CVE-2015-8539 in Linux
Summary
by MITRE
The KEYS subsystem in the Linux kernel before 4.4 allows local users to gain privileges or cause a denial of service (BUG) via crafted keyctl commands that negatively instantiate a key, related to security/keys/encrypted-keys/encrypted.c, security/keys/trusted.c, and security/keys/user_defined.c.
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Analysis
by VulDB Data Team • 07/07/2022
The vulnerability identified as CVE-2015-8539 resides within the Linux kernel's KEYS subsystem, specifically affecting versions prior to 4.4. This flaw represents a critical security weakness that enables local attackers to escalate privileges or execute denial of service attacks through carefully crafted keyctl commands. The vulnerability manifests in the kernel's handling of key instantiation processes, particularly within the encrypted-keys, trusted keys, and user-defined keys components. The security implications are significant as the KEYS subsystem forms a fundamental part of the kernel's security architecture, managing cryptographic keys and access controls for various security mechanisms.
The technical exploitation of this vulnerability occurs when malicious users submit crafted keyctl commands that attempt to negatively instantiate keys within the kernel's key management system. This process involves manipulating the key creation and validation logic in the affected source files including encrypted.c, trusted.c, and user_defined.c. The flaw stems from insufficient validation of key parameters and instantiation states, allowing attackers to trigger unexpected kernel behavior that can result in privilege escalation or system instability. The vulnerability operates at the kernel level, making it particularly dangerous as it can be exploited by any local user with access to the system, regardless of their initial privilege level.
From an operational perspective, this vulnerability creates substantial risk for Linux systems as it allows local privilege escalation without requiring special privileges or external network access. The impact extends beyond simple privilege elevation to include potential denial of service conditions that can cause system crashes or instability. Attackers can leverage this vulnerability to gain root access or render systems unusable through carefully constructed keyctl operations. The attack vector is particularly concerning because it requires minimal prerequisites and can be executed from any local session, making it a preferred target for both malicious actors and security researchers. The vulnerability's presence in core kernel subsystems means that affected systems may experience complete compromise or service disruption.
Mitigation strategies for CVE-2015-8539 primarily involve upgrading to Linux kernel version 4.4 or later, which contains the necessary patches to address the key instantiation validation issues. System administrators should prioritize applying kernel updates and ensuring all systems are running patched versions. Additional protective measures include implementing strict access controls for keyctl commands, monitoring for suspicious key management activities, and maintaining up-to-date security configurations. The vulnerability aligns with CWE-119, which addresses "Improper Access to Memory" and specifically relates to memory safety issues in kernel space operations. From an attack framework perspective, this vulnerability could be classified under ATT&CK technique T1068, which covers "Exploitation for Privilege Escalation," demonstrating how local users can leverage kernel flaws to gain elevated system privileges. Organizations should also consider implementing kernel hardening measures and monitoring for anomalous key management behavior as part of their overall security posture.