CVE-2005-1127 in Postgrey
Summary
by MITRE
Format string vulnerability in the log function in Net::Server 0.87 and earlier, as used in Postfix Greylisting Policy Server (Postgrey) 1.18 and earlier, and possibly other products, allows remote attackers to cause a denial of service (crash) via format string specifiers that are not properly handled before being sent to syslog, as demonstrated using sender addresses to Postgrey.
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Analysis
by VulDB Data Team • 06/24/2019
The vulnerability identified as CVE-2005-1127 represents a critical format string flaw within the logging functionality of Net::Server version 0.87 and earlier implementations. This vulnerability specifically affects the Postfix Greylisting Policy Server (Postgrey) version 1.18 and earlier, though it may extend to other products utilizing the same vulnerable library. The flaw manifests when the system processes sender addresses containing format string specifiers without proper sanitization before transmitting them to the syslog function. This particular vulnerability falls under the CWE-134 category, which specifically addresses format string vulnerabilities where format specifiers are derived from untrusted input sources.
The technical exploitation of this vulnerability occurs when remote attackers craft malicious sender addresses that contain format string specifiers such as %s, %d, or other format conversion characters. When these malformed addresses are processed by the vulnerable Postgrey implementation, the format specifiers are passed directly to the syslog function without proper validation or escaping. The syslog function interprets these specifiers as instructions for formatting additional arguments, which can lead to memory corruption, stack smashing, or arbitrary code execution depending on the specific implementation details. The vulnerability is particularly dangerous because it can be triggered through normal email communication flows, making it an attractive target for attackers seeking to disrupt mail services.
The operational impact of this vulnerability is significant as it enables remote attackers to perform denial of service attacks against systems running vulnerable versions of Postgrey. When exploited successfully, the vulnerability causes the Postgrey daemon to crash and terminate unexpectedly, leading to service disruption for email greylisting functionality. This disruption can result in legitimate emails being delayed or rejected, potentially affecting business communications and email deliverability. The attack vector is particularly concerning because it requires no authentication and can be executed through normal email submission processes, making it difficult to detect and prevent. The vulnerability also aligns with ATT&CK technique T1499.004, which covers network denial of service attacks, and T1070.006, covering indicator removal on host through log manipulation.
Mitigation strategies for CVE-2005-1127 involve immediate patching of affected systems to upgrade to versions of Net::Server and Postgrey that properly sanitize format string arguments before passing them to syslog functions. Organizations should implement input validation measures that strip or escape format specifiers from sender addresses before processing them in logging contexts. Network-level protections can include implementing rate limiting and connection filtering to reduce the impact of potential exploitation attempts. Additionally, system administrators should monitor for unusual daemon crashes and implement proper logging and alerting mechanisms to detect exploitation attempts. The vulnerability highlights the importance of secure coding practices and proper input validation, particularly when dealing with user-supplied data that may be passed to system functions that interpret format strings. Organizations should also consider implementing network segmentation and access controls to limit exposure of vulnerable services to untrusted networks.