CVE-2002-0906 in Solaris
Summary
by MITRE
Buffer overflow in Sendmail before 8.12.5, when configured to use a custom DNS map to query TXT records, allows remote attackers to cause a denial of service and possibly execute arbitrary code via a malicious DNS server.
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Analysis
by VulDB Data Team • 09/11/2025
The vulnerability identified as CVE-2002-0906 represents a critical buffer overflow flaw in Sendmail versions prior to 8.12.5 that specifically manifests when the mail server is configured to utilize custom DNS maps for querying TXT records. This issue resides within the DNS resolution processing mechanism of Sendmail, where improper bounds checking occurs during the handling of DNS responses. The vulnerability is particularly concerning because it can be exploited remotely through malicious DNS servers, making it accessible to attackers without requiring local system access or authentication credentials.
The technical exploitation of this vulnerability occurs when Sendmail processes DNS TXT record queries through custom DNS maps, which are typically configured in the sendmail configuration files using the DNSMAP feature. When a malicious DNS server responds to a TXT record query with an oversized response, the buffer allocated within Sendmail's DNS processing code fails to properly validate the response length before copying data into the fixed-size buffer. This classic buffer overflow condition allows attackers to overwrite adjacent memory locations, potentially leading to arbitrary code execution or system crashes. The vulnerability specifically affects the DNS query processing functions that handle TXT record responses, where the implementation does not adequately check the length of incoming DNS data against the allocated buffer size.
From an operational perspective, this vulnerability presents a significant risk to email server infrastructure as it can be exploited to cause denial of service attacks by crashing the Sendmail process, effectively preventing legitimate email delivery and potentially disrupting business communications. The remote exploit capability means that attackers can target vulnerable systems from anywhere on the network without requiring physical access or network proximity. The potential for arbitrary code execution adds an additional layer of risk, as successful exploitation could allow attackers to gain control of the mail server, potentially leading to data exfiltration, spam relay capabilities, or further network infiltration. Organizations running Sendmail versions before 8.12.5 are particularly vulnerable since the flaw affects the core DNS resolution functionality that many email servers depend upon for various operational tasks including SPF record validation and other DNS-based email authentication mechanisms.
The vulnerability maps directly to CWE-121, which describes heap-based buffer overflow conditions, and aligns with ATT&CK technique T1190 for exploitation of remote services. Organizations should immediately upgrade to Sendmail version 8.12.5 or later, which includes proper bounds checking for DNS response handling. Additional mitigations include implementing DNS filtering mechanisms to prevent responses from untrusted DNS servers, configuring access controls to limit DNS query sources, and monitoring for unusual DNS query patterns that might indicate exploitation attempts. Network segmentation and firewall rules can help limit the attack surface by restricting access to DNS servers from potentially malicious sources. The fix implemented in Sendmail 8.12.5 addresses the root cause by ensuring proper validation of DNS response lengths before buffer copying operations, thereby preventing the overflow condition that enables both denial of service and arbitrary code execution scenarios.