Is CVE-2026-59639 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-59639 being exploited in the wild.

How severe is CVE-2026-59639?

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 series), before 2.0.12 (2.0.X series), before 2.1.12 (2.1.X series).

Is there a fix for CVE-2026-59639?

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-2026-59639 attacked?

It is attacked over the network.

Am I affected by CVE-2026-59639?

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.

CVE-2026-59639: Bouncy Castle for Java CMS signature verification bypass

CVE-2026-59639 · Severity: high · CVSS 7.5 · Published 2026-08-03

Bouncy Castle is a widely-used cryptographic library for Java applications. This vulnerability allows the CMS signature verification function to incorrectly return success when validating a signed message with zero signers, bypassing security controls. Applications relying on Bouncy Castle to verify digital signatures may accept forged or tampired messages as legitimate, potentially compromising data integrity and authentication.

Technologies: Bouncy Castle for Java, Bouncy Castle for Java FIPS, Bouncycastle Bouncy Castle For Java Lts. Vendors: Bouncy Castle, Bouncycastle.

Quick answers

Is CVE-2026-59639 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-59639 being exploited in the wild.
How severe is CVE-2026-59639?: 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 series), before 2.0.12 (2.0.X series), before 2.1.12 (2.1.X series).
Is there a fix for CVE-2026-59639?: 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-2026-59639 attacked?: It is attacked over the network.
Am I affected by CVE-2026-59639?: 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 validation bypass in the Bouncy Castle CMS (Cryptographic Message Syntax) module. The verifySignatures method incorrectly returns true for SignedData objects containing zero signers, a condition that should fail validation. The root cause is insufficient input validation on the signer list before performing verification checks. No authentication or special network access is required; any application using the affected verifySignatures API is at risk if it processes untrusted CMS SignedData. An attacker can craft a forged SignedData message with no valid signers and have it accepted as legitimate, enabling message forgery and tampering attacks. Patches are available in Bouncy Castle for Java 1.85+, Java LTS 2.73.12+, and Bouncy Castle for Java FIPS in bcpkix-fips 1.0.12, 2.0.12, and 2.1.12.

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 series), before 2.0.12 (2.0.X series), before 2.1.12 (2.1.X series)

Timeline

2026-08-03: disclosed: Vulnerability disclosed and published on NVD

References

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