CVE-2026-18036 (GCVE-0-2026-18036)

Vulnerability from cvelistv5 – Published: 2026-10-02 07:54 – Updated: 2026-10-02 17:42
VLAI
Title
NTRU leaks private key information by reducing secret values with a non-constant-time integer division
Summary
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.
Severity
8.2 (High)
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
SSVC
Exploitation: none Automatable: no Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-10-02 17:42 UTC
CWE
  • CWE-208 - Observable Timing Discrepancy
Assigner
bcorg CNA under the mitre root
CNA scorecard B 84/100 over 74 records in the last 180 days details
References
Impacted products
Vendor Product Version CPE status
Legion of the Bouncy Castle Inc. BC-JAVA Affected: 1.73 , < 1.86 (maven)
guessed Create a notification for this product.
Credits
The Robusta team: Deepak Bhargavan Pillai, Anirban Chakraborty, Chitchanok Chuengsatiansup, Matthew Roughan, Peter Schwabe, and Yuval Yarom
Show details on NVD website
To clipboard 

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