Heap Buffer Overflow in Vim Text Editor

Executive Summary

CVE-2026-52859 is an out-of-bounds read vulnerability in the Vim text editor versions prior to 9.2.0565. It occurs in the update_snapshot() function in src/terminal.c, which copies the visible terminal screen into the scrollback buffer. The function processes each screen cell's character array without checking an upper bound, stopping only at a NUL terminator. However, when a cell contains the maximum allowed six characters (a base character plus five combining marks), the bundled libvterm returns the array without a terminating NUL. This causes the function to read beyond the fixed six-element array, appending out-of-bounds values to a buffer reserved for only six characters.

An attacker can exploit this by sending a specific short byte sequence to a terminal window in Vim, which triggers the out-of-bounds read and leads to a crash of the Vim editor.

The vulnerability was fixed in Vim version 9.2.0565 by adding a loop bound check to ensure the character processing does not exceed the maximum allowed characters per cell.

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Impact Analysis

This vulnerability can cause the Vim editor to crash when processing certain terminal output containing a specific byte sequence. This results in a denial of service (DoS) condition, where the user loses access to the Vim editor until it is restarted.

Since the issue is triggered by output rendered inside a :terminal window, an attacker who can control terminal output could exploit this to disrupt a user's workflow or automated processes relying on Vim.

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Detection Guidance

This vulnerability is triggered by a specific byte sequence sent to a Vim terminal window that causes an out-of-bounds read and crash. Detection involves identifying if Vim versions prior to 9.2.0565 are running and if any terminal output could trigger this issue.

Since the vulnerability causes a crash in Vim when processing terminal output, monitoring for unexpected Vim crashes or core dumps related to terminal usage can be an indicator.

There are no specific commands provided in the resources to detect the vulnerability directly on the network or system.

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Mitigation Strategies

The primary mitigation step is to update Vim to version 9.2.0565 or later, where the vulnerability has been fixed by adding proper bounds checking in the update_snapshot() function.

Until the update can be applied, avoid running untrusted programs or processing untrusted terminal output inside Vim terminal windows, as the vulnerability can be triggered by a crafted byte sequence.

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Compliance Impact

The provided information does not specify any direct impact of this vulnerability on compliance with common standards and regulations such as GDPR or HIPAA.

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