CVE-2017-5637 in Siebel Core
Summary
by MITRE
Two four letter word commands "wchp/wchc" are CPU intensive and could cause spike of CPU utilization on Apache ZooKeeper server if abused, which leads to the server unable to serve legitimate client requests. Apache ZooKeeper thru version 3.4.9 and 3.5.2 suffer from this issue, fixed in 3.4.10, 3.5.3, and later.
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Analysis
by VulDB Data Team • 01/11/2026
The vulnerability identified as CVE-2017-5637 represents a significant denial of service weakness in Apache ZooKeeper server implementations. This issue stems from two specific four-letter command sequences: "wchp" and "wchc" that exhibit highly CPU-intensive behavior when processed by the server. These commands were designed for internal operational purposes but became exploitable by malicious actors seeking to disrupt service availability. The vulnerability affects Apache ZooKeeper versions through 3.4.9 and 3.5.2, making it a widespread concern across numerous production environments that relied on these server versions for distributed coordination services.
The technical flaw manifests through the excessive computational resources required to process these particular commands. When an attacker submits these commands to a vulnerable ZooKeeper server, the system experiences dramatic spikes in CPU utilization that can reach near 100% usage levels. This computational overhead occurs because the commands trigger internal processing loops or recursive operations that consume substantial processing cycles without proper resource limiting or rate throttling mechanisms. The commands themselves are not inherently malicious but rather represent legitimate server operations that have been misused for resource exhaustion attacks. The vulnerability falls under CWE-400, specifically addressing Uncontrolled Resource Consumption, which is a fundamental weakness in system design that allows attackers to exhaust computational resources through malformed or abusive inputs.
The operational impact of this vulnerability extends beyond simple performance degradation to complete service unavailability. When the CPU utilization spikes due to these commands, legitimate client requests cannot be processed effectively, leading to timeouts and service disruptions that can cascade throughout distributed applications relying on ZooKeeper for coordination. This creates a particularly dangerous scenario in production environments where ZooKeeper serves as a critical component for maintaining consistency and coordination across distributed systems. The attack vector is relatively simple to execute, requiring only basic network access to the ZooKeeper server and the ability to send these specific command sequences. Organizations running affected versions face potential business disruption, increased operational overhead, and potential security implications if attackers exploit this weakness to gain unauthorized access to system resources or disrupt critical services.
Mitigation strategies for CVE-2017-5637 focus primarily on upgrading to patched versions of Apache ZooKeeper, specifically versions 3.4.10, 3.5.3, and later releases that contain the necessary fixes. Organizations should prioritize immediate deployment of these updates across all affected systems to eliminate the vulnerability. Additional defensive measures include implementing network-level access controls to restrict which systems can communicate with ZooKeeper servers, configuring rate limiting mechanisms to prevent excessive command processing, and establishing monitoring systems to detect unusual CPU utilization patterns. The fix implemented in the patched versions typically involves adding proper resource limits and input validation to prevent the problematic command sequences from consuming excessive computational resources. From an ATT&CK framework perspective, this vulnerability maps to T1499.004, which covers Network Denial of Service, and represents a clear example of how seemingly benign operational commands can be weaponized to create service disruption attacks that impact availability and system integrity.