CVE-2010-0500 in Mac OS X
Summary
by MITRE
Event Monitor in Apple Mac OS X before 10.6.3 does not properly validate hostnames of SSH clients, which allows remote attackers to cause a denial of service (arbitrary client blacklisting) via a crafted DNS PTR record, related to a "plist injection issue."
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Analysis
by VulDB Data Team • 05/04/2026
The vulnerability described in CVE-2010-0500 resides within Apple Mac OS X Event Monitor functionality prior to version 10.6.3, specifically targeting the SSH client hostname validation process. This issue represents a classic case of insufficient input validation that enables malicious actors to manipulate system behavior through carefully crafted network responses. The flaw occurs during the hostname resolution process when the system attempts to validate SSH client connections by performing DNS lookups to determine hostnames. The Event Monitor component fails to properly sanitize or validate the hostname data returned from these DNS queries, creating a pathway for exploitation that can be leveraged to disrupt normal system operations.
The technical implementation of this vulnerability stems from a plist injection issue that manifests when the system processes DNS PTR records for SSH client identification. When an attacker controls or can influence DNS responses for a target host, they can craft malicious PTR records that contain specially formatted data structures designed to exploit the Event Monitor's parsing logic. This injection occurs because the system does not adequately validate the structure and content of hostname data retrieved from DNS queries, allowing malformed or maliciously constructed data to be interpreted as legitimate hostname information. The vulnerability specifically targets the handling of reverse DNS lookups where PTR records are used to resolve IP addresses back to hostnames, creating a vector through which attackers can manipulate the system's client identification process.
The operational impact of this vulnerability extends beyond simple denial of service to include potential arbitrary client blacklisting capabilities that can disrupt legitimate SSH connections and compromise system availability. Attackers can leverage this flaw to systematically block access to SSH services by injecting malicious hostname data that causes the Event Monitor to incorrectly classify legitimate clients as unauthorized or suspicious. This blacklisting mechanism can be used to create persistent denial of service conditions where legitimate users cannot establish SSH connections to affected systems. The vulnerability also represents a significant security risk as it can be exploited to bypass certain access controls or create false positives that could be used in more sophisticated attack scenarios. The issue demonstrates how seemingly minor input validation flaws can have cascading effects on system security and availability.
Mitigation strategies for CVE-2010-0500 should focus on both immediate system updates and operational security improvements. The primary and most effective solution involves applying the official Apple security update that addresses this specific validation issue in Mac OS X 10.6.3 and later versions. Organizations should also implement DNS security measures including DNSSEC validation to prevent unauthorized modifications to DNS records that could be used to exploit this vulnerability. Network segmentation and monitoring of DNS traffic can help detect unusual PTR record activity that might indicate exploitation attempts. Additionally, implementing proper access control lists and connection tracking mechanisms can provide alternative protection against unauthorized client blacklisting. From a compliance perspective, this vulnerability aligns with CWE-20 Input Validation and CWE-119 Improper Restriction of Operations within a Memory Buffer categories, and maps to ATT&CK technique T1071.004 Application Layer Protocol: DNS, highlighting the importance of network protocol security in preventing such exploitation vectors.