# CVE-2026-59648: Bouncy Castle OpenPGP Argon2 S2K weak parameter validation

Source: https://junglewise.ai/threats/cve-2026-59648-bouncy-castle-openpgp-argon2-s2k-weak-parameter-validation  
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-2026-59648 · Severity: medium · CVSS 5.3 · Published 2026-08-03

Bouncy Castle is a widely-used cryptographic library for Java applications. A flaw in OpenPGP key derivation (Argon2 S2K) allows attackers to force the use of weak memory and iteration parameters, potentially making encrypted keys easier to crack through brute-force attacks. This could compromise the security of PGP-encrypted data and private keys stored using affected versions.

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

## Quick answers

**Is CVE-2026-59648 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-59648 being exploited in the wild.

**How severe is CVE-2026-59648?** Medium severity, with a CVSS score of 5.3, published 3 August 2026.

**Which products and versions are affected?** Bouncycastle Bouncy Castle for Java FIPS (bcpg-fips) before 1.0.13 (1.0.X), 2.0.13 (2.0.X), 2.1.13 (2.1.X); Bouncycastle Bouncy Castle For Java Lts before 2.73.12.

**Is there a fix for CVE-2026-59648?** 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-2026-59648 attacked?** It is attacked over the network or with local access.

**Am I affected by CVE-2026-59648?** Check whether you run Bouncycastle Bouncy Castle for Java FIPS (bcpg-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

The vulnerability exists in the OpenPGP Argon2 S2K (string-to-key) implementation, where attacker-supplied memory and pass parameters are not properly validated or constrained. An attacker can craft malformed OpenPGP key material that specifies artificially low memory requirements or iteration counts, reducing the computational cost needed to brute-force the derived key. The attack requires network or local access to process attacker-controlled OpenPGP data. Patches are available in Bouncy Castle for Java 1.85+, LTS 2.73.12+, and BC-FJA FIPS versions 1.0.13, 2.0.13, and 2.1.13 or later.

## Affected products

- Bouncycastle Bouncy Castle for Java before 1.85
- Bouncycastle Bouncy Castle for Java LTS before 2.73.12
- Bouncycastle Bouncy Castle for Java FIPS (bcpg-fips) before 1.0.13 (1.0.X), 2.0.13 (2.0.X), 2.1.13 (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/)

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