Quick answers
- Is CVE-2026-103603 exploited in the wild?
- No. Junglewise Threat Intelligence has no report of CVE-2026-103603 being exploited in the wild.
- How severe is CVE-2026-103603?
- Informational severity, published 2 October 2026.
- Which products and versions are affected?
- Legion of the Bouncy Castle Inc. BouncyCastle.Cryptography before 2.7.0.
- Is there a fix for CVE-2026-103603?
- Yes: fixed in BouncyCastle.Cryptography 2.7.0. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
- How is CVE-2026-103603 attacked?
- It is attacked over the network, in a software library.
- Am I affected by CVE-2026-103603?
- Check whether you run Legion of the Bouncy Castle Inc. BouncyCastle.Cryptography 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.
How to fix
- Fixed in: BouncyCastle.Cryptography 2.7.0
Technical details
The HSS/LMS public key parser in HssPublicKeyParameters fails to validate that the level count (L) parameter complies with RFC 8554's maximum of 8, allowing an attacker-supplied value to exceed this limit. During signature verification, the code allocates an array of L-1 entries before validating further data, enabling memory exhaustion. A single verification can consume approximately 17 GB or trigger an OutOfMemoryException.
Affected products
- Legion of the Bouncy Castle Inc. BouncyCastle.Cryptography before 2.7.0
Timeline
- 2026-10-02: disclosed
- 2026-06-15: patched: Fix committed adding RFC 8554 validation for L parameter range (1-8)