CVE-2026-18040

In Bouncy Castle for Java before 1.86, HQC leaked secret-derived data through two side channels: its GF(2^8) arithmetic used lookup tables indexed by field elements, making the cache line touched a function of the operand, and its fixed-weight support sampler left its duplicate scan as soon as a collision was found and stored accepted positions at a secret index. Both run on secret inputs during encapsulation and decapsulation, and the sampler re-expands the secret key from its seed on every decapsulation, so an attacker able to observe cache behaviour or decapsulation timing can recover information about the HQC private key. The field arithmetic is now table-free and the sampler branch-free within a batch of candidates, with output and randomness consumption unchanged.

CVSS

No CVSS.

References

Link	Resource
https://github.com/bcgit/bc-java/commit/283acd81048ec9e951032525279d3b58aaf0bb03
https://github.com/bcgit/bc-java/wiki/CVE%E2%80%902026%E2%80%9018040

Configurations

No configuration.

History

03 Oct 2026, 09:17

Type	Values Removed	Values Added
New CVE

Information

Published : 2026-10-03 09:17

Updated : 2026-10-06 14:49

NVD link : CVE-2026-18040

Mitre link : CVE-2026-18040

CVE.ORG link : CVE-2026-18040

JSON object : View

Products Affected

No product.

CWE

CWE-208

Observable Timing Discrepancy

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