{"id":"UBUNTU-CVE-2026-18036","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.","modified":"2026-10-05T13:04:12.065719695Z","published":"2026-10-05T00:00:00Z","upstream":["CVE-2026-18036"],"references":[{"type":"REPORT","url":"https://ubuntu.com/security/CVE-2026-18036"},{"type":"REPORT","url":"https://www.cve.org/CVERecord?id=CVE-2026-18036"},{"type":"REPORT","url":"https://github.com/bcgit/bc-java/wiki/CVE%E2%80%902026%E2%80%9018036"},{"type":"REPORT","url":"https://github.com/bcgit/bc-java/commit/9c9ad88b6003bb6230d2434bd892cc1e95b294e4"}],"affected":[{"package":{"name":"bouncycastle","ecosystem":"Ubuntu:Pro:16.04:LTS","purl":"pkg:deb/ubuntu/bouncycastle?arch=source&distro=esm-apps%2Fxenial"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.49+dfsg-3ubuntu1","1.51-4ubuntu1","1.51-4ubuntu1+esm1"],"ecosystem_specific":{"binaries":[{"binary_name":"libbcmail-java","binary_version":"1.51-4ubuntu1+esm1"},{"binary_version":"1.51-4ubuntu1+esm1","binary_name":"libbcpg-java"},{"binary_version":"1.51-4ubuntu1+esm1","binary_name":"libbcpkix-java"},{"binary_name":"libbcprov-java","binary_version":"1.51-4ubuntu1+esm1"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-18036.json"}},{"package":{"name":"bouncycastle","ecosystem":"Ubuntu:Pro:18.04:LTS","purl":"pkg:deb/ubuntu/bouncycastle?arch=source&distro=esm-apps%2Fbionic"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.57-1","1.58-1","1.59-1","1.59-1ubuntu0.1~esm1"],"ecosystem_specific":{"binaries":[{"binary_name":"libbcmail-java","binary_version":"1.59-1ubuntu0.1~esm1"},{"binary_name":"libbcpg-java","binary_version":"1.59-1ubuntu0.1~esm1"},{"binary_name":"libbcpkix-java","binary_version":"1.59-1ubuntu0.1~esm1"},{"binary_name":"libbcprov-java","binary_version":"1.59-1ubuntu0.1~esm1"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-18036.json"}},{"package":{"name":"bouncycastle","ecosystem":"Ubuntu:Pro:20.04:LTS","purl":"pkg:deb/ubuntu/bouncycastle?arch=source&distro=esm-apps%2Ffocal"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.61-1","1.61-1ubuntu0.1~esm1"],"ecosystem_specific":{"binaries":[{"binary_name":"libbcmail-java","binary_version":"1.61-1ubuntu0.1~esm1"},{"binary_name":"libbcpg-java","binary_version":"1.61-1ubuntu0.1~esm1"},{"binary_name":"libbcpkix-java","binary_version":"1.61-1ubuntu0.1~esm1"},{"binary_name":"libbcprov-java","binary_version":"1.61-1ubuntu0.1~esm1"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-18036.json"}},{"package":{"name":"bouncycastle","ecosystem":"Ubuntu:Pro:22.04:LTS","purl":"pkg:deb/ubuntu/bouncycastle?arch=source&distro=esm-apps%2Fjammy"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.68-2","1.68-4","1.68-5","1.68-5ubuntu0.1~esm1"],"ecosystem_specific":{"binaries":[{"binary_name":"libbcmail-java","binary_version":"1.68-5ubuntu0.1~esm1"},{"binary_version":"1.68-5ubuntu0.1~esm1","binary_name":"libbcpg-java"},{"binary_name":"libbcpkix-java","binary_version":"1.68-5ubuntu0.1~esm1"},{"binary_name":"libbcprov-java","binary_version":"1.68-5ubuntu0.1~esm1"},{"binary_name":"libbctls-java","binary_version":"1.68-5ubuntu0.1~esm1"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-18036.json"}},{"package":{"name":"bouncycastle","ecosystem":"Ubuntu:Pro:24.04:LTS","purl":"pkg:deb/ubuntu/bouncycastle?arch=source&distro=esm-apps%2Fnoble"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.72-2","1.77-1","1.77-1ubuntu0.1~esm1"],"ecosystem_specific":{"binaries":[{"binary_version":"1.77-1ubuntu0.1~esm1","binary_name":"libbcjmail-java"},{"binary_name":"libbcmail-java","binary_version":"1.77-1ubuntu0.1~esm1"},{"binary_name":"libbcpg-java","binary_version":"1.77-1ubuntu0.1~esm1"},{"binary_version":"1.77-1ubuntu0.1~esm1","binary_name":"libbcpkix-java"},{"binary_version":"1.77-1ubuntu0.1~esm1","binary_name":"libbcprov-java"},{"binary_name":"libbctls-java","binary_version":"1.77-1ubuntu0.1~esm1"},{"binary_name":"libbcutil-java","binary_version":"1.77-1ubuntu0.1~esm1"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-18036.json"}},{"package":{"name":"bouncycastle","ecosystem":"Ubuntu:26.04:LTS","purl":"pkg:deb/ubuntu/bouncycastle?arch=source&distro=resolute"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.80-3"],"ecosystem_specific":{"binaries":[{"binary_name":"libbcjmail-java","binary_version":"1.80-3"},{"binary_name":"libbcmail-java","binary_version":"1.80-3"},{"binary_name":"libbcpg-java","binary_version":"1.80-3"},{"binary_name":"libbcpkix-java","binary_version":"1.80-3"},{"binary_name":"libbcprov-java","binary_version":"1.80-3"},{"binary_version":"1.80-3","binary_name":"l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