CVE-2005-0560 in Exchange
Summary
by MITRE
Heap-based buffer overflow in the SvrAppendReceivedChunk function in xlsasink.dll in the SMTP service of Exchange Server 2000 and 2003 allows remote attackers to execute arbitrary code via a crafted X-LINK2STATE extended verb request to the SMTP port.
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Analysis
by VulDB Data Team • 07/04/2025
The vulnerability identified as CVE-2005-0560 represents a critical heap-based buffer overflow flaw within the Microsoft Exchange Server 2000 and 2003 SMTP service implementations. This vulnerability specifically affects the svrappendreceivedchunk function located in the xlsasink.dll component, which processes incoming email messages through the SMTP protocol. The flaw manifests when the system receives a specially crafted X-LINK2STATE extended verb request, a mechanism that extends the standard smtp protocol to include additional functionality for link state information exchange. This particular vulnerability resides within the server-side processing logic that handles email message reception and processing, making it particularly dangerous as it can be exploited remotely without authentication.
The technical exploitation of this vulnerability occurs through manipulation of the heap memory allocation process during message processing. When the smtp service receives a malformed X-LINK2STATE extended verb request, the svrappendreceivedchunk function fails to properly validate the length of incoming data before copying it into a fixed-size buffer allocated on the heap. This improper bounds checking creates a condition where an attacker can overflow the allocated buffer space, potentially overwriting adjacent memory locations including function return addresses, stack canaries, or other critical program state information. The heap-based nature of this overflow means that the memory corruption can occur in unpredictable locations, making exploitation both more complex and more potentially devastating than stack-based buffer overflows.
The operational impact of this vulnerability extends far beyond simple denial of service scenarios, as it provides remote attackers with the capability to execute arbitrary code with the privileges of the exchange service account. This remote code execution vulnerability can be leveraged by attackers to gain complete control over affected mail servers, potentially leading to data exfiltration, persistent backdoor installation, or further lateral movement within network environments. The vulnerability affects organizations running Microsoft Exchange Server 2000 and 2003, which were widely deployed enterprise email solutions that often served as critical communication infrastructure for businesses and government organizations. The attack vector requires only a connection to the SMTP port, making it particularly dangerous as it can be exploited from anywhere on the internet without requiring any authentication credentials.
Security professionals should note that this vulnerability maps to CWE-121, which describes heap-based buffer overflow conditions where insufficient bounds checking allows attackers to overwrite heap memory. The attack pattern aligns with techniques documented in the ATT&CK framework under T1190 for exploitation of remote services and T1059 for execution through command and scripting interpreters. Organizations should prioritize immediate remediation through Microsoft security patches, as the vulnerability was widely exploited in the wild during 2005. Network segmentation and firewall rules should be implemented to restrict access to SMTP ports from untrusted networks, while monitoring should be enabled to detect anomalous X-LINK2STATE verb usage patterns. The vulnerability also highlights the importance of proper input validation and memory management practices in server-side applications, particularly those handling untrusted network data through extended protocol mechanisms.