CVE-2002-2124 in Nylon
Summary
by MITRE
The recvn and sendn functions in nylon 0.2 do not check when the recv function call returns 0, which allows remote attackers to cause a denial of service (infinite loop and CPU consumption) by closing the connection while recv is executing.
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Analysis
by VulDB Data Team • 06/28/2021
The vulnerability identified as CVE-2002-2124 resides within the nylon 0.2 network library implementation where the recvn and sendn functions fail to properly handle the scenario when the underlying recv system call returns zero bytes. This fundamental flaw creates a critical condition that can be exploited by remote attackers to execute a denial of service attack. The issue stems from the improper handling of connection closure events during active data transfer operations, specifically when the remote peer terminates the connection while data reception is in progress.
The technical root cause of this vulnerability can be categorized under CWE-681, which addresses incorrect use of a resource in a manner that can lead to resource exhaustion or system instability. When the recv function returns zero bytes, it typically indicates that the remote peer has closed the connection gracefully. However, the nylon 0.2 implementation does not account for this condition in its recvn and sendn functions, leading to an infinite loop scenario where the application continues to call recv without proper termination conditions. This behavior consumes excessive CPU cycles and effectively renders the affected system unavailable to legitimate users.
From an operational perspective, this vulnerability presents a significant risk to network services that rely on the nylon library for communication handling. The attack vector requires only that a remote attacker establish a connection and then close it during active data transfer, making the exploit relatively simple to execute. The resulting denial of service condition can persist until the affected process is manually terminated or the system is rebooted, creating substantial availability concerns for critical infrastructure components. The infinite loop behavior specifically targets CPU utilization, potentially causing systems to become unresponsive and unable to handle legitimate connection requests.
The attack pattern aligns with ATT&CK technique T1499.004, which covers "Endpoint Denial of Service" through resource exhaustion. This vulnerability represents a classic example of how improper error handling in network protocols can be leveraged to consume system resources and disrupt service availability. The impact extends beyond simple service interruption to potentially affect system stability and overall network performance, particularly in environments where multiple vulnerable services operate concurrently.
Mitigation strategies should focus on immediate code-level fixes where the recvn and sendn functions are modified to properly handle zero-byte returns from recv calls. The implementation should check for return values of zero and terminate the operation gracefully rather than continuing the loop. Additionally, proper timeout mechanisms and connection state monitoring should be implemented to prevent indefinite waiting conditions. System administrators should also consider implementing connection monitoring and automatic process restart mechanisms as defensive measures. The vulnerability highlights the importance of robust error handling in network programming and serves as a reminder of the critical need to validate all system call return values, particularly in security-sensitive network applications.