{"dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": {"cveId": "CVE-2026-18036", "assignerOrgId": "91579145-5d7b-4cc5-b925-a0262ff19630", "state": "PUBLISHED", "assignerShortName": "bcorg", "dateReserved": "2026-07-28T08:28:40.900Z", "datePublished": "2026-10-02T07:54:16.063Z", "dateUpdated": "2026-10-02T07:54:16.063Z"}, "containers": {"cna": {"providerMetadata": {"orgId": "91579145-5d7b-4cc5-b925-a0262ff19630", "shortName": "bcorg", "dateUpdated": "2026-10-02T07:54:16.063Z"}, "title": "NTRU leaks private key information by reducing secret values with a non-constant-time integer division", "problemTypes": [{"descriptions": [{"lang": "en", "cweId": "CWE-208", "description": "CWE-208 Observable Timing Discrepancy", "type": "CWE"}]}], "affected": [{"vendor": "Legion of the Bouncy Castle Inc.", "product": "BC-JAVA", "platforms": ["all"], "collectionURL": "https://www.bouncycastle.org/download/bouncy-castle-java/", "packageName": "bcprov", "repo": "https://github.com/bcgit/bc-java", "packageURL": "pkg:maven/org.bouncycastle/bcprov-jdk18on", "modules": ["core"], "programFiles": ["Polynomial", "NTRUSampling"], "versions": [{"status": "affected", "version": "1.73", "lessThan": "1.86", "versionType": "maven"}], "defaultStatus": "unaffected"}], "descriptions": [{"lang": "en", "value": "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.", "supportingMedia": [{"type": "text/html", "base64": false, "value": "<p>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.</p>"}]}], "references": [{"url": "https://github.com/bcgit/bc-java/wiki/CVE%E2%80%902026%E2%80%9018036", "tags": ["vendor-advisory"]}, {"url": "https://github.com/bcgit/bc-java/commit/9c9ad88b6003bb6230d2434bd892cc1e95b294e4", "tags": ["patch"]}], "metrics": [{"format": "CVSS", "scenarios": [{"lang": "en", "value": "GENERAL"}], "cvssV4_0": {"attackVector": "NETWORK", "attackComplexity": "HIGH", "attackRequirements": "PRESENT", "privilegesRequired": "NONE", "userInteraction": "NONE", "vulnConfidentialityImpact": "HIGH", "subConfidentialityImpact": "NONE", "vulnIntegrityImpact": "NONE", "subIntegrityImpact": "NONE", "vulnAvailabilityImpact": "NONE", "subAvailabilityImpact": "NONE", "exploitMaturity": "NOT_DEFINED", "Safety": "NOT_DEFINED", "Automatable": "NOT_DEFINED", "Recovery": "NOT_DEFINED", "valueDensity": "NOT_DEFINED", "vulnerabilityResponseEffort": "NOT_DEFINED", "providerUrgency": "AMBER", "version": "4.0", "baseSeverity": "HIGH", "baseScore": 8.2, "vectorString": "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"}}], "credits": [{"lang": "en", "value": "The Robusta team: Deepak Bhargavan Pillai, Anirban Chakraborty, Chitchanok Chuengsatiansup, Matthew Roughan, Peter Schwabe, and Yuval Yarom", "type": "reporter"}], "source": {"discovery": "EXTERNAL"}, "x_generator": {"engine": "bc release-notes template"}}}}

{}

{"affected": [{"affectedData": [{"collectionURL": "https://www.bouncycastle.org/download/bouncy-castle-java/", "defaultStatus": "unaffected", "modules": ["core"], "packageName": "bcprov", "packageURL": "pkg:maven/org.bouncycastle/bcprov-jdk18on", "platforms": ["all"], "product": "BC-JAVA", "programFiles": ["Polynomial", "NTRUSampling"], "repo": "https://github.com/bcgit/bc-java", "vendor": "Legion of the Bouncy Castle Inc.", "versions": [{"lessThan": "1.86", "status": "affected", "version": "1.73", "versionType": "maven"}]}], "source": "91579145-5d7b-4cc5-b925-a0262ff19630"}], "cveTags": [], "descriptions": [{"lang": "en", "value": "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", "lastModified": "2026-10-02T08:17:01.660", "metrics": {"cvssMetricV40": [{"cvssData": {"Automatable": "NOT_DEFINED", "Recovery": "NOT_DEFINED", "Safety": "NOT_DEFINED", "attackComplexity": "HIGH", "attackRequirements": "PRESENT", "attackVector": "NETWORK", "availabilityRequirement": "NOT_DEFINED", "baseScore": 8.2, "baseSeverity": "HIGH", "confidentialityRequirement": "NOT_DEFINED", "exploitMaturity": "NOT_DEFINED", "integrityRequirement": "NOT_DEFINED", "modifiedAttackComplexity": "NOT_DEFINED", "modifiedAttackRequirements": "NOT_DEFINED", "modifiedAttackVector": "NOT_DEFINED", "modifiedPrivilegesRequired": "NOT_DEFINED", "modifiedSubAvailabilityImpact": "NOT_DEFINED", "modifiedSubConfidentialityImpact": "NOT_DEFINED", "modifiedSubIntegrityImpact": "NOT_DEFINED", "modifiedUserInteraction": "NOT_DEFINED", "modifiedVulnAvailabilityImpact": "NOT_DEFINED", "modifiedVulnConfidentialityImpact": "NOT_DEFINED", "modifiedVulnIntegrityImpact": "NOT_DEFINED", "privilegesRequired": "NONE", "providerUrgency": "AMBER", "subAvailabilityImpact": "NONE", "subConfidentialityImpact": "NONE", "subIntegrityImpact": "NONE", "userInteraction": "NONE", "valueDensity": "NOT_DEFINED", "vectorString": "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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:Amber", "version": "4.0", "vulnAvailabilityImpact": "NONE", "vulnConfidentialityImpact": "HIGH", "vulnIntegrityImpact": "NONE", "vulnerabilityResponseEffort": "NOT_DEFINED"}, "source": "91579145-5d7b-4cc5-b925-a0262ff19630", "type": "Secondary"}]}, "published": "2026-10-02T08:17:01.660", "references": [{"source": "91579145-5d7b-4cc5-b925-a0262ff19630", "url": "https://github.com/bcgit/bc-java/commit/9c9ad88b6003bb6230d2434bd892cc1e95b294e4"}, {"source": "91579145-5d7b-4cc5-b925-a0262ff19630", "url": "https://github.com/bcgit/bc-java/wiki/CVE%E2%80%902026%E2%80%9018036"}], "sourceIdentifier": "91579145-5d7b-4cc5-b925-a0262ff19630", "vulnStatus": "Received", "weaknesses": [{"description": [{"lang": "en", "value": "CWE-208"}], "source": "91579145-5d7b-4cc5-b925-a0262ff19630", "type": "Secondary"}]}

{}

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