CVE-2004-1002 in pppd
Summary
by MITRE
Integer underflow in pppd in cbcp.c for ppp 2.4.1 allows remote attackers to cause a denial of service (daemon crash) via a CBCP packet with an invalid length value that causes pppd to access an incorrect memory location.
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Analysis
by VulDB Data Team • 03/10/2021
The vulnerability identified as CVE-2004-1002 represents a critical integer underflow condition within the Point-to-Point Protocol daemon pppd version 2.4.1 specifically in the cbcp.c module. This flaw occurs during the processing of Control Block Compression Protocol packets, which are used in PPP connections to compress control information. The integer underflow manifests when pppd encounters a CBCP packet containing an invalid length field value that is smaller than the expected minimum size for such packets. This condition creates a scenario where the software performs arithmetic operations that result in negative integer values, which then get used as array indices or memory offsets, leading to unpredictable memory access patterns.
The technical implementation of this vulnerability stems from improper input validation within the packet processing logic of pppd. When the daemon receives a malformed CBCP packet with a length field that triggers the underflow condition, it calculates memory addresses based on this invalid value, causing the program to attempt to access memory locations outside the intended boundaries. This memory corruption can result in segmentation faults or other memory access violations that ultimately cause the pppd daemon to crash and terminate its operation. The vulnerability is classified under CWE-191 as an Integer Underflow (Wrap or Wraparound) and can be mapped to ATT&CK technique T1499.002 for Network Denial of Service, as it directly enables remote attackers to disrupt network services through daemon termination.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise the stability of network connections that rely on PPP for communication. When pppd crashes due to this condition, it affects all active PPP connections managed by that daemon instance, which can be particularly devastating in environments where PPP is used for critical network infrastructure such as dial-up access servers, broadband connections, or remote access services. The remote nature of the attack means that an unauthenticated attacker can exploit this vulnerability from outside the network perimeter, making it a significant threat vector for network administrators. Attackers can craft malicious CBCP packets with carefully constructed length fields to trigger the underflow condition and cause the daemon to crash repeatedly, leading to sustained denial of service conditions that can persist until the daemon is manually restarted or the system is rebooted.
Mitigation strategies for CVE-2004-1002 should focus on immediate patching of affected pppd installations with versions that contain proper input validation and bounds checking for CBCP packet length fields. Network administrators should also implement defensive measures such as packet filtering rules that can identify and drop malformed CBCP packets at network boundaries, particularly in environments where PPP services are exposed to untrusted networks. The implementation of intrusion detection systems that monitor for unusual patterns of PPP packet processing and daemon crashes can provide early warning of exploitation attempts. Additionally, organizations should consider disabling CBCP compression when it is not required for their network services, as this reduces the attack surface by eliminating the specific code path that contains the vulnerability. Regular security assessments of network infrastructure components and maintaining updated security patches form the cornerstone of protecting against this type of integer underflow vulnerability that can lead to unauthorized service disruption.