": "0"
                },
                {
                  "fixed": "896a6bdd527e1cbf351ebbdd2f513296b49a7f95"
                },
                {
                  "fixed": "90ff5b13b13b5673c372e188f482d8c172e6ab86"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "range": [
                      {
                        "introduced": "0"
                      },
                      {
                        "fixed": "4.0.2.8"
                      }
                    ],
                    "source": "AFFECTED_FIELD",
                    "strategy": "StringRangeExpression"
                  },
                  {
                    "range": [
                      {
                        "fixed": "90ff5b13b13b5673c372e188f482d8c172e6ab86"
                      }
                    ],
                    "source": "REFERENCES_COMMIT"
                  },
                  {
                    "range": [
                      {
                        "fixed": "896a6bdd527e1cbf351ebbdd2f513296b49a7f95"
                      }
                    ],
                    "source": "REFERENCES_TAG",
                    "original_tag": "v4.0.2.8"
                  }
                ]
              }
            }
          ],
          "versions": [
            "v4.0.2.7",
            "v4.0.2.6",
            "v4.0.2.5",
            "v4.0.2.4",
            "v4.0.2.3",
            "v3.1.3.2",
            "v4.0.2.2",
            "v4.0.2.1",
            "v3.1.3.1",
            "v3.1.0.0",
            "v0.1.4",
            "v0.1.3"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-53720.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:27.395908414Z",
      "provider": "osv",
      "references": [
        "https://github.com/jetperch/pymonocypher/releases/tag/v4.0.2.8",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/53xxx/CVE-2026-53720.json",
        "https://github.com/jetperch/pymonocypher/security/advisories/GHSA-8f95-v3jq-cj86",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-53720",
        "https://github.com/jetperch/pymonocypher/commit/90ff5b13b13b5673c372e188f482d8c172e6ab86"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-122",
          "CWE-1284",
          "CWE-787"
        ],
        "cna_assigner": "GitHub_M",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/53xxx/CVE-2026-53720.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-53720",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 493865,
  "published_at": "2026-09-03T15:30:06.69+00:00"
}