CVE-2008-2735 in ASA 5500
Summary
by MITRE
The HTTP server in Cisco Adaptive Security Appliance (ASA) 5500 devices 8.0 before 8.0(3)15 and 8.1 before 8.1(1)5, when configured as a clientless SSL VPN endpoint, does not properly process URIs, which allows remote attackers to cause a denial of service (device reload) via a URI in a crafted SSL or HTTP packet, aka Bug ID CSCsq19369.
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Analysis
by VulDB Data Team • 08/16/2019
The vulnerability identified as CVE-2008-2735 affects Cisco Adaptive Security Appliance (ASA) 5500 series devices operating with specific software versions, creating a critical denial of service condition through improper URI handling within the HTTP server component. This flaw exists specifically when the ASA is configured as a clientless SSL VPN endpoint, making it particularly dangerous for organizations relying on secure remote access solutions. The vulnerability stems from the device's failure to properly validate and process Uniform Resource Identifiers within SSL or HTTP packets, allowing malicious actors to craft specially formatted packets that trigger unexpected behavior in the device's processing engine.
The technical implementation of this vulnerability occurs at the application layer where the ASA's HTTP server component receives and processes incoming packets containing URIs. When a malformed URI is received through a crafted SSL or HTTP packet, the device's processing logic fails to handle the input appropriately, leading to an uncontrolled state that ultimately results in a device reload or complete system restart. This behavior represents a classic buffer overflow or input validation vulnerability where the system does not properly sanitize incoming data before processing. The flaw specifically impacts versions 8.0 before 8.0(3)15 and 8.1 before 8.1(1)5, indicating that the issue was present in the core HTTP processing module of these particular software releases.
From an operational perspective, this vulnerability presents a severe risk to network availability and business continuity, as remote attackers can remotely trigger device reboots without requiring authentication or physical access. The impact extends beyond simple service disruption to potentially compromise the integrity of secure remote access infrastructure that organizations depend upon for business operations. Network administrators who have configured their ASA devices as clientless SSL VPN endpoints face the highest risk, as this functionality is commonly used for remote employee access, partner connectivity, and secure administrative access to internal resources. The vulnerability can be exploited from external networks, making it particularly dangerous for organizations with exposed ASA devices.
The mitigation strategy for this vulnerability involves immediate deployment of Cisco's security patches and software updates, specifically targeting the affected software versions mentioned in the advisory. Organizations should prioritize upgrading to versions 8.0(3)15 or 8.1(1)5, which contain the necessary code fixes to properly validate URI inputs and prevent the device from crashing. Network segmentation and access control measures should be implemented to limit exposure of vulnerable ASA devices to external networks, while monitoring systems should be configured to detect anomalous packet patterns that might indicate exploitation attempts. Additionally, organizations should consider implementing temporary workarounds such as disabling clientless SSL VPN functionality until proper patches can be deployed, aligning with the principle of least privilege and reducing the attack surface for this specific vulnerability.
This vulnerability maps directly to CWE-121, which describes buffer overflow conditions in heap-based memory allocation, and CWE-122, which covers buffer overflow conditions in stack-based memory allocation, as the improper URI handling likely causes memory corruption during packet processing. The attack pattern aligns with ATT&CK technique T1499.004, which involves network disruption through service availability attacks, specifically targeting denial of service conditions. The vulnerability also represents a failure in the CIA triad, specifically compromising availability by enabling unauthorized users to disrupt critical network services. Organizations should view this as a critical security issue requiring immediate attention, as the combination of remote exploitability and the potential for complete device restart makes it a high-priority vulnerability for remediation across all affected network infrastructure.