CVE-2026-25749 in Vim
Summary
by MITRE • 02/07/2026
Vim is an open source, command line text editor. Prior to version 9.1.2132, a heap buffer overflow vulnerability exists in Vim's tag file resolution logic when processing the 'helpfile' option. The vulnerability is located in the get_tagfname() function in src/tag.c. When processing help file tags, Vim copies the user-controlled 'helpfile' option value into a fixed-size heap buffer of MAXPATHL + 1 bytes (typically 4097 bytes) using an unsafe STRCPY() operation without any bounds checking. This issue has been patched in version 9.1.2132.
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Analysis
by VulDB Data Team • 04/16/2026
The heap buffer overflow vulnerability identified as CVE-2026-25749 resides within Vim's tag file resolution mechanism, specifically affecting versions prior to 9.1.2132. This flaw manifests in the get_tagfname() function located in the src/tag.c source file, where the application processes user-controlled input through the 'helpfile' option. The vulnerability represents a classic buffer management issue that can be exploited to execute arbitrary code or cause application instability. The security implications are significant given Vim's widespread use across development environments, system administration tools, and various Unix-like operating systems where it serves as a default editor.
The technical exploitation occurs when Vim processes help file tags and copies user-supplied values from the 'helpfile' option into a fixed-size heap buffer. The buffer size is defined as MAXPATHL + 1 bytes, typically configured to 4097 bytes, but the implementation employs an unsafe STRCPY() operation without bounds verification. This primitive copy function does not validate the length of the source data against the destination buffer capacity, creating an opportunity for attackers to overflow the allocated memory space. The vulnerability classifies under CWE-121 Heap-based Buffer Overflow, which is categorized as a critical weakness in the CWE dictionary and maps directly to ATT&CK technique T1059.007 for command and scripting interpreter. The flaw demonstrates poor memory management practices where input validation and buffer boundary checking are completely omitted, creating a direct path for memory corruption.
The operational impact of this vulnerability extends beyond simple application crashes, as it provides potential attackers with opportunities to execute malicious code with the privileges of the user running Vim. Attackers could craft specially formatted helpfile option values that, when processed by the vulnerable get_tagfname() function, would overwrite adjacent memory locations and potentially redirect program execution flow. This makes the vulnerability particularly dangerous in environments where Vim is used with elevated privileges or in automated systems where users might be tricked into processing malicious help files. The exploitability is enhanced by the fact that the 'helpfile' option is a legitimate configuration parameter that users might interact with during normal Vim usage, making the attack surface more accessible than typical buffer overflow scenarios.
Mitigation strategies for CVE-2026-25749 require immediate patching of all affected Vim installations to version 9.1.2132 or later, which contains the necessary bounds checking fixes. System administrators should prioritize deployment of this security update across all environments where Vim is installed, particularly in production systems, development workstations, and any automated processes that might invoke Vim. Additional defensive measures include implementing strict input validation for user-supplied configuration options and monitoring for unusual helpfile option usage patterns. Organizations should also consider restricting write access to Vim configuration files and help directories to minimize potential attack vectors. The vulnerability demonstrates the importance of secure coding practices, specifically around buffer management and input validation, which aligns with security standards such as those outlined in the OWASP Top Ten and NIST SP 800-53 controls for secure software development lifecycle practices.