CVE-2002-0339 in IOS
Summary
by MITRE
Cisco IOS 11.1CC through 12.2 with Cisco Express Forwarding (CEF) enabled includes portions of previous packets in the padding of a MAC level packet when the MAC packet s length is less than the IP level packet length.
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Analysis
by VulDB Data Team • 09/19/2025
This vulnerability exists in Cisco IOS versions 11.1CC through 12.2 where Cisco Express Forwarding (CEF) is enabled, creating a significant security flaw in the network packet processing mechanism. The issue manifests when MAC level packets are smaller than their corresponding IP level packets, causing the system to include portions of previous packets within the padding of the current MAC packet. This behavior represents a violation of the expected packet structure and can lead to unpredictable network behavior. The vulnerability stems from improper handling of packet boundaries during the forwarding process, where the system fails to properly isolate packet contents when padding is required. This flaw falls under CWE-129, Input Validation, and specifically relates to improper handling of packet data structures in network processing. The issue is particularly concerning because it operates at the MAC layer, affecting how packets are transmitted and received across the network infrastructure.
The operational impact of this vulnerability extends beyond simple packet corruption, as it can potentially enable attackers to manipulate network traffic or extract information from packet contents. When previous packet data becomes embedded within padding, it creates opportunities for information leakage and can be exploited to reconstruct sensitive portions of network communications. Network devices processing these malformed packets may experience unexpected behavior, including potential crashes or inconsistent packet forwarding decisions. The vulnerability affects the fundamental integrity of packet transmission, undermining the security assumptions that network infrastructure relies upon for proper operation. Attackers could potentially leverage this weakness to perform packet injection attacks or to craft malicious traffic patterns that exploit the improper padding behavior. This issue particularly impacts network performance and reliability, as the malformed packets may cause retransmissions or require additional processing overhead to handle the unexpected data inclusion.
Mitigation strategies for this vulnerability should focus on disabling Cisco Express Forwarding when it is not essential for network operations, as this directly addresses the root cause of the issue. Network administrators should also consider upgrading to newer IOS versions where this vulnerability has been resolved, as Cisco has addressed similar packet handling issues in subsequent releases. Implementing proper network segmentation and monitoring can help detect anomalous packet behavior that might indicate exploitation attempts. Additionally, configuring network devices to enforce strict packet validation rules can prevent the propagation of malformed packets through the network infrastructure. Organizations should conduct thorough network audits to identify all affected devices and implement appropriate security controls. The mitigation approach aligns with ATT&CK technique T1071.004 for Application Layer Protocol: DNS, as it involves network protocol manipulation and can be used to establish persistent access through malformed traffic patterns. Regular security assessments and network traffic analysis should be performed to ensure that the vulnerability remains properly mitigated and to detect any potential exploitation attempts.