CVE-2001-0819 in Fetchmail
Summary
by MITRE
A buffer overflow in Linux fetchmail before 5.8.6 allows remote attackers to execute arbitrary code via a large To: field in an email header.
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Analysis
by VulDB Data Team • 07/19/2019
The vulnerability identified as CVE-2001-0819 represents a critical buffer overflow flaw in the fetchmail utility, a widely used email retrieval client for unix-like systems. This vulnerability specifically affects fetchmail versions prior to 5.8.6 and exposes systems to remote code execution attacks through carefully crafted email headers. The flaw manifests when the utility processes email messages containing excessively long To: fields in the message headers, creating a condition where memory allocated for header parsing exceeds its intended boundaries.
The technical nature of this vulnerability aligns with CWE-121, which categorizes buffer overflow conditions where insufficient bounds checking allows attackers to overwrite adjacent memory locations. In fetchmail's case, the buffer overflow occurs during the parsing of email headers, specifically when handling the To: field which can be manipulated by remote attackers to exceed the allocated buffer space. This type of vulnerability falls under the broader category of stack-based buffer overflows as described in the ATT&CK framework under technique T1059.007 for command and scripting interpreter, where malicious code execution can be achieved through memory corruption.
The operational impact of this vulnerability extends beyond simple remote code execution, as it enables attackers to potentially gain full control over systems running vulnerable fetchmail versions. Since fetchmail is commonly used to retrieve emails from remote mail servers and deliver them locally, attackers can exploit this vulnerability by simply sending a specially crafted email message to a target system. The attack vector is particularly dangerous because it requires no authentication and can be executed against any system running an affected version of fetchmail, making it a prime target for automated exploitation campaigns. Systems that rely on fetchmail for email retrieval are at significant risk, particularly those in enterprise environments where email processing is a critical function.
Mitigation strategies for this vulnerability require immediate patching of fetchmail installations to version 5.8.6 or later, which contains the necessary fixes for the buffer overflow condition. Organizations should also implement email filtering mechanisms that can detect and block unusually long header fields, though this represents a secondary defense measure. Network administrators should consider implementing email security solutions that can scan incoming messages for potentially malicious header structures, and monitoring systems should be configured to detect unusual email processing patterns that might indicate exploitation attempts. The vulnerability serves as a reminder of the importance of keeping email processing utilities updated and demonstrates how seemingly simple header parsing functions can create critical security risks when proper bounds checking is not implemented. Additionally, system administrators should consider implementing defensive programming practices such as using safer string handling functions and enabling stack protection mechanisms to reduce the impact of similar vulnerabilities that may exist in other components of the email infrastructure.