CVE-2017-9671 in apk
Summary
by MITRE
A heap overflow in apk (Alpine Linux's package manager) allows a remote attacker to cause a denial of service, or achieve code execution, by crafting a malicious APKINDEX.tar.gz file with a bad pax header block.
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Analysis
by VulDB Data Team • 11/09/2019
The heap overflow vulnerability in apk represents a critical security flaw within Alpine Linux's package management system that exposes systems to remote code execution and denial of service attacks. This vulnerability specifically targets the parsing mechanism of APKINDEX.tar.gz files, which are used by the apk package manager to maintain package repositories and metadata. The flaw manifests when the system processes maliciously crafted archive files containing malformed pax header blocks that exceed allocated heap memory boundaries. The vulnerability resides in the improper handling of archive metadata during package index parsing operations, where the apk utility fails to properly validate or constrain the size of header data structures before allocating memory for their processing. This issue affects the core functionality of Alpine Linux package management and can be exploited by attackers who gain the ability to upload or modify package repositories, potentially compromising entire systems that rely on the apk package manager for software distribution and updates.
The technical implementation of this heap overflow stems from inadequate bounds checking within the pax header processing code path. When the apk utility encounters a malicious APKINDEX.tar.gz file, it attempts to parse the pax extended header entries without sufficient validation of the header block sizes. The pax format specification allows for variable-length extended attributes, but the apk implementation does not properly enforce maximum size limits or validate the integrity of these header structures. This lack of input sanitization creates a condition where attacker-controlled data can cause heap memory allocation to exceed expected boundaries, leading to memory corruption that can be leveraged for arbitrary code execution. The vulnerability follows the common pattern of heap-based buffer overflows where insufficient bounds checking allows attackers to overwrite adjacent memory regions, potentially corrupting program state or executing malicious code. This flaw directly relates to CWE-121, heap-based buffer overflow, and demonstrates poor input validation practices in archive processing components. The attack vector requires remote access to package repositories, making it particularly dangerous for systems that automatically update from internet-based package sources.
The operational impact of this vulnerability extends beyond simple denial of service to encompass full system compromise potential. An attacker who can manipulate package repositories can craft malicious APKINDEX.tar.gz files that trigger the heap overflow when legitimate systems attempt to update their package databases. This creates a persistent threat vector where systems automatically download and process malicious package metadata, potentially leading to remote code execution on target systems. The vulnerability affects all versions of apk prior to the security patch, making it particularly dangerous for systems using older Alpine Linux releases or custom package repositories. The exploitability of this vulnerability is enhanced by the fact that package managers typically run with elevated privileges during update operations, providing attackers with potential privilege escalation opportunities. Additionally, the vulnerability can be chained with other exploits to create more sophisticated attack scenarios, as demonstrated by various ATT&CK techniques involving privilege escalation and persistence mechanisms. Organizations using Alpine Linux containers, embedded systems, or any infrastructure relying on apk package management are at risk of being compromised through this vulnerability.
Mitigation strategies for CVE-2017-9671 require immediate patching of the apk package manager to address the heap overflow vulnerability. System administrators should upgrade to patched versions of Alpine Linux that contain the necessary memory validation fixes for pax header processing. Organizations should implement repository validation mechanisms that verify package metadata integrity before processing, including checksum verification of APKINDEX.tar.gz files and digital signature validation. Network segmentation and access controls should be implemented to limit which systems can modify or access package repositories, reducing the attack surface for this vulnerability. Regular monitoring of package repository contents and implementation of automated scanning tools can help detect malicious package metadata before it affects system updates. Security teams should also consider implementing runtime protections such as address space layout randomization and stack canaries to make exploitation more difficult. The vulnerability highlights the importance of proper input validation in archive processing components and demonstrates the necessity of comprehensive security testing for package management systems. Organizations should conduct regular security assessments of their package management infrastructure and maintain up-to-date security patches for all system components to prevent similar vulnerabilities from being exploited in the future.