CVE-2017-5836 in libplist
Summary
by MITRE
The plist_free_data function in plist.c in libplist allows attackers to cause a denial of service (crash) via vectors involving an integer node that is treated as a PLIST_KEY and then triggers an invalid free.
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Analysis
by VulDB Data Team • 09/04/2020
The vulnerability identified as CVE-2017-5836 resides within the libplist library, specifically in the plist_free_data function located in plist.c. This issue represents a classic case of improper input validation and memory management handling that can be exploited to trigger a denial of service condition. The flaw manifests when processing malformed plist data structures where an integer node is incorrectly interpreted as a PLIST_KEY type, leading to subsequent memory corruption during the cleanup process. The root cause stems from inadequate type checking and validation mechanisms within the library's parsing and freeing routines, creating a scenario where legitimate memory operations become invalid due to type confusion.
This vulnerability operates at the intersection of memory safety and input validation, aligning with CWE-121 which addresses stack buffer overflow conditions and CWE-476 which covers null pointer dereference issues. The attack vector involves sending specially crafted plist data to any application or service that utilizes the libplist library for parsing configuration files or data exchange. When the vulnerable library attempts to free memory associated with the malformed node, it treats integer data as if it were a key structure, resulting in an invalid free operation that typically causes a segmentation fault or crash. The operational impact extends beyond simple service disruption as this vulnerability can be leveraged in broader attack scenarios including application stability compromise and potential escalation in multi-layered attack chains.
The technical exploitation requires minimal prerequisites and can be executed through various means including file-based attacks, network-based data injection, or even embedded payload delivery within legitimate plist files. Systems utilizing libplist for processing user-supplied or third-party data are particularly vulnerable, including mobile device management systems, configuration management tools, and any software that handles plist formatted data structures. The vulnerability demonstrates a fundamental flaw in the library's memory management practices where the free function does not properly validate the node type before attempting memory deallocation, creating a direct pathway for crash generation. This issue particularly affects systems where plist data is processed without proper sanitization or validation, making it a significant concern for enterprise environments and security-critical applications.
Mitigation strategies for CVE-2017-5836 focus on immediate library updates and implementation of proper input validation controls. Organizations should prioritize upgrading to patched versions of libplist where the plist_free_data function has been corrected to properly validate node types before memory deallocation operations. Additionally, implementing defensive programming practices including input sanitization, type checking, and proper error handling can significantly reduce the attack surface. The fix typically involves adding explicit type validation checks within the plist_free_data function to ensure that nodes are properly identified as their intended types before any memory management operations are performed. Network segmentation and application whitelisting can serve as additional protective measures while patches are deployed, and monitoring for unusual crash patterns or service disruptions can help detect exploitation attempts. From an ATT&CK framework perspective, this vulnerability maps to T1499 which covers network disruption and T1566 which addresses malicious file execution, making it a critical target for both preventive and detective security controls.