CVE-2017-9732 in knc
Summary
by MITRE
The read_packet function in knc (Kerberised NetCat) before 1.11-1 is vulnerable to denial of service (memory exhaustion) that can be exploited remotely without authentication, possibly affecting another services running on the targeted host.
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Analysis
by VulDB Data Team • 06/20/2023
The vulnerability identified as CVE-2017-9732 affects the knc (Kerberised NetCat) utility version 1.10 and earlier, presenting a critical denial of service condition that can be remotely exploited without authentication. This flaw exists within the read_packet function, which processes incoming network packets for Kerberos-authenticated connections. The vulnerability stems from insufficient input validation and memory management within the packet processing routine, creating a scenario where maliciously crafted network traffic can trigger excessive memory allocation patterns. The issue represents a classic memory exhaustion attack vector that can be leveraged by remote attackers to disrupt service availability. According to CWE-400, this vulnerability maps directly to the weakness category of Uncontrolled Resource Consumption, specifically manifesting as memory exhaustion. The attack surface extends beyond just the knc service itself, as the memory exhaustion can potentially impact other services running on the same host system, creating cascading availability issues. The vulnerability is particularly concerning because it operates at the network protocol level where authentication is not required for exploitation, making it accessible to any remote attacker with network connectivity to the target system.
The technical implementation of this vulnerability involves the read_packet function failing to properly validate packet sizes and content before allocating memory buffers for processing. When malformed or specially crafted packets are received, the function may allocate increasingly larger memory segments without proper bounds checking, leading to rapid memory consumption. This memory exhaustion occurs during the packet parsing phase where the utility attempts to handle Kerberos authentication tokens and network data. The flaw demonstrates characteristics consistent with CWE-129, which addresses improper validation of array indices and buffer overflows, though in this case the issue manifests as unchecked memory allocation rather than direct buffer overflow. The memory consumption pattern typically follows a predictable progression where each malicious packet triggers additional memory allocation, eventually exhausting available system memory. The attacker does not require any authentication credentials or prior access to the system, making this vulnerability particularly dangerous in networked environments where the service might be exposed to untrusted networks.
The operational impact of CVE-2017-9732 extends beyond simple service disruption to potentially compromise entire system availability and stability. When exploited, the vulnerability can cause the knc service to crash or become unresponsive, requiring manual intervention to restore functionality. The memory exhaustion can also affect other running processes on the same host, as system resources become depleted and the operating system may begin killing processes to maintain system stability. In environments where knc is used for critical network authentication services, this vulnerability could create significant operational challenges and potential security implications. The attack can be executed from any location with network access to the target system, making it particularly difficult to defend against in perimeter-based security models. According to ATT&CK framework, this vulnerability maps to T1499.004 which covers "Endpoint Denial of Service" and represents a form of resource exhaustion attack that targets system availability. The impact is particularly severe in cloud environments or containerized systems where resource limits are tight and memory exhaustion can lead to complete service outages. The vulnerability also creates potential for indirect impacts on network infrastructure, as the service disruption may affect other network-dependent systems and applications.
Mitigation strategies for CVE-2017-9732 should focus on immediate patching of the knc utility to version 1.11-1 or later, which contains the necessary memory validation and bounds checking fixes. System administrators should implement network-level restrictions to limit access to knc services, particularly when these services are exposed to untrusted networks or the internet. Network segmentation and firewall rules can help reduce the attack surface by limiting who can reach the vulnerable service. Additionally, monitoring should be implemented to detect unusual memory consumption patterns that might indicate exploitation attempts. The patch addresses the core memory management issue by implementing proper input validation and ensuring that memory allocation is bounded by reasonable limits. Organizations should also consider implementing intrusion detection systems that can identify and alert on suspicious packet patterns that match the exploit criteria. Regular security assessments should include verification that vulnerable versions are not running in production environments, and automated patch management systems should be configured to address this vulnerability promptly. The fix aligns with security best practices outlined in NIST SP 800-53 and ISO 27001 controls for vulnerability management and system security hardening.