CVE-2018-19589 in CryptoServer HSM
Summary
by MITRE
Incorrect Access Controls of Security Officer (SO) in PKCS11 R2 provider that ships with the Utimaco CryptoServer HSM product package allows an SO authenticated to a slot to retrieve attributes of keys marked as private keys in external key storage, and also delete keys marked as private keys in external key storage. This compromises the availability of all keys configured with external key storage and may result in an economic attack in which the attacker denies legitimate users access to keys while maintaining possession of an encrypted copy (blob) of the external key store for ransom. This attack has been dubbed reverse ransomware attack and may be executed via a physical connection to the CryptoServer or remote connection if SSH or remote access to LAN CryptoServer has been compromised. The Confidentiality and Integrity of the affected keys, however, remain untarnished.
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Analysis
by VulDB Data Team • 05/28/2020
The vulnerability described in CVE-2018-19589 represents a critical access control flaw within the PKCS#11 R2 provider of Utimaco CryptoServer HSM products, specifically targeting the Security Officer (SO) role permissions. This issue stems from improper implementation of access controls that should normally restrict SO privileges to only authorized operations within the hardware security module environment. The flaw allows authenticated SO users to bypass normal security boundaries when interacting with external key storage components, creating a significant escalation path for attackers who have gained SO-level access to a cryptographic slot.
The technical implementation of this vulnerability manifests through the failure of the PKCS#11 provider to properly enforce attribute restrictions on private keys stored in external storage systems. When an SO authenticates to a slot, the system incorrectly grants access to private key attributes and deletion capabilities that should remain restricted to authorized key management operations. This misconfiguration creates a scenario where legitimate security controls are circumvented, allowing unauthorized operations on keys that are specifically marked as private within the external key storage framework. The vulnerability operates at the interface level between the cryptographic application and the HSM, specifically within the PKCS#11 compliance layer that governs cryptographic operations.
From an operational impact perspective, this vulnerability creates a severe availability compromise for all keys configured with external key storage mechanisms. The ability to delete private keys from external storage directly undermines the availability of cryptographic services, potentially rendering systems unable to perform decryption or signature operations using those keys. The economic implications are particularly concerning as this vulnerability enables what security researchers have termed "reverse ransomware" attacks, where attackers maintain possession of encrypted key copies while denying legitimate users access to their cryptographic keys. This creates a unique threat model where the attacker can demand ransom payments for key recovery while maintaining operational control over the cryptographic infrastructure.
The attack vectors for exploiting this vulnerability are diverse and include both physical and network-based access scenarios. Physical connection to the CryptoServer provides direct access to exploit the flaw, while remote compromise through SSH or LAN access creates additional attack surface opportunities. The vulnerability's exploitation potential aligns with ATT&CK technique T1552.001 (Unsecured Credentials) and T1499.004 (Authorization Script Injection) as attackers can leverage legitimate SO access to escalate privileges and perform unauthorized key operations. This represents a sophisticated attack pattern that combines privilege escalation with availability disruption.
Security controls for mitigating this vulnerability should focus on implementing proper access control enforcement within the PKCS#11 provider, ensuring that SO roles cannot access private key attributes or perform deletion operations on external key storage. Organizations should implement strict privilege separation between different security roles, particularly between Security Officers and key management personnel. The mitigation strategy should include regular access reviews, monitoring of SO activities, and implementation of additional layers of authentication for critical key operations. This vulnerability specifically relates to CWE-284 (Improper Access Control) and CWE-312 (Sensitive Data Exposure) categories, with the latter being particularly relevant due to the potential for attackers to gain access to key material through the unauthorized deletion operations.
The threat landscape surrounding this vulnerability demonstrates the growing sophistication of attacks targeting cryptographic infrastructure, particularly within HSM environments where the compromise of a single access point can lead to widespread cryptographic service disruption. Organizations using Utimaco CryptoServer products should immediately implement access control hardening measures, conduct comprehensive security assessments of their PKCS#11 implementations, and establish monitoring procedures to detect unauthorized key deletion activities. The vulnerability's impact extends beyond simple availability concerns to encompass potential financial losses through ransom demands and operational disruption costs, making it a critical security priority for organizations relying on cryptographic key management systems.