CVE-2017-6349 in VIM
Summary
by MITRE
An integer overflow at a u_read_undo memory allocation site would occur for vim before patch 8.0.0377, if it does not properly validate values for tree length when reading a corrupted undo file, which may lead to resultant buffer overflows.
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Analysis
by VulDB Data Team • 08/18/2020
The vulnerability identified as CVE-2017-6349 represents a critical integer overflow flaw within the vim text editor software that existed prior to version 8.0.0377. This issue manifests specifically within the u_read_undo function where memory allocation occurs during the processing of undo files. The vulnerability stems from inadequate validation of tree length values when vim encounters corrupted undo files, creating a scenario where maliciously crafted undo data could trigger unexpected behavior in the memory management system. The flaw operates at the intersection of memory safety and input validation, where the software fails to properly sanitize user-provided data before using it in arithmetic operations that determine memory allocation sizes.
The technical exploitation of this vulnerability occurs when vim attempts to read corrupted undo files that contain malformed tree length values. These invalid values, when processed through the integer arithmetic operations within the u_read_undo function, cause the calculated memory allocation size to exceed the bounds of the intended buffer or data structure. This overflow condition creates opportunities for subsequent buffer overflow scenarios where adjacent memory regions may be overwritten or corrupted. The vulnerability demonstrates characteristics consistent with CWE-190, Integer Overflow or Wraparound, which specifically addresses situations where integer arithmetic results in values that exceed the maximum representable value for the data type. The flaw essentially allows an attacker to manipulate the memory allocation process through crafted input data, potentially leading to arbitrary code execution or denial of service conditions.
From an operational perspective, this vulnerability presents significant security implications for systems relying on vim for text editing operations, particularly in environments where undo files might be processed from untrusted sources. The impact extends beyond simple application instability to potential privilege escalation scenarios, as the buffer overflow could be leveraged to execute malicious code within the context of the vim process. Attackers could craft malicious undo files that, when opened by vim, trigger the integer overflow condition and subsequently cause buffer overflows that may allow for memory corruption and arbitrary code execution. This vulnerability particularly affects systems where vim is used in automated processes or where undo files might be shared between different users or systems without proper validation. The ATT&CK framework categorizes this type of vulnerability under T1059 Command and Scripting Interpreter and T1203 Exploitation for Client Execution, as it represents a classic software exploitation vector targeting memory corruption vulnerabilities in widely used applications.
The mitigation strategies for CVE-2017-6349 primarily focus on applying the official patch version 8.0.0377 which addresses the integer overflow condition in the u_read_undo memory allocation site. System administrators should prioritize updating vim installations to versions that contain the fix, as this vulnerability has been classified as high severity by security organizations. Additional protective measures include implementing strict input validation for undo files, particularly when these files originate from untrusted sources, and configuring access controls to limit the ability to modify or create undo files in sensitive contexts. Organizations should also consider implementing application whitelisting policies that restrict the execution of vulnerable versions of vim, combined with regular security scanning to identify systems running outdated software versions. The patch specifically addresses the root cause by ensuring proper validation of tree length values before they are used in memory allocation calculations, thereby preventing the integer overflow condition that leads to subsequent buffer overflow scenarios.