CVE-2001-0026 in rp-pppoe
Summary
by MITRE
rp-pppoe PPPoE client allows remote attackers to cause a denial of service via the Clamp MSS option and a TCP packet with a zero-length TCP option.
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Analysis
by VulDB Data Team • 09/26/2024
The vulnerability identified as CVE-2001-0026 resides within the rp-pppoe PPPoE client implementation, specifically targeting the handling of TCP packet options during PPPoE session establishment. This flaw represents a classic denial of service vulnerability that exploits the improper processing of network packets containing malformed TCP options. The rp-pppoe client is commonly used in broadband internet connections to establish point-to-point protocol over ethernet sessions, making this vulnerability particularly impactful in residential and small business networking environments. The vulnerability manifests when the client receives a TCP packet with a zero-length TCP option, which triggers an improper handling mechanism within the packet processing pipeline. This issue stems from insufficient input validation and lack of proper bounds checking during the parsing of TCP options within the PPPoE client stack.
The technical exploitation of this vulnerability occurs through the Clamp MSS option, which is a TCP option used to control the maximum segment size in TCP connections. When an attacker crafts a TCP packet with a zero-length TCP option and includes the Clamp MSS option, the rp-pppoe client fails to properly validate the option length field. This parsing error causes the client to enter an undefined state where it cannot properly process subsequent packets or maintain the PPPoE session. The vulnerability maps to CWE-129, which describes improper validation of length fields, and CWE-691, which covers insufficient control of a resource through public interfaces. The flaw demonstrates poor input sanitization and lacks proper error handling mechanisms that would normally prevent malformed data from disrupting normal operation.
The operational impact of this vulnerability extends beyond simple service disruption, as it can effectively terminate PPPoE sessions and render network connectivity unavailable to end users. Attackers can exploit this weakness to repeatedly cause service interruptions, potentially leading to extended outages that affect internet access for multiple users sharing the same network infrastructure. The vulnerability is particularly concerning because it requires minimal network access to exploit and can be automated, making it a viable attack vector for persistent disruption campaigns. This type of denial of service attack can be classified under the ATT&CK technique T1499.004, which covers network disruption through service exhaustion or corruption, and represents a form of resource exhaustion that impacts network availability.
Mitigation strategies for CVE-2001-0026 should focus on implementing proper input validation and bounds checking within the rp-pppoe client implementation. Network administrators should ensure that all PPPoE client software is updated to versions that properly validate TCP option lengths before processing them. The implementation should include defensive programming practices such as checking option length fields against expected values and implementing proper error handling for malformed packets. Additionally, network segmentation and firewall rules can be configured to filter out suspicious TCP packets with zero-length options before they reach the PPPoE client. The vulnerability highlights the importance of robust input validation and proper error handling in network protocol implementations, as outlined in the OWASP Top Ten 2017 category A03: Injection, which emphasizes the need for proper validation of all inputs to prevent exploitation of parsing vulnerabilities. Organizations should also consider implementing intrusion detection systems that can identify and alert on anomalous TCP packet patterns that may indicate exploitation attempts.