# CVE-2026-59642: Bouncy Castle CMS AuthenticatedData MAC bypass with authAttrs

Source: https://junglewise.ai/threats/cve-2026-59642-bouncy-castle-cms-authenticateddata-mac-bypass-with-authattrs  
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-2026-59642 · Severity: high · CVSS 7.5 · Published 2026-08-03

Bouncy Castle is a widely-used cryptographic library for Java that handles digital signatures and encrypted communications. In affected versions, CMS (Cryptographic Message Syntax) authenticated messages with certain attributes can bypass MAC (message authentication code) verification, allowing an attacker to forge or tamper with authenticated messages without detection.

Technologies: [Bouncy Castle for Java](https://junglewise.ai/threats/technologies/bouncy-castle-for-java), [Bouncy Castle for Java FIPS](https://junglewise.ai/threats/technologies/bouncy-castle-for-java-fips), [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-2026-59642 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-59642 being exploited in the wild.

**How severe is CVE-2026-59642?** High severity, with a CVSS score of 7.5, published 3 August 2026.

**Which products and versions are affected?** Bouncy Castle for Java before 1.85; Bouncy Castle for Java FIPS bcpkix-fips before 1.0.12 (1.0.X), before 2.0.12 (2.0.X), before 2.1.12 (2.1.X).

**Is there a fix for CVE-2026-59642?** 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-2026-59642 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-59642?** Check whether you run Bouncy Castle for Java, Bouncy Castle for Java FIPS 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

This vulnerability is a cryptographic bypass in CMS AuthenticatedData processing. When authenticated attributes (authAttrs) are present, the content is not properly bound to the MAC calculation, allowing an attacker to forge or modify the authenticated data. The vulnerability affects Bouncy Castle for Java versions before 1.85, Java LTS before 2.73.12, and FIPS variants (BC-FJA) in multiple series (before 1.0.12 for 1.0.X, before 2.0.12 for 2.0.X, and before 2.1.12 for 2.1.X). Attack requires network access to systems using the vulnerable library for CMS message processing, and no authentication is required. An attacker can forge cryptographically authenticated messages or tamper with existing ones. Patches are available in the versions listed above.

## Affected products

- Bouncy Castle Bouncy Castle for Java before 1.85
- Bouncy Castle Bouncy Castle for Java LTS before 2.73.12
- Bouncy Castle Bouncy Castle for Java FIPS bcpkix-fips before 1.0.12 (1.0.X), before 2.0.12 (2.0.X), before 2.1.12 (2.1.X)

## 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/)

## Related threats

- [Bouncy Castle for Java truncated OpenPGP message acceptance](https://junglewise.ai/threats/cve-2026-85515-in-bouncy-castle-for-java-before-1-86-a-truncated-openpgp)
- [Bouncy Castle for Java BLS signature phantom signer](https://junglewise.ai/threats/cve-2026-71891-in-bouncy-castle-for-java-before-1-86-bls12-381basicscheme)
- [Bouncy Castle MLS external commit validation bypass](https://junglewise.ai/threats/cve-2026-71890-in-bouncy-castle-for-java-before-1-86-validation-of-an-mls-rfc)
- [Bouncy Castle for Java X.509 name constraints bypass in PKIXCertPathReviewer](https://junglewise.ai/threats/cve-2026-71889-in-bouncy-castle-for-java-before-1-86-neither-copy-of)
- [Bouncy Castle for Java OpenPGP signature misattribution in subkey binding validation](https://junglewise.ai/threats/cve-2026-71887-in-bouncy-castle-for-java-before-1-86-the-high-level-openpgp-api)