CVE-2003-0688 in Sendmail
Summary
by MITRE
The DNS map code in Sendmail 8.12.8 and earlier, when using the "enhdnsbl" feature, does not properly initialize certain data structures, which allows remote attackers to cause a denial of service (process crash) via an invalid DNS response that causes Sendmail to free incorrect data.
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Analysis
by VulDB Data Team • 12/26/2024
The vulnerability identified as CVE-2003-0688 represents a critical denial of service flaw within the Sendmail email server software, specifically affecting versions 8.12.8 and earlier. This issue resides within the DNS map code implementation that handles the "enhdnsbl" feature, which is designed to enhance DNS-based blackhole list functionality for spam filtering purposes. The vulnerability stems from improper initialization of data structures during DNS response processing, creating a condition where maliciously crafted DNS responses can trigger unexpected behavior in the mail server's memory management systems.
The technical flaw manifests when Sendmail processes DNS responses through the enhanced DNS blackhole list functionality. During normal operation, the software initializes data structures to store and manage DNS query results. However, due to inadequate initialization procedures, the system fails to properly set up memory pointers and data references when encountering malformed DNS responses. This improper initialization leads to a scenario where the software attempts to free memory locations that either do not contain valid data structures or have already been freed, resulting in memory corruption and subsequent process termination. The vulnerability operates at the intersection of memory management and network protocol handling, creating a pathway for remote attackers to exploit the software's response to malformed network data.
The operational impact of this vulnerability extends beyond simple service disruption, as it represents a fundamental flaw in the software's memory safety mechanisms. Attackers can leverage this vulnerability by crafting specially formatted DNS responses that, when processed by Sendmail, trigger the memory corruption conditions. The resulting denial of service affects the entire mail server functionality, potentially disrupting email services for organizations relying on Sendmail for their communication infrastructure. This vulnerability is particularly concerning because it requires no authentication or special privileges to exploit, making it accessible to any remote attacker with network access to the target system. The flaw demonstrates a classic buffer over-read condition that can be classified under CWE-457, representing uninitialized memory access that leads to system instability.
Mitigation strategies for CVE-2003-0688 primarily focus on immediate software updates and patches, as the vulnerability is resolved through proper initialization of data structures within the DNS map code. Organizations should prioritize upgrading to Sendmail versions that include the patched implementation of the enhdnsbl feature, ensuring that data structures are properly initialized before processing DNS responses. Additional defensive measures include implementing DNS query validation mechanisms, configuring proper network segmentation to limit exposure, and establishing monitoring protocols to detect unusual DNS traffic patterns. The vulnerability's exploitation aligns with ATT&CK technique T1499.004, which covers network denial of service attacks, and demonstrates how memory safety issues in server applications can create significant operational risks. Network administrators should also consider implementing rate limiting for DNS queries and establishing robust logging mechanisms to detect potential exploitation attempts, as the vulnerability represents a clear example of how improper input validation can lead to system instability and service disruption.