CVE-2015-8078 in IMAP
Summary
by MITRE
Integer overflow in the index_urlfetch function in imap/index.c in Cyrus IMAP 2.3.19, 2.4.18, and 2.5.6 allows remote attackers to have unspecified impact via vectors related to urlfetch range checks and the section_offset variable. NOTE: this vulnerability exists because of an incomplete fix for CVE-2015-8076.
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Analysis
by VulDB Data Team • 06/28/2022
The vulnerability identified as CVE-2015-8078 represents a critical integer overflow condition within the Cyrus IMAP server software that affects versions 2.3.19, 2.4.18, and 2.5.6. This flaw specifically resides in the index_urlfetch function located in the imap/index.c source file, where improper handling of range checks and the section_offset variable creates opportunities for remote exploitation. The vulnerability is particularly concerning as it stems from an incomplete remediation of a previous vulnerability CVE-2015-8076, indicating a pattern of insufficient security fixes that leave systems exposed to continued exploitation. The integer overflow occurs when processing URL fetch operations within the IMAP protocol implementation, where maliciously crafted input can cause arithmetic operations to wrap around and produce unexpectedly large values. This type of vulnerability falls under CWE-190, which specifically addresses integer overflow conditions, and represents a classic example of how security patches that do not thoroughly address all attack vectors can leave systems vulnerable to exploitation. The operational impact of this vulnerability extends beyond simple denial of service scenarios, as it can potentially allow attackers to manipulate memory structures, bypass access controls, or execute arbitrary code within the context of the IMAP server process. When remote attackers exploit this condition, they can manipulate the section_offset variable to create invalid memory access patterns that may lead to heap corruption or other memory safety violations. The vulnerability demonstrates how seemingly minor issues in protocol handling can create significant security risks, particularly in server applications that process untrusted input from network clients. This flaw aligns with ATT&CK technique T1210, which covers exploitation of remote services through manipulation of input parameters, and represents a common vector for privilege escalation or data compromise in email server environments. The integer overflow condition specifically affects how the IMAP server handles URL fetch requests, where the server calculates offsets and ranges for content retrieval, and when these calculations overflow, they can result in unauthorized access to memory regions or execution of unintended code paths.
The technical implementation of this vulnerability involves the improper validation of integer values during URL fetch operations within the IMAP protocol handling code. When the index_urlfetch function processes requests, it performs calculations involving the section_offset variable that can exceed the maximum representable value for the integer type being used. This overflow condition can occur during range validation checks where the server attempts to determine valid boundaries for URL content retrieval. The incomplete fix for CVE-2015-8076 suggests that developers may have addressed some aspects of the vulnerability while leaving other attack vectors unpatched, creating a false sense of security. This pattern of partial remediation is particularly dangerous as it allows threat actors to identify alternative exploitation paths that were not addressed in the initial patch. The vulnerability is particularly insidious because it operates within the core protocol handling logic of the IMAP server, making it difficult to detect through standard network monitoring or intrusion detection systems. The impact of successful exploitation can range from service disruption to complete system compromise, depending on the specific circumstances and the privileges of the IMAP server process. Security researchers have noted that integer overflows in server applications often provide attackers with opportunities to manipulate program flow, bypass security checks, or access sensitive memory locations that could contain authentication credentials or other confidential information. The vulnerability's persistence across multiple minor versions of the Cyrus IMAP server indicates a systemic issue in how the codebase handles integer arithmetic operations, particularly in contexts involving network input processing.
Mitigation strategies for CVE-2015-8078 should focus on immediate patching of affected systems with the official security updates provided by Cyrus IMAP developers, as well as implementing network-level controls to restrict access to IMAP services where possible. Organizations should also consider implementing monitoring solutions that can detect anomalous URL fetch patterns or unusual memory access behaviors that might indicate exploitation attempts. The vulnerability's nature suggests that defensive measures should include input validation at multiple levels, including protocol-level checks and runtime bounds verification for all integer operations involving memory offsets or range calculations. System administrators should implement principle of least privilege for IMAP server processes, limiting the potential impact of successful exploitation through proper access controls and system hardening measures. Network segmentation and firewall rules can help reduce the attack surface by limiting access to IMAP services to trusted networks and IP addresses. Additionally, regular security audits of server codebases should include specific checks for integer overflow conditions, particularly in functions that handle network input or perform memory management operations. The vulnerability serves as a reminder of the importance of thorough vulnerability remediation and the need for comprehensive testing of security patches to ensure that all potential attack vectors have been addressed. Organizations should also consider implementing automated vulnerability scanning tools that can identify similar integer overflow conditions in other applications and systems within their infrastructure. The ATT&CK framework suggests that organizations should implement detection capabilities for exploitation attempts targeting remote services, particularly focusing on protocol-specific vulnerabilities that could allow for privilege escalation or data exfiltration. Regular updates to security configurations and continuous monitoring of system logs for unusual patterns in IMAP server operations can help identify potential exploitation attempts before they result in successful compromise of the email infrastructure.