CVE-2011-1764 in exim
Summary
by MITRE
Format string vulnerability in the dkim_exim_verify_finish function in src/dkim.c in Exim before 4.76 might allow remote attackers to execute arbitrary code or cause a denial of service (daemon crash) via format string specifiers in data used in DKIM logging, as demonstrated by an identity field containing a % (percent) character.
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Analysis
by VulDB Data Team • 11/23/2021
The CVE-2011-1764 vulnerability represents a critical format string flaw in the Exim mail transfer agent that affects versions prior to 4.76. This vulnerability specifically resides within the dkim_exim_verify_finish function located in the src/dkim.c source file, making it particularly dangerous as it targets the DomainKeys Identified Mail verification functionality that is integral to email security. The flaw occurs when the DKIM logging mechanism processes data containing format string specifiers, creating a potential attack vector that can be exploited by remote adversaries to gain unauthorized system access or disrupt service availability.
The technical implementation of this vulnerability stems from improper input validation and handling within the DKIM verification logging process. When the dkim_exim_verify_finish function processes email data that contains percent characters, these characters are interpreted as format string specifiers rather than literal data. This misinterpretation allows attackers to inject malicious format specifiers that can manipulate the program's memory layout, potentially leading to arbitrary code execution or daemon crashes. The vulnerability is particularly insidious because it leverages legitimate DKIM verification functionality to deliver malicious payloads, making detection more challenging for security monitoring systems.
The operational impact of this vulnerability extends beyond simple denial of service scenarios to encompass full system compromise capabilities. Remote attackers can exploit this flaw to execute arbitrary code with the privileges of the Exim daemon process, potentially leading to complete system compromise and unauthorized access to email infrastructure. The vulnerability also enables denial of service attacks that can crash the Exim daemon, effectively disrupting email services for organizations relying on this mail transfer agent. Organizations using affected Exim versions face significant risk as the vulnerability can be exploited through normal email traffic without requiring special privileges or authentication.
Security mitigations for CVE-2011-1764 primarily focus on immediate patching and version updates to Exim 4.76 or later releases that contain the necessary fixes. System administrators should prioritize upgrading their Exim installations to prevent exploitation, as this vulnerability has been widely documented and exploited in the wild. Additional protective measures include implementing strict input validation for DKIM-related email data, monitoring for unusual logging patterns that might indicate exploitation attempts, and configuring proper network segmentation to limit potential attack surfaces. From a cybersecurity framework perspective, this vulnerability aligns with CWE-134 which specifically addresses format string vulnerabilities, and maps to ATT&CK techniques involving privilege escalation and remote code execution through software vulnerabilities. Organizations should also consider implementing intrusion detection systems capable of identifying format string exploitation patterns and maintain comprehensive backup and recovery procedures to address potential service disruptions caused by this vulnerability.