CVE-2015-8077 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 start_octet 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 CVE-2015-8077 represents a critical integer overflow flaw within the Cyrus IMAP server software that affects versions 2.3.19, 2.4.18, and 2.5.6. This vulnerability specifically resides in the index_urlfetch function located in the imap/index.c file, making it a core component of the email server's functionality that handles URL fetching operations. The issue stems from inadequate range validation and improper handling of the start_octet variable during urlfetch operations, creating a scenario where remote attackers can manipulate the system through carefully crafted requests. The vulnerability is particularly concerning because it represents an incomplete remediation of a previously identified flaw, CVE-2015-8076, indicating that the initial fix was insufficient to address all potential attack vectors. This pattern of partial remediation suggests a deeper architectural issue in how the software handles integer arithmetic and boundary conditions, particularly when processing user-supplied data that gets converted into internal processing parameters.
The technical exploitation of this vulnerability occurs when an attacker crafts malicious input that triggers an integer overflow in the start_octet variable during urlfetch range checks. When the integer overflow occurs, it can cause the system to misinterpret the intended range boundaries, potentially leading to memory corruption, buffer overflows, or other undefined behaviors that could be leveraged for remote code execution or denial of service attacks. The integer overflow specifically impacts the way the system calculates and validates the starting octet position in URL fetch operations, where the overflow can cause the calculated values to wrap around to extremely large or negative numbers. This type of vulnerability falls under CWE-190, Integer Overflow or Wraparound, which is classified as a fundamental weakness in software that can lead to serious security consequences when not properly addressed. The flaw demonstrates how seemingly minor arithmetic operations can become critical attack surfaces when proper input validation and boundary checking are omitted or inadequately implemented.
The operational impact of CVE-2015-8077 extends beyond simple denial of service scenarios, potentially enabling remote code execution or privilege escalation depending on the specific system configuration and attack vector employed. Since the Cyrus IMAP server is commonly deployed in enterprise environments and email infrastructure, successful exploitation could compromise email communications, access sensitive data, or provide attackers with persistent access to network resources. The vulnerability affects the core IMAP protocol implementation, making it particularly dangerous as it can be triggered through standard email operations that users perform regularly. Attackers could leverage this vulnerability to manipulate email processing workflows, potentially accessing confidential communications or disrupting email services entirely. The incomplete nature of the fix for CVE-2015-8076 indicates that the software maintainers may have overlooked edge cases or alternative attack paths that could still result in similar overflow conditions, suggesting a broader need for comprehensive security auditing of integer handling throughout the codebase.
Mitigation strategies for CVE-2015-8077 require immediate deployment of vendor patches that properly address the integer overflow conditions in the start_octet variable handling. Organizations should implement network-level restrictions to limit access to IMAP services from untrusted networks and consider disabling urlfetch functionality if it is not essential for business operations. The fix should include proper input validation that prevents integer overflow conditions by implementing bounds checking, using safe integer arithmetic operations, and ensuring that all range calculations account for potential overflow scenarios. Security monitoring should be enhanced to detect unusual urlfetch operations or patterns that might indicate exploitation attempts. Additionally, implementing proper code review processes that specifically focus on integer handling, buffer management, and boundary conditions can prevent similar vulnerabilities from being introduced in future releases. The ATT&CK framework categorizes this vulnerability under privilege escalation and remote code execution tactics, emphasizing the need for layered security approaches that include network segmentation, access controls, and continuous monitoring to protect against exploitation attempts. Organizations should also consider implementing intrusion detection systems that can identify patterns consistent with integer overflow exploitation attempts and ensure that all IMAP server instances are updated to versions that contain proper fixes for both CVE-2015-8076 and CVE-2015-8077.