CVE-2026-63574 Legion of the Bouncy Castle Inc. CVE debrief

Who should care

Defenders responsible for systems and applications using bc-csharp should assess exposure and prioritize patching or upgrading to version 2.7.0 or later to prevent potential denial-of-service attacks.

Why it matters

CVE-2026-63574 is a denial of service vulnerability in bc-csharp before version 2.7.0. Defenders should prioritize patching or upgrading to prevent potential attacks. The vulnerability allows remote attackers to cause a denial of service via crafted OpenPGP public keys, certificates, or signatures.

• Denial of service via OutOfMemoryException or memory exhaustion
• Potential for system crashes or instability
• Need for patching or upgrading to version 2.7.0 or later
• Verification of input validation and memory usage monitoring

Technical summary

The vulnerability exists in the SignatureSubpacketsParser.ReadPacket and UserAttributeSubpacketsParser.ReadPacket methods of bc-csharp before version 2.7.0. When parsing OpenPGP public keys, certificates, or signatures with crafted subpacket headers using the five-octet length form, an attacker can cause a denial of service due to excessive memory allocation. The lack of upper bound checking when allocating memory for subpackets in these methods can lead to an OutOfMemoryException or memory exhaustion. Defenders should prioritize patching or upgrading to version 2.7.0 or later to prevent potential denial-of-service attacks.

Defensive priority

Defenders should prioritize patching or upgrading to version 2.7.0 or later to prevent potential denial-of-service attacks.

Recommended defensive actions

• Patch or upgrade bc-csharp to version 2.7.0 or later
• Review and validate input OpenPGP public keys, certificates, and signatures
• Implement memory usage monitoring and limits for parsing processes
• Verify system configurations and validate input
• Monitor for unusual memory usage patterns
• Review compensating controls for exposed systems
• Track exceptions and retest remediated assets

Evidence notes

The vulnerability is caused by the lack of upper bound checking when allocating memory for subpackets in the SignatureSubpacketsParser.ReadPacket and UserAttributeSubpacketsParser.ReadPacket methods. This can lead to an OutOfMemoryException or memory exhaustion when parsing a crafted OpenPGP public key, certificate, or signature.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.