Legion of the Bouncy Castle bc-csharp up to 2.6.x DTLS Handshake Reassembly allocation of resources

Summaryinfo

A vulnerability described as problematic has been identified in Legion of the Bouncy Castle bc-csharp up to 2.6.x. This affects an unknown function of the component DTLS Handshake Reassembly. Such manipulation leads to allocation of resources. This vulnerability is referenced as CVE-2026-63566. It is possible to launch the attack remotely. No exploit is available. Upgrading the affected component is recommended.

Detailsinfo

A vulnerability was found in Legion of the Bouncy Castle bc-csharp up to 2.6.x and classified as problematic. Affected by this issue is an unknown code block of the component DTLS Handshake Reassembly. The manipulation with an unknown input leads to a allocation of resources vulnerability. Using CWE to declare the problem leads to CWE-770. The product allocates a reusable resource or group of resources on behalf of an actor without imposing any restrictions on the size or number of resources that can be allocated, in violation of the intended security policy for that actor. Impacted is availability. CVE summarizes:

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.

The advisory is available at github.com. This vulnerability is handled as CVE-2026-63566 since 07/17/2026. The exploitation is known to be easy. The attack may be launched remotely. No form of authentication is required for exploitation. The technical details are unknown and an exploit is not available. This vulnerability is assigned to T1499 by the MITRE ATT&CK project.

Upgrading to version 2.7.0 eliminates this vulnerability.

The vulnerability is also documented in the vulnerability database at CERT Bund (WID-SEC-2026-3713). If you want to get best quality of vulnerability data, you may have to visit VulDB.

Affected

• Open Source Bouncy Castle

Productinfo

Vendor

• Legion of the Bouncy Castle

Name

• bc-csharp

Version

• 2.0
• 2.1
• 2.2
• 2.3
• 2.4
• 2.5
• 2.6

CPE 2.3info

• 🔒
• 🔒
• 🔒

CPE 2.2info

• 🔒
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Exploitinginfo

Threat Intelligenceinfo

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Sourcesinfo

Entryinfo

If you want to get best quality of vulnerability data, you may have to visit VulDB.

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