CVE-2018-20786 in libvterm
Summary
by MITRE
libvterm through 0+bzr726, as used in Vim and other products, mishandles certain out-of-memory conditions, leading to a denial of service (application crash), related to screen.c, state.c, and vterm.c.
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Analysis
by VulDB Data Team • 08/25/2025
The vulnerability identified as CVE-2018-20786 affects libvterm versions up to 0+bzr726, a terminal emulation library widely utilized by applications including the popular Vim text editor. This flaw represents a critical denial of service vulnerability that stems from improper handling of out-of-memory conditions within the library's core components. The affected files screen.c, state.c, and vterm.c contain the specific implementation issues that allow malicious input to trigger application crashes. The vulnerability demonstrates a classic memory management error where the library fails to properly recover from memory allocation failures during terminal processing operations.
The technical nature of this vulnerability places it squarely within CWE-401, which addresses improper handling of memory allocation failures, and aligns with ATT&CK technique T1499.100 for Denial of Service through resource exhaustion. When libvterm encounters memory allocation failures during normal terminal processing, particularly while handling escape sequences or terminal state management, the library does not implement proper error recovery mechanisms. This results in the application crashing rather than gracefully handling the memory shortage condition. The vulnerability is particularly dangerous because it can be triggered through normal terminal input processing, making it exploitable via crafted terminal sequences that cause the library to attempt allocations that exceed available memory.
From an operational perspective, this vulnerability presents significant risk to systems relying on Vim or other applications using libvterm for terminal emulation. An attacker could potentially cause service disruption by sending specially crafted input sequences that trigger memory allocation failures, leading to application crashes and system unavailability. The impact extends beyond individual applications to affect entire terminal environments, as the vulnerability exists at the library level rather than being confined to specific applications. This makes it particularly concerning for server environments, automated systems, and any infrastructure where terminal emulation is critical for operations.
Mitigation strategies for CVE-2018-20786 should prioritize updating libvterm to versions that address the memory handling issues in the affected source files. System administrators should ensure that all applications using libvterm, particularly Vim and similar terminal emulators, are updated to versions containing the patched memory allocation handling code. Additionally, implementing proper input validation and sanitization at the application level can help reduce exposure by limiting the impact of potentially malicious terminal sequences. Monitoring and logging of terminal processing activities can aid in detecting exploitation attempts, while implementing resource limits and memory allocation safeguards can help prevent complete system crashes. Organizations should also consider implementing application sandboxing techniques to limit the impact of potential exploitation attempts. The vulnerability underscores the importance of robust error handling in memory-constrained environments and highlights the need for comprehensive testing of memory allocation failure scenarios in terminal processing libraries.