CVE-2021-20264 in OpenJDK
Summary
by MITRE • 10/06/2021
An insecure modification flaw in the /etc/passwd file was found in the openjdk-1.8 and openjdk-11 containers. This flaw allows an attacker with access to the container to modify the /etc/passwd and escalate their privileges. The highest threat from this vulnerability is to confidentiality, integrity, as well as system availability.
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Analysis
by VulDB Data Team • 10/10/2021
The vulnerability identified as CVE-2021-20264 represents a critical security flaw within OpenJDK container images that affects both version 1.8 and 11 distributions. This issue stems from improper file permissions and access controls surrounding the /etc/passwd file within the containerized environment, creating a pathway for privilege escalation attacks. The flaw specifically targets the container's file system security model where unauthorized modifications to the passwd file can occur, fundamentally compromising the system's authentication and authorization mechanisms.
The technical implementation of this vulnerability resides in the container's file system permissions and the way the OpenJDK images handle user account management. When an attacker gains access to the container environment, they can manipulate the /etc/passwd file to modify user account information, potentially creating new user accounts with elevated privileges or altering existing account permissions. This insecure modification capability directly violates the principle of least privilege and allows for unauthorized access to system resources that should remain protected. The flaw operates at the operating system level within the container, leveraging the underlying host system's file permissions and the container's security context.
The operational impact of CVE-2021-20264 extends beyond simple privilege escalation, affecting all three core principles of information security. Confidentiality is compromised as attackers can gain access to user accounts and potentially sensitive data that these accounts control. Integrity suffers because unauthorized modifications to the passwd file can alter user authentication data, creating backdoors or disabling legitimate user accounts. System availability is also at risk as attackers can manipulate account permissions to lock out legitimate users or create excessive resource consumption through privilege escalation. This vulnerability aligns with CWE-276, which addresses incorrect permissions for critical resources, and represents a direct violation of the principle of least privilege in container security.
Organizations utilizing OpenJDK containers must implement immediate mitigation strategies to address this vulnerability. The primary approach involves updating to patched versions of the OpenJDK containers that properly secure the /etc/passwd file permissions and implement proper access controls. Container runtime configurations should be reviewed to ensure that file system mounts and permissions are properly restricted, preventing unauthorized access to critical system files. Security teams should implement monitoring for unauthorized modifications to system files and establish regular vulnerability scanning procedures for container images. Additionally, container images should be built with minimal necessary privileges and proper security hardening measures. This vulnerability demonstrates the critical importance of container security and aligns with ATT&CK technique T1068, which covers 'Exploitation for Privilege Escalation', making it essential for security operations to address container-level privilege escalation risks.
The broader implications of this vulnerability highlight the increasing complexity of securing containerized environments and the need for comprehensive security strategies that address both application-level and infrastructure-level threats. Organizations must recognize that container security is not merely about securing the application itself but also about protecting the underlying container environment from privilege escalation attacks. This flaw underscores the necessity of implementing proper security controls at every layer of the container stack and demonstrates why continuous security monitoring and regular patch management are critical for maintaining secure container deployments.