The vulnerability (CVE-2026-63578) exists in the PbeUtilities.GenerateCipherParameters function of Legion of the Bouncy Castle Inc. bc-csharp library versions prior to 2.7.0. It allows an attacker who can supply an encrypted private key (e.g., PKCS#8 EncryptedPrivateKeyInfo or PEM files labeled "ENCRYPTED PRIVATE KEY") to trigger excessive CPU usage by specifying an iteration count near 2^31. This count is extracted from unauthenticated algorithm parameters without an upper limit, causing the key derivation function to consume excessive resources before any password or data validation occurs. The vulnerability affects multiple password-based encryption algorithms including PKCS#5 PBES1, PBES2 (PBKDF2), PKCS#12 PBE algorithms, and CMS password recipients (CmsPbeKey). Related issues include CVE-2026-63572 and CVE-2026-63575, which cover PKCS#12 file loading and zero or negative iteration counts respectively.

An attacker capable of supplying a crafted encrypted private key can cause a denial of service by exhausting CPU resources during the key derivation process. This can disrupt services or applications relying on the affected library for password-based private-key decryption. There is no indication of direct data compromise or privilege escalation from this vulnerability alone.

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until an official fix is available, avoid processing untrusted encrypted private keys or implement application-level limits on iteration counts used in password-based key derivation. Monitor vendor channels for updates regarding a patch or official mitigation.