CVE-2017-5495 in Quagga
Summary
by MITRE
All versions of Quagga, 0.93 through 1.1.0, are vulnerable to an unbounded memory allocation in the telnet 'vty' CLI, leading to a Denial-of-Service of Quagga daemons, or even the entire host. When Quagga daemons are configured with their telnet CLI enabled, anyone who can connect to the TCP ports can trigger this vulnerability, prior to authentication. Most distributions restrict the Quagga telnet interface to local access only by default. The Quagga telnet interface 'vty' input buffer grows automatically, without bound, so long as a newline is not entered. This allows an attacker to cause the Quagga daemon to allocate unbounded memory by sending very long strings without a newline. Eventually the daemon is terminated by the system, or the system itself runs out of memory. This is fixed in Quagga 1.1.1 and Free Range Routing (FRR) Protocol Suite 2017-01-10.
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Analysis
by VulDB Data Team • 05/14/2026
The vulnerability identified as CVE-2017-5495 affects Quagga routing software versions 0.93 through 1.1.0, presenting a critical denial-of-service risk through unbounded memory allocation in the telnet virtual terminal interface. This flaw exists within the vty (virtual terminal) subsystem that handles command-line interface connections via telnet protocol, making it particularly dangerous as it can be exploited before authentication occurs. The vulnerability stems from the improper handling of input buffer management where the vty subsystem automatically expands its input buffer without any upper limits, creating a condition where memory allocation continues indefinitely until system resources are exhausted.
The technical implementation of this vulnerability resides in the lack of input validation and buffer size constraints within the telnet CLI processing logic. When Quagga daemon services are configured to accept telnet connections, any remote attacker with network access to the configured TCP ports can exploit this flaw by sending continuous streams of data without terminating characters. The vty subsystem continues to allocate memory for the input buffer as long as no newline character is received, allowing an attacker to consume system memory at an uncontrolled rate. This behavior represents a classic buffer overflow condition that has been reclassified as an unbounded memory allocation issue, where the absence of bounds checking creates a resource exhaustion scenario rather than a traditional stack or heap overflow.
The operational impact of CVE-2017-5495 extends beyond simple service disruption to potentially compromise entire host systems through memory exhaustion attacks. When exploited successfully, the vulnerability causes Quagga daemon processes to consume all available memory resources, leading to system instability, process termination by the operating system's out-of-memory killer, or complete system hang. This makes the vulnerability particularly dangerous in network infrastructure environments where routing daemons are critical for network operations, as it can effectively disable network connectivity and routing functions. The vulnerability affects not only individual daemon processes but can potentially cause cascading failures across network infrastructure components that depend on stable routing services.
Mitigation strategies for CVE-2017-5495 involve immediate patching to Quagga version 1.1.1 or migration to the Free Range Routing (FRR) Protocol Suite 2017-01-10, which contains the necessary fixes for input buffer management. Network administrators should also implement network segmentation and access controls to restrict telnet access to Quagga services, ensuring that only authorized personnel can connect to these interfaces. Additionally, monitoring systems should be configured to detect unusual memory consumption patterns in routing daemon processes, and network access control lists should be implemented to limit access to telnet ports to trusted networks only. The fix addresses the root cause by implementing proper input buffer size limits and ensuring that the vty subsystem enforces reasonable memory allocation boundaries, preventing the unbounded growth of input buffers that led to the vulnerability. This remediation aligns with cybersecurity best practices for input validation and resource management, and corresponds to mitigations recommended under the ATT&CK framework for network service exploitation techniques and privilege escalation through resource exhaustion attacks.