CVE-2001-1549 in Personal Firewall
Summary
by MITRE
Tiny Personal Firewall 1.0 and 2.0 allows local users to bypass filtering via non-standard TCP packets created with non-Windows protocol adapters.
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Analysis
by VulDB Data Team • 05/27/2025
The vulnerability described in CVE-2001-1549 represents a significant security flaw in Tiny Personal Firewall versions 1.0 and 2.0 that affects local users within the Windows operating system environment. This issue stems from the firewall implementation's inability to properly handle non-standard TCP packets that are generated through non-Windows protocol adapters, creating a pathway for unauthorized network traffic to bypass the intended filtering mechanisms. The flaw specifically targets the packet processing logic of the firewall software, which fails to adequately validate or inspect traffic that does not conform to standard Windows networking protocols.
The technical implementation of this vulnerability occurs at the network protocol level where the firewall software relies on standard Windows protocol adapter interfaces for packet inspection and filtering. When non-Windows protocol adapters are employed, these adapters generate TCP packets that follow different formatting conventions or use alternative protocol stacks that the Tiny Personal Firewall does not properly account for in its filtering logic. This creates a gap in the security model where packets bypass the normal inspection process, allowing malicious local users to establish connections or transmit data without the firewall's knowledge or control. The vulnerability essentially represents a failure in the firewall's protocol handling capabilities, specifically related to how it processes and validates network traffic that deviates from expected Windows networking standards.
From an operational perspective, this vulnerability poses a substantial risk to systems running Tiny Personal Firewall 1.0 or 2.0, as local users who have access to the system can exploit this weakness to circumvent network security controls. The impact extends beyond simple bypass of filtering mechanisms to potentially enable more sophisticated attacks such as port scanning, data exfiltration, or establishment of covert communication channels. Attackers could leverage this vulnerability to establish persistence within a network environment, particularly in scenarios where local access is already compromised, or to evade network monitoring systems that rely on the firewall for traffic control. The local nature of the attack means that exploitation requires physical or authenticated access to the target system, but the consequences can be severe as it undermines the fundamental security assumptions of the firewall protection model.
The vulnerability aligns with CWE-284, which addresses improper access control mechanisms, and reflects weaknesses in the firewall's packet validation and filtering implementation. From an attack perspective, this issue would be categorized under the ATT&CK technique T1068, which involves the exploitation of local system privileges to bypass security controls. The flaw demonstrates a classic case of incomplete input validation where the firewall software fails to account for protocol variations that could occur in non-standard network environments. Organizations should implement immediate mitigations including updating to patched versions of Tiny Personal Firewall, disabling the firewall if alternative security measures are in place, or implementing additional network monitoring to detect anomalous traffic patterns that might indicate exploitation attempts. The vulnerability also underscores the importance of comprehensive protocol testing and validation in security software to prevent such gaps in protection that could be exploited by determined attackers.