CVE-2019-20079 in VIM
Summary
by MITRE
The autocmd feature in window.c in Vim before 8.1.2136 accesses freed memory.
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Analysis
by VulDB Data Team • 03/18/2024
The vulnerability identified as CVE-2019-20079 resides within the autocmd functionality of Vim text editor, specifically in the window.c source file. This issue affects versions prior to 8.1.2136 and represents a classic use-after-free memory corruption flaw that can potentially be exploited by malicious actors. The vulnerability manifests when Vim processes autocmd events in window management contexts, creating conditions where memory previously allocated to window structures becomes accessible after being freed, leading to unpredictable behavior and potential code execution.
The technical flaw occurs within the autocmd processing mechanism where Vim maintains references to window structures that may be destroyed during autocmd execution. When an autocmd event triggers window manipulation operations, the system attempts to access memory that has already been deallocated, creating a use-after-free condition. This type of vulnerability falls under CWE-416 which specifically addresses the use of freed memory, and can be categorized under the broader ATT&CK technique T1059.007 for command and scripting interpreter. The memory access pattern typically involves a sequence where a window structure is freed during autocmd processing, but subsequent operations attempt to reference that freed memory location.
The operational impact of this vulnerability extends beyond simple memory corruption, as it can enable remote code execution when a malicious actor crafts specific input that triggers the vulnerable autocmd sequence. Attackers could potentially exploit this by creating crafted vimrc files or documents that when opened by an unpatched Vim version would trigger the use-after-free condition. The vulnerability is particularly concerning in environments where users frequently open untrusted documents or where Vim is used in automated processing pipelines. The exploitation typically requires the victim to open a malicious file or document that contains specific autocmd triggers, making social engineering a potential attack vector. This vulnerability affects all versions of Vim prior to 8.1.2136 and represents a critical security risk for systems where Vim is used for document editing and processing.
Mitigation strategies for CVE-2019-20079 primarily focus on immediate patching of affected Vim installations to version 8.1.2136 or later, which contains the necessary memory management fixes. System administrators should prioritize updating Vim across all affected systems, particularly those handling untrusted content or operating in multi-user environments. Additional protective measures include implementing strict file access controls and limiting the execution of autocmds in untrusted contexts. Organizations should also consider deploying security monitoring solutions that can detect anomalous memory access patterns or potential exploitation attempts. The fix implemented in the patched version addresses the core memory management issue by ensuring proper reference counting and memory lifecycle management during autocmd processing, preventing the access to freed memory structures that previously led to the vulnerability.