CVE-1999-0794 in Excel
Summary
by MITRE
Microsoft Excel does not warn a user when a macro is present in a Symbolic Link (SYLK) format file.
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Analysis
by VulDB Data Team • 04/19/2026
This vulnerability exists in Microsoft Excel versions prior to 97 SR2 and 2000 SR1 where the application fails to provide user warnings when executing macros contained within Symbolic Link format files. The SYLK format is a legacy data exchange format that was widely used for transferring data between different spreadsheet applications. When Excel opens a SYLK file, it processes the file content without proper validation of macro execution permissions, creating an environment where malicious code can be silently executed without user awareness. The vulnerability stems from the application's insufficient input validation and lack of macro security warnings during file processing. According to CWE-494, this represents a dangerous dependency on untrusted data processing where the application accepts and executes potentially malicious code without proper user consent. The flaw allows for privilege escalation attacks where attackers can embed malicious macros within seemingly legitimate SYLK files, exploiting the trust users place in spreadsheet applications.
The technical implementation of this vulnerability involves the parsing of SYLK file structures where macro commands are embedded within the data format itself. When Excel encounters a SYLK file containing macro instructions, it processes these commands without prompting the user for confirmation or displaying appropriate security warnings. This behavior creates a significant attack surface where social engineering can be combined with file format exploitation to deliver malicious payloads. The vulnerability is particularly dangerous because SYLK files were commonly used for data exchange between different applications, making them a trusted format that users would not typically scrutinize for security risks. Attackers could craft malicious SYLK files that appear legitimate but contain embedded macros that execute upon opening, potentially leading to complete system compromise.
The operational impact of this vulnerability extends beyond simple macro execution, as it enables sophisticated attack patterns that can bypass traditional security controls. Users operating under the assumption that Excel will warn them about potentially dangerous macro content are misled by the application's failure to provide these warnings. This creates a false sense of security that attackers can exploit to deliver malware, steal sensitive information, or establish persistent access to compromised systems. The vulnerability is particularly concerning in enterprise environments where users frequently exchange data files using legacy formats like SYLK. According to ATT&CK framework technique T1059.005, this vulnerability enables adversary access through macro execution, while T1566 covers the initial access vectors through malicious file attachments. The lack of user warnings makes this vulnerability especially dangerous for targeted attacks where attackers can craft convincing SYLK files that appear to be legitimate business documents.
Mitigation strategies for this vulnerability should focus on immediate application updates and user education. Microsoft released security patches for this vulnerability in service packs for Excel 97 and 2000, which introduced proper macro security warnings for SYLK files. Organizations should ensure all Excel installations are updated to the latest service packs and security updates. Additionally, users should be trained to recognize the risks associated with opening files from untrusted sources, particularly those containing macros. Security policies should enforce macro security settings that require explicit user consent before executing any macros, regardless of file format. Network-level controls can also be implemented to block or quarantine SYLK files from suspicious sources, while endpoint protection solutions should be configured to monitor for macro execution attempts. The vulnerability serves as a reminder of the importance of proper input validation and user warning mechanisms in software applications, particularly those handling data exchange formats that may contain executable content.