CVE-2005-2317 in Shorewall
Summary
by MITRE
Shorewall 2.4.x before 2.4.1, 2.2.x before 2.2.5, and 2.0.x before 2.0.17, when MACLIST_TTL is greater than 0 or MACLIST_DISPOSITION is set to ACCEPT, allows remote attackers with an accepted MAC address to bypass other firewall rules or policies.
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Analysis
by VulDB Data Team • 06/07/2019
The vulnerability identified as CVE-2005-2317 affects Shorewall versions prior to specific patches, creating a significant security flaw in network firewall configurations that can be exploited by remote attackers. Shorewall serves as a powerful tool for managing iptables firewall rules on linux systems, providing a higher-level interface for complex network security policies. This particular vulnerability resides in the handling of MAC address lists within the firewall configuration, specifically when certain parameters are configured to allow for MAC address acceptance. The flaw becomes particularly dangerous when the MACLIST_TTL parameter is set to a value greater than zero or when MACLIST_DISPOSITION is configured to ACCEPT, creating conditions where attackers can manipulate their network access through legitimate MAC addresses.
The technical implementation of this vulnerability stems from improper validation and enforcement of firewall rules when MAC address lists are utilized in Shorewall configurations. When MACLIST_TTL is greater than zero, the system maintains cached MAC address entries for a specified time period, and when MACLIST_DISPOSITION is set to ACCEPT, the firewall rules permit traffic from MAC addresses that have been accepted into the list. Attackers who can obtain or manipulate a valid MAC address that has been accepted by the firewall can bypass subsequent firewall rules and policies that should normally block their traffic. This represents a fundamental flaw in the rule evaluation order and enforcement mechanism within Shorewall's MAC address handling logic, where accepted MAC addresses can effectively create a backdoor that circumvents normal security controls.
The operational impact of this vulnerability extends beyond simple network access bypass, as it can enable attackers to gain unauthorized access to protected network resources and services. Remote attackers who possess a MAC address that has been accepted by the firewall can potentially traverse network boundaries that should remain protected, effectively undermining the layered security approach that organizations rely upon. The vulnerability becomes particularly concerning in environments where Shorewall is used to enforce strict network segmentation policies or where MAC address filtering is implemented as part of a broader security strategy. This flaw essentially allows attackers to create persistent access paths that can bypass multiple layers of network security controls, potentially leading to data breaches, unauthorized system access, or further exploitation within the network.
Organizations using affected Shorewall versions should immediately implement mitigations including updating to patched versions of Shorewall, specifically versions 2.4.1, 2.2.5, and 2.0.17 or later. Configuration changes should be made to avoid setting MACLIST_TTL greater than zero or using MACLIST_DISPOSITION set to ACCEPT unless absolutely necessary. The vulnerability aligns with CWE-284, which addresses improper access control, and represents a clear violation of the principle of least privilege in network security. From an ATT&CK framework perspective, this vulnerability maps to techniques involving privilege escalation and persistence, as attackers can establish unauthorized access paths that bypass normal network security controls. Additionally, the flaw demonstrates characteristics of credential reuse and network infiltration tactics, as attackers can leverage accepted MAC addresses to maintain access without requiring additional authentication credentials or exploiting other system vulnerabilities.