CVE-2018-0353 in Web Security Appliance
Summary
by MITRE
A vulnerability in traffic-monitoring functions in Cisco Web Security Appliance (WSA) could allow an unauthenticated, remote attacker to circumvent Layer 4 Traffic Monitor (L4TM) functionality and bypass security protections. The vulnerability is due to a change in the underlying operating system software that is responsible for monitoring affected traffic. An attacker could exploit this vulnerability by sending crafted IP packets to an affected device. A successful exploit could allow the attacker to pass traffic through the device, which the WSA was configured to deny. This vulnerability affects both IPv4 and IPv6 traffic. This vulnerability affects Cisco AsyncOS versions for WSA on both virtual and hardware appliances running any release of the 10.5.1, 10.5.2, or 11.0.0 WSA Software. The WSA is vulnerable if it is configured for L4TM. Cisco Bug IDs: CSCvg78875.
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Analysis
by VulDB Data Team • 03/22/2023
The vulnerability described in CVE-2018-0353 represents a critical flaw in Cisco Web Security Appliance traffic monitoring capabilities that fundamentally undermines the device's security posture. This weakness specifically targets the Layer 4 Traffic Monitor (L4TM) functionality, which serves as a crucial component for enforcing network access controls and traffic filtering policies. The vulnerability arises from modifications within the underlying operating system software that governs how the WSA processes and monitors network traffic, creating an unexpected pathway for malicious actors to bypass established security measures. The attack vector is particularly concerning as it requires no authentication and can be executed remotely, making it accessible to any attacker with network connectivity to the affected device. The flaw affects both IPv4 and IPv6 traffic streams, indicating a comprehensive impact across the device's network monitoring capabilities. This vulnerability is particularly dangerous because it directly compromises the core security function of the appliance, allowing malicious traffic to pass through devices that were explicitly configured to block such communications.
The technical exploitation of this vulnerability stems from the modification of the underlying operating system components responsible for traffic monitoring, which creates a condition where crafted IP packets can manipulate the L4TM functionality. Attackers can leverage this weakness by sending specifically constructed packets that exploit the altered system behavior, effectively disabling or circumventing the traffic monitoring mechanisms. The vulnerability affects Cisco AsyncOS versions running on both virtual and physical hardware appliances, indicating that the issue is not limited to a specific deployment model. The affected software versions include 10.5.1, 10.5.2, and 11.0.0 releases, which suggests that this flaw was present across a significant portion of the WSA software lineage. The fact that the vulnerability requires L4TM configuration to be active means that organizations with this feature enabled are particularly at risk, as the security controls they rely on become ineffective. The Cisco bug ID CSCvg78875 indicates that this was recognized as a specific software regression rather than a fundamental architectural flaw, suggesting that the issue resulted from a code change that inadvertently compromised the monitoring functionality.
The operational impact of this vulnerability extends far beyond simple traffic bypassing, as it fundamentally compromises the integrity of network security policies enforced by the WSA appliance. Organizations that depend on L4TM for controlling traffic flow and enforcing access restrictions face a significant risk of unauthorized access to their networks, as malicious actors can now pass through devices configured to block specific traffic patterns. This vulnerability essentially allows attackers to establish persistent unauthorized communication channels through the network perimeter, potentially enabling data exfiltration, command and control communications, or other malicious activities. The remote nature of the attack means that threat actors do not require physical access or network proximity to exploit the vulnerability, making it particularly dangerous in environments where network security is paramount. The cross-protocol impact affecting both IPv4 and IPv6 traffic ensures that organizations cannot rely on protocol-specific mitigations, and the vulnerability affects both virtual and hardware deployments, creating a broad attack surface. This weakness directly violates the principle of least privilege and can lead to complete bypass of network security controls that organizations depend upon for protecting their infrastructure.
Organizations affected by this vulnerability should implement immediate mitigations while awaiting official patches from Cisco, as the risk of exploitation remains high. The primary mitigation strategy involves disabling L4TM functionality on affected appliances until a security update is applied, though this may impact legitimate traffic monitoring capabilities. Network segmentation and additional monitoring controls should be implemented to detect anomalous traffic patterns that might indicate exploitation attempts. Security teams should also review their current traffic monitoring configurations to identify any potential bypasses that may have occurred during the vulnerability window. The remediation process requires careful planning to ensure that network security policies remain intact while addressing the specific operating system modification that introduced the vulnerability. Organizations should also conduct comprehensive security assessments to identify any unauthorized access or data compromise that may have occurred during the vulnerability exposure period. This vulnerability highlights the importance of maintaining strict control over operating system updates and the potential security implications of underlying software changes. The incident underscores the need for robust security testing procedures and the importance of understanding how system modifications can affect security controls. From a compliance perspective, this vulnerability may trigger regulatory reporting requirements and could impact security audit outcomes, as it represents a significant weakness in the network security infrastructure. The vulnerability also demonstrates the critical importance of maintaining current security patches and the potential consequences of delayed updates in security-critical network appliances.