CVE-2026-18036

published 2026-10-02

CVE-2026-18036: In Bouncy Castle for Java before 1.86, NTRU reduced secret values with the % operator in three helpers whose reference implementations are deliberately…

Priority P3 42 high 8.2 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

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.

Affected

1 ranges

Vendor	Product	Version range	Fixed in
legion_of_the_bouncy_castle_inc	bc-java	>= 1.73 < 1.86	1.86

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CWE-208