---
id: CVE-2026-103603
title: >-
  Memory allocation with excessive size value in the HSS/LMS signature code
  (HssPublicKeyParameters, HssSignature) in Legion of the Bouncy Castle Inc
summary: >-
  Memory allocation with excessive size value in the HSS/LMS signature code
  (HssPublicKeyParameters, HssSignature) in Legion of the Bouncy Castle Inc.
  bc-csharp before 2.7.0 allows a remote unauthenticated attacker who can supply
  both an H…
severity: high
cvss: 8.7
cvssVector: 'CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N'
cwe:
  - CWE-789
vendor: Legion of the Bouncy Castle Inc.
product: BouncyCastle.Cryptography
affected:
  - BouncyCastle.Cryptography < 2.7.0
published: '2026-10-02'
updated: '2026-10-02'
sourceUpdated: '2026-10-02T08:17:00.837'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-103603'
references:
  - url: >-
      https://github.com/bcgit/bc-csharp/commit/f47ad47c7b5745b53d3f9ac711a5a419a272a5d7
    label: 91579145-5d7b-4cc5-b925-a0262ff19630
  - url: 'https://github.com/bcgit/bc-csharp/wiki/CVE-2026-103603'
    label: 91579145-5d7b-4cc5-b925-a0262ff19630
tags:
  - nvd
  - cve.org
cvssSource: cna
ingestedAt: '2026-10-02T08:14:06.226Z'
---

## Overview

Memory allocation with excessive size value in the HSS/LMS signature code (HssPublicKeyParameters, HssSignature) in Legion of the Bouncy Castle Inc. bc-csharp before 2.7.0 allows a remote unauthenticated attacker who can supply both an HSS public key and a signature to cause a denial of service through memory exhaustion via a public key encoding with an excessive level count, because the level count L read when parsing an HSS public key was not checked against the RFC 8554 maximum of 8, and signature parsing then allocated an array of L - 1 entries before reading any further signature data. A single verification can commit up to about 17 GB of memory or fail with an OutOfMemoryException.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.