# CVE-2026-59650: Bouncy Castle MTI/A0 DH agreement unvalidated peer value

Source: https://junglewise.ai/threats/cve-2026-59650-bouncy-castle-mti-a0-dh-agreement-unvalidated-peer-value  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-08-03. Updated: 2026-09-25  
License: CC BY 4.0 with a link back

CVE-2026-59650 · Severity: critical · CVSS 9.1 · Published 2026-08-03

Bouncy Castle is a widely-used cryptographic library for Java applications. This vulnerability allows an attacker to bypass security validation in Diffie-Hellman key agreement operations by providing unvalidated peer values, potentially compromising the confidentiality and integrity of encrypted communications that rely on this library for key exchange.

Technologies: [Bouncy Castle for Java](https://junglewise.ai/threats/technologies/bouncy-castle-for-java), [Bouncycastle Bouncy Castle For Java Lts](https://junglewise.ai/threats/technologies/bouncy-castle-for-java-lts). Vendors: [Bouncy Castle](https://junglewise.ai/threats/vendors/bouncy-castle), [Bouncycastle](https://junglewise.ai/threats/vendors/bouncycastle).

## Quick answers

**Is CVE-2026-59650 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-59650 being exploited in the wild.

**How severe is CVE-2026-59650?** Critical severity, with a CVSS score of 9.1, published 3 August 2026.

**Which products and versions are affected?** Bouncy Castle for Java before 1.85.

**Is there a fix for CVE-2026-59650?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-59650 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-59650?** Check whether you run Bouncy Castle for Java or Bouncycastle Bouncy Castle For Java Lts at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

The vulnerability exists in the MTI/A0 Diffie-Hellman agreement implementation in Bouncy Castle for Java, which fails to properly validate peer-supplied values before performing modular exponentiation. An attacker can exploit this by providing specially crafted DH parameters that skip validation checks, potentially allowing cryptographic weakening or key recovery attacks. The issue affects Bouncy Castle for Java versions before 1.85 and Java LTS versions before 2.73.12. The vulnerability is network-reachable in applications that perform DH key agreement with untrusted peers, with no authentication required beyond the ability to participate in the key exchange protocol. Patches are available in the specified fixed versions.

## Affected products

- Bouncy Castle Bouncy Castle for Java before 1.85
- Bouncy Castle Bouncy Castle for Java LTS before 2.73.12

## Timeline

- 2026-08-03: disclosed

## References

- [https://www.bouncycastle.org/download/bouncy-castle-java/](https://www.bouncycastle.org/download/bouncy-castle-java/)
- [https://www.bouncycastle.org/download/bouncy-castle-java-lts/](https://www.bouncycastle.org/download/bouncy-castle-java-lts/)

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