CVE-2026-6390 in nano
Summary
by MITRE • 07/23/2026
A flaw was found in GNU nano's multi-buffer error message handling. When a user opens multiple files at startup and one triggers an ALERT-level error, a specially crafted filename containing printf format specifiers can be reinterpreted. This format string vulnerability may allow an attacker to achieve stack information disclosure, cause a denial of service (crash), or potentially perform arbitrary memory writes.
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Analysis
by VulDB Data Team • 07/23/2026
This vulnerability exists within the GNU nano text editor's multi-buffer error handling mechanism, specifically when processing multiple files opened at startup. The flaw manifests as a format string vulnerability that occurs during ALERT-level error processing, where the application fails to properly sanitize user-provided filenames before using them in printf-family functions. When an attacker crafts a malicious filename containing format specifiers such as %x, %s, or %p, these sequences can be interpreted by the error handling code, leading to unintended behavior and information disclosure.
The technical exploitation of this vulnerability stems from inadequate input validation within nano's internal error message generation routines. According to CWE-134, this represents a classic format string vulnerability where attacker-controlled data is passed directly to printf without proper sanitization or formatting. The vulnerability operates at the application layer and can be triggered through the command line interface when multiple files are opened simultaneously. When one file triggers an ALERT-level error, the malformed filename gets processed through the error handling code path, allowing attackers to manipulate stack contents and potentially read memory addresses.
The operational impact of this vulnerability spans multiple security domains including information disclosure, denial of service, and potential arbitrary code execution. Stack information disclosure occurs when format specifiers like %p or %x are used to read memory addresses from the program stack, potentially revealing heap layout or other sensitive information that could aid in more sophisticated attacks. The denial of service component manifests as application crashes or hangs when malformed format strings cause the error handling logic to behave unpredictably. In theory, with sufficient control over the format string and knowledge of memory layout, attackers might be able to perform arbitrary memory writes through carefully crafted sequences.
This vulnerability aligns with ATT&CK technique T1059.007 for command and script injection, as it enables remote code execution through improper input handling in a text editing application. The attack surface is limited to scenarios where users open multiple files with potentially malicious filenames, but the impact extends beyond simple information disclosure due to the potential for memory corruption. Security practitioners should note that this vulnerability exists in the application's error handling path rather than core functionality, making it particularly insidious as it only triggers under specific error conditions.
Mitigation strategies include immediate patching of nano installations to address the format string handling issue, implementing input validation for filenames passed through command line arguments, and applying defensive programming practices such as using printf format strings that explicitly specify argument positions. Organizations should also consider implementing file access controls and monitoring for unusual filename patterns in multi-file operations. The vulnerability demonstrates the importance of proper input sanitization even in error handling code paths, as these areas are often overlooked during security reviews and may contain critical flaws due to their specialized nature.