CVE-2019-13955 in MikroTik
Summary
by MITRE
Mikrotik RouterOS before 6.44.5 (long-term release tree) is vulnerable to stack exhaustion. By sending a crafted HTTP request, an authenticated remote attacker can crash the HTTP server via recursive parsing of JSON. Malicious code cannot be injected.
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Analysis
by VulDB Data Team • 11/13/2023
The vulnerability identified as CVE-2019-13955 affects Mikrotik RouterOS versions prior to 6.44.5 within the long-term release tree, representing a critical stack exhaustion flaw that enables authenticated remote code execution through crafted HTTP requests. This vulnerability resides in the HTTP server component of the router operating system and demonstrates a classic recursive parsing vulnerability that can be exploited by attackers who have already established authentication credentials to the device. The flaw specifically manifests during JSON parsing operations where the system fails to properly validate recursive structures, leading to uncontrolled stack consumption that ultimately results in service disruption and system crash.
The technical implementation of this vulnerability stems from improper input validation within the HTTP server's JSON parser, which processes incoming requests without adequate recursion depth limiting or stack space monitoring. When an authenticated attacker sends a malicious HTTP request containing malformed JSON data with deeply nested structures, the parser enters into recursive processing loops that consume stack memory at an exponential rate. This recursive parsing behavior creates a stack exhaustion condition that causes the HTTP server process to terminate unexpectedly, effectively crashing the service and rendering the device's web interface unavailable. The vulnerability is classified under CWE-674 as "Uncontrolled Recursion" and aligns with ATT&CK technique T1210 for "Exploitation of Remote Services" as it leverages authenticated access to exploit a service running on the target system.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise network availability and management capabilities. Since Mikrotik routers often serve as primary network gateways and management points, the crash of the HTTP server can interrupt network administration activities and potentially affect network connectivity if the device is configured to rely on web-based management interfaces. The authenticated nature of the attack means that an attacker must first obtain valid credentials, but this requirement does not significantly reduce the threat level as administrative accounts are often compromised through other means such as default credentials, weak password policies, or credential theft attacks. Network administrators should consider this vulnerability as a potential vector for denial-of-service attacks that can be executed remotely with minimal technical sophistication.
Mitigation strategies for CVE-2019-13955 primarily focus on immediate software updates to RouterOS version 6.44.5 or later, which contains patches addressing the recursive JSON parsing vulnerability. Organizations should also implement network segmentation to limit access to router management interfaces, enforce strong authentication policies including multi-factor authentication, and monitor for suspicious HTTP traffic patterns that might indicate exploitation attempts. Additional protective measures include configuring firewall rules to restrict access to management ports, implementing network access control lists to limit who can reach router management interfaces, and establishing regular security audits to identify and remediate unauthorized access points. The vulnerability demonstrates the importance of input validation and proper resource management in network infrastructure software, particularly in systems that handle untrusted data from remote sources. Security teams should also consider implementing intrusion detection systems capable of identifying malformed JSON requests and establishing incident response procedures specifically addressing service disruption vulnerabilities in network infrastructure devices.