{"id":"CVE-2026-18036","revision":null,"records":[{"revision":"aef02fd4d3ef4578a12c07a4f962edde","observedAt":"2026-10-23T15:48:27.903+00:00","statement":{"source":"cve-program","id":"CVE-2026-18036","aliases":[],"title":"NTRU leaks private key information by reducing secret values with a non-constant-time integer division","description":"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.","state":0,"publishedAt":"2026-10-02T07:54:16.063+00:00","modifiedAt":"2026-10-02T17:42:56.393+00:00","affected":[{"ecosystem":"https://www.bouncycastle.org/download/bouncy-castle-java/","name":"bcprov","ranges":[],"versions":[],"rawVersionEvidence":"{\n                    \"vendor\": \"Legion of the Bouncy Castle Inc.\",\n                    \"product\": \"BC-JAVA\",\n                    \"platforms\": [\n                        \"all\"\n                    ],\n                    \"collectionURL\": \"https://www.bouncycastle.org/download/bouncy-castle-java/\",\n                    \"packageName\": \"bcprov\",\n                    \"repo\": \"https://github.com/bcgit/bc-java\",\n                    \"packageURL\": \"pkg:maven/org.bouncycastle/bcprov-jdk18on\",\n                    \"modules\": [\n                        \"core\"\n                    ],\n                    \"programFiles\": [\n                        \"Polynomial\",\n                        \"NTRUSampling\"\n                    ],\n                    \"versions\": [\n                        {\n                            \"status\": \"affected\",\n                            \"version\": \"1.73\",\n                            \"lessThan\": \"1.86\",\n                            \"versionType\": \"maven\"\n                        }\n                    ],\n                    \"defaultStatus\": \"unaffected\"\n                }"}],"metrics":[{"system":"CVSS 4.0","vector":"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","score":8.2,"severity":"HIGH"}],"references":["https://github.com/bcgit/bc-java/wiki/CVE%E2%80%902026%E2%80%9018036","https://github.com/bcgit/bc-java/commit/9c9ad88b6003bb6230d2434bd892cc1e95b294e4"],"sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-18036","license":"CVE Program Terms of Use","key":"cve-program:CVE-2026-18036","identifiers":["CVE-2026-18036"]},"retained":false,"historicalAffected":[]}],"coverage":[{"source":"cisa-kev:global","scope":"Complete CISA KEV catalog; all vendors. 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