CVE-2007-0720 in CUPS
Summary
by MITRE
The CUPS service on multiple platforms allows remote attackers to cause a denial of service (service hang) via a "partially-negotiated" SSL connection, which prevents other requests from being accepted.
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Analysis
by VulDB Data Team • 07/16/2019
The vulnerability identified as CVE-2007-0720 affects the Common Unix Printing System (CUPS) service across multiple platforms, representing a significant denial of service weakness that can be exploited remotely. This issue specifically targets the SSL/TLS connection handling mechanism within CUPS, where attackers can manipulate the negotiation process to create a state where the service becomes unresponsive. The flaw occurs during the SSL handshake phase when connections are not properly terminated or managed, leading to a condition where the service remains in a partially negotiated state and cannot process subsequent incoming requests.
The technical root cause of this vulnerability lies in the improper handling of SSL connection states within the CUPS printing service implementation. When an attacker establishes an SSL connection but fails to complete the negotiation process properly, the service maintains this incomplete connection in memory without properly releasing the associated resources or rejecting the connection. This creates a resource exhaustion scenario where the service becomes unable to accept new legitimate connection requests, effectively causing a denial of service condition. The vulnerability is classified under CWE-400 as an Uncontrolled Resource Consumption, specifically involving improper handling of network connections and protocol states.
From an operational perspective, this vulnerability presents a serious risk to organizations that rely on CUPS for printing services, particularly in environments where remote access is permitted or where the service is exposed to untrusted networks. The impact extends beyond simple service interruption as it can affect business operations that depend on print services, potentially causing delays in document processing workflows and disrupting productivity. Attackers can exploit this weakness with minimal resources, requiring only the ability to establish network connections to the CUPS service port, typically port 631. The vulnerability affects multiple operating systems including various unix-like systems and Linux distributions where CUPS is installed.
The attack vector for this vulnerability aligns with ATT&CK technique T1499.004 which involves network denial of service attacks. This weakness can be exploited through a simple network-based attack where an attacker establishes a connection to the CUPS service and then abandons the SSL negotiation process without completing it. The service remains blocked in a processing state, unable to handle additional requests until the hung connection times out or is manually cleared. This makes the vulnerability particularly dangerous in environments where CUPS is configured to accept connections from external networks or where network access controls are insufficient.
Organizations should implement immediate mitigations including updating to patched versions of CUPS where the SSL connection handling has been corrected to properly terminate incomplete negotiations. Network segmentation and access controls should be enforced to limit exposure of the CUPS service to trusted networks only. Additionally, implementing connection rate limiting and monitoring for unusual connection patterns can help detect exploitation attempts. System administrators should also consider configuring the service to use shorter timeouts for incomplete SSL negotiations and implement proper resource management to prevent the accumulation of hung connections. The vulnerability demonstrates the importance of robust protocol implementation and proper resource cleanup in network services, particularly those handling secure communications.