CVE-2004-0918 in Squid
Summary
by MITRE
The asn_parse_header function (asn1.c) in the SNMP module for Squid Web Proxy Cache before 2.4.STABLE7 allows remote attackers to cause a denial of service (server restart) via certain SNMP packets with negative length fields that trigger a memory allocation error.
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Analysis
by VulDB Data Team • 06/29/2019
The vulnerability identified as CVE-2004-0918 represents a critical memory handling flaw within the SNMP module of Squid Web Proxy Cache versions prior to 2.4.STABLE7. This issue manifests in the asn_parse_header function located in the asn1.c file, where improper validation of SNMP packet structures creates a pathway for remote attackers to exploit the system. The vulnerability specifically targets the handling of negative length fields within SNMP packets, which are commonly used in ASN.1 (Abstract Syntax Notation One) encoded data structures that form the foundation of SNMP communications. When the function encounters such malformed packets containing negative length values, it attempts to allocate memory based on these invalid parameters, leading to unpredictable behavior and system instability.
The technical exploitation of this vulnerability occurs through the manipulation of SNMP packet headers where attackers craft malicious packets with negative length fields that bypass normal validation checks. This flaw falls under the CWE-129 weakness category, which encompasses issues related to improper validation of array indices and memory allocation parameters. The vulnerability operates at the protocol parsing layer where SNMP requests are processed, making it particularly dangerous as it can be triggered by any remote system communicating with the Squid proxy server. The memory allocation error occurs when the system attempts to allocate heap memory based on the negative length values, often resulting in memory corruption or allocation failures that ultimately cause the proxy server to crash and restart automatically.
From an operational perspective, this vulnerability presents a significant denial of service risk for organizations relying on Squid as their primary web proxy solution. The impact extends beyond simple service interruption as the automatic server restart can disrupt ongoing network operations, potentially affecting thousands of users simultaneously. The attack vector is particularly concerning because it requires no authentication or specialized privileges, making it accessible to any remote attacker who can send SNMP packets to the vulnerable system. Network administrators may experience unexpected service outages and increased system maintenance overhead as the proxy server repeatedly restarts due to these crafted malicious packets. This vulnerability also demonstrates the importance of proper input validation in network protocol implementations, as the lack of bounds checking on length fields creates a direct pathway for memory corruption.
Organizations affected by this vulnerability should prioritize immediate patching of their Squid installations to version 2.4.STABLE7 or later, which contains the necessary fixes for proper length field validation. The mitigation strategy should also include implementing network-level filtering to restrict SNMP traffic to trusted sources only, thereby reducing the attack surface. Security monitoring should be enhanced to detect unusual patterns of SNMP traffic that might indicate exploitation attempts, particularly looking for malformed packets with negative length fields. Additionally, system administrators should consider implementing intrusion detection systems that can identify and alert on specific patterns of SNMP packet structures that match the vulnerability characteristics. The fix implemented in the patched versions typically involves adding proper validation checks for length parameters before memory allocation occurs, ensuring that negative or excessively large values are rejected before processing. This vulnerability serves as a reminder of the critical importance of robust input validation in network services and aligns with ATT&CK technique T1499.004 for network denial of service attacks, where adversaries leverage protocol parsing flaws to cause system disruptions.