CVE-2026-59650 in Bouncy Castle
Summary
by MITRE • 08/03/2026
In Bouncy Castle for Java before 1.85, MTI/A0 DH agreement exponentiates unvalidated peer value. This issue also affects Bouncy Castle for Java LTS before 2.73.12.
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Analysis
by VulDB Data Team • 08/03/2026
The vulnerability in Bouncy Castle for Java versions prior to 1.85 and LTS versions before 2.73.12 represents a critical cryptographic flaw that undermines the security of Diffie-Hellman key agreement operations. This issue specifically affects the MTI/A0 Diffie-Hellman agreement implementation where the system fails to properly validate peer values before performing cryptographic operations. The vulnerability stems from insufficient input validation mechanisms that allow malicious actors to provide specially crafted peer values that can be exploited during the exponentiation process.
The technical flaw manifests in the MTI/A0 Diffie-Hellman agreement algorithm where unvalidated peer values are directly used in mathematical computations without proper sanitization or verification. This creates a path for attackers to potentially manipulate the cryptographic operations through carefully constructed inputs that may lead to information disclosure, key compromise, or other cryptographic vulnerabilities. The weakness lies in the failure to implement proper bounds checking and validation of peer public values before these values are processed within the Diffie-Hellman exponentiation calculations.
From an operational perspective, this vulnerability poses significant risks to systems relying on Bouncy Castle for Java cryptographic operations, particularly those implementing MTI/A0 key agreement protocols. An attacker could potentially exploit this weakness to recover private keys, decrypt communications, or perform man-in-the-middle attacks against TLS connections and other security protocols that depend on secure Diffie-Hellman key exchange mechanisms. The impact extends beyond simple data confidentiality as it can compromise the entire cryptographic infrastructure built upon these vulnerable components.
The vulnerability aligns with CWE-20, which addresses "Improper Input Validation" in cryptographic contexts, and represents a classic example of insufficient validation of cryptographic parameters that can lead to serious security implications. Organizations using affected Bouncy Castle versions should immediately upgrade to patched releases to mitigate the risk of exploitation. The recommended mitigation strategy includes implementing proper input validation for all peer values used in Diffie-Hellman operations and ensuring that cryptographic libraries are regularly updated to address known vulnerabilities. Additionally, system administrators should conduct comprehensive vulnerability assessments to identify any applications still utilizing affected Bouncy Castle versions and ensure proper security controls are implemented across the infrastructure.