{
  "affected": [
    {
      "ranges": [
        {
          "database_specific": {
            "extracted_events": [
              {
                "introduced": "1.73"
              },
              {
                "fixed": "1.86"
              }
            ],
            "source": "AFFECTED_FIELD"
          },
          "events": [
            {
              "introduced": "9032821b326fba9fec7528899dfffa79f9f19aef"
            },
            {
              "fixed": "eacda831fbe15b272933e40841d8b0827b556fae"
            }
          ],
          "repo": "https://github.com/bcgit/bc-java",
          "type": "GIT"
        }
      ]
    }
  ],
  "database_specific": {
    "cna_assigner": "bcorg",
    "cwe_ids": [
      "CWE-208"
    ],
    "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/18xxx/CVE-2026-18036.json"
  },
  "details": "In Bouncy Castle for Java before 1.86, NTRU reduced secret values with the % operator in three helpers whose reference implementations are deliberately division-free, so each reduction was carried out by an integer division whose latency depends on the secret operand. Polynomial.modQ divided by a variable divisor, which a compiler cannot strength-reduce to a multiply the way it can a constant one, so it emitted a division on every call including on the decapsulation path where the dividend derives from the private key; Polynomial.mod3 and NTRUSampling.mod3 divided the secret key polynomials f and g during key generation, the message polynomials r and m during encapsulation, and coefficients recovered during decapsulation. An attacker able to measure that timing can recover information about the NTRU private key. modQ now masks, which is exact because q is always a power of two, and mod3 uses the reference implementation's division-free fold and select; the results are unchanged.",
  "id": "CVE-2026-18036",
  "modified": "2026-10-04T02:30:16.677519266Z",
  "published": "2026-10-02T07:54:16.063Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://www.bouncycastle.org/download/bouncy-castle-java/"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/18xxx/CVE-2026-18036.json"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/bcgit/bc-java/wiki/CVE%E2%80%902026%E2%80%9018036"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-18036"
    },
    {
      "type": "FIX",
      "url": "https://github.com/bcgit/bc-java/commit/9c9ad88b6003bb6230d2434bd892cc1e95b294e4"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/bcgit/bc-java"
    }
  ],
  "schema_version": "1.9.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/U:Amber",
      "type": "CVSS_V4"
    }
  ],
  "summary": "NTRU leaks private key information by reducing secret values with a non-constant-time integer division"
}