CVE-2001-1387 in Iptables
Summary
by MITRE
iptables-save in iptables before 1.2.4 records the "--reject-with icmp-host-prohibited" rule as "--reject-with tcp-reset," which causes iptables to generate different responses than specified by the administrator, possibly leading to an information leak.
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Analysis
by VulDB Data Team • 06/04/2018
The vulnerability identified as CVE-2001-1387 resides within the iptables packet filtering framework, specifically affecting versions prior to 1.2.4. This issue manifests in the iptables-save utility which is responsible for saving firewall rules to a file for later restoration. The flaw represents a critical discrepancy between the intended rule configuration and the actual implementation, creating a potential security risk through improper rule handling.
The technical flaw occurs when iptables-save processes rules containing the "--reject-with icmp-host-prohibited" specification. Instead of preserving the original rule specification, the utility incorrectly transforms this rule into "--reject-with tcp-reset" during the save operation. This transformation creates a fundamental mismatch between what the administrator intends to implement and what actually gets stored and subsequently applied by the system. The issue demonstrates a clear case of improper input handling and rule translation within the iptables framework.
The operational impact of this vulnerability extends beyond simple rule misapplication, potentially exposing systems to information leakage and unintended network behavior. When administrators configure their firewalls to reject connections with ICMP host prohibited messages, they expect specific network responses that provide appropriate feedback to connecting hosts. However, the incorrect transformation to TCP reset responses alters the network behavior in ways that may inadvertently reveal system information or create unexpected connection handling patterns. This misconfiguration can lead to scenarios where network reconnaissance becomes easier for attackers, as the altered responses may provide additional information about the network topology or system configuration.
The vulnerability aligns with CWE-1004, which addresses improper handling of input during rule processing, and demonstrates characteristics consistent with CWE-778, focusing on insufficient logging or monitoring of security-relevant events. From an adversarial perspective, this issue corresponds to ATT&CK technique T1082, which involves discovery of system information, as attackers could potentially exploit the altered network responses to gather more information about the target system. The improper rule handling creates a situation where network defenders cannot rely on their configured rules to function as intended, undermining the fundamental security posture of the system.
Mitigation strategies for this vulnerability require immediate upgrading of iptables to version 1.2.4 or later, where the rule translation issue has been resolved. System administrators should conduct thorough audits of existing firewall configurations to identify any rules that may have been affected by this transformation. Additionally, implementing proper monitoring of network responses and connection handling can help detect when the incorrect TCP reset behavior is occurring. Organizations should also establish procedures for regularly updating security tools and maintaining awareness of known vulnerabilities in network infrastructure components. The fix implemented in version 1.2.4 addresses the root cause by ensuring proper handling of the icmp-host-prohibited specification during rule saving operations, restoring the expected behavior and maintaining the integrity of firewall configurations.