CVE-2017-1000369 in Exim
Summary
by MITRE
Exim supports the use of multiple "-p" command line arguments which are malloc()'ed and never free()'ed, used in conjunction with other issues allows attackers to cause arbitrary code execution. This affects exim version 4.89 and earlier. Please note that at this time upstream has released a patch (commit 65e061b76867a9ea7aeeb535341b790b90ae6c21), but it is not known if a new point release is available that addresses this issue at this time.
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Analysis
by VulDB Data Team • 12/08/2022
The vulnerability identified as CVE-2017-1000369 represents a critical memory management flaw within the Exim email transfer agent that affects versions 4.89 and earlier. This issue stems from improper handling of command line arguments, specifically multiple "-p" flags that trigger memory allocation without subsequent deallocation. The flaw creates a memory leak condition where malloc() calls allocate memory blocks that remain unreleased through the program's execution lifecycle, ultimately leading to potential arbitrary code execution capabilities for attackers who can manipulate the command line parameters.
The technical implementation of this vulnerability involves the interaction between multiple command line arguments and the memory allocation system within Exim's processing logic. When multiple "-p" arguments are processed, each triggers a malloc() operation that allocates memory for processing parameters, but these allocated memory blocks are never properly freed through corresponding free() calls. This memory leak becomes exploitable when combined with other existing vulnerabilities within the system, creating conditions that allow attackers to manipulate memory layout and potentially execute malicious code with the privileges of the Exim process. The flaw aligns with CWE-401: Improper Release of Memory and CWE-122: Heap-based Buffer Overflow, representing both memory management issues that can lead to code execution.
The operational impact of this vulnerability extends beyond simple memory consumption issues, as it provides attackers with a pathway to achieve arbitrary code execution within the context of the Exim service. This represents a severe privilege escalation vector since Exim typically runs with elevated privileges to handle email processing tasks. Attackers can leverage this vulnerability to execute malicious payloads, potentially gaining unauthorized access to email servers, compromising email communications, or using the compromised system as a stepping stone for further network infiltration. The vulnerability's exploitation requires careful crafting of command line arguments but does not necessarily require authentication, making it particularly dangerous for systems where Exim is accessible to untrusted users or processes.
The remediation strategy for this vulnerability centers on applying the upstream patch referenced in commit 65e061b76867a9ea7aeeb535341b790b90ae6c21, which addresses the memory management issue by ensuring proper deallocation of malloc() allocated memory blocks. Organizations should prioritize updating their Exim installations to versions that include this fix, as the patch directly addresses the root cause of the memory leak. Additionally, system administrators should implement monitoring for unusual command line argument patterns that might indicate exploitation attempts, and consider implementing access controls to limit who can invoke Exim with potentially dangerous parameters. The vulnerability demonstrates the importance of proper memory management in security-critical applications and aligns with ATT&CK technique T1059.007: Command and Scripting Interpreter: PowerShell, as exploitation may involve crafting command line parameters to trigger the vulnerability. Organizations should also conduct regular security assessments of their email infrastructure to identify similar memory management issues that could present analogous risks.