---
id: CVE-2026-63566
title: >-
  Memory allocation with excessive size value in the DTLS handshake reassembly
  (DtlsReliableHandshake, DtlsReassembler) in Legion of the Bouncy Castle Inc
summary: >-
  Memory allocation with excessive size value in the DTLS handshake reassembly
  (DtlsReliableHandshake, DtlsReassembler) in Legion of the Bouncy Castle Inc.
  bc-csharp before 2.7.0 allows a remote unauthenticated DTLS peer to cause a
  denial …
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: '2026-10-02T07:16:36.973'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-63566'
references:
  - url: >-
      https://github.com/bcgit/bc-csharp/commit/212d06474166d5e85be72c2dd4898313aa5dd5f3
    label: 91579145-5d7b-4cc5-b925-a0262ff19630
  - url: >-
      https://github.com/bcgit/bc-csharp/commit/99afef612458f70f28e7824a09719bfc3a169bda
    label: 91579145-5d7b-4cc5-b925-a0262ff19630
  - url: 'https://github.com/bcgit/bc-csharp/wiki/CVE-2026-63566'
    label: 91579145-5d7b-4cc5-b925-a0262ff19630
tags:
  - nvd
  - cve.org
cvssSource: cna
ingestedAt: '2026-10-02T07:13:06.669Z'
---

## Overview

Memory allocation with excessive size value in the DTLS handshake reassembly (DtlsReliableHandshake, DtlsReassembler) in Legion of the Bouncy Castle Inc. bc-csharp before 2.7.0 allows a remote unauthenticated DTLS peer to cause a denial of service through memory exhaustion via crafted handshake message fragments, because the reassembly buffer for each incoming handshake message was allocated at the 24-bit length declared in the fragment header, without the check against the peer's maximum handshake message size that TLS already applied. A fragment carrying no payload can force an allocation of almost 16 MB, for each of up to 16 pending messages per handshake, before the handshake is authenticated. DTLS servers and DTLS clients are both affected; TLS is not.

## Remediation

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