CVE-1999-1053 in GuestBook
Summary
by MITRE
guestbook.pl cleanses user-inserted SSI commands by removing text between "<!--" and "-->" separators, which allows remote attackers to execute arbitrary commands when guestbook.pl is run on Apache 1.3.9 and possibly other versions, since Apache allows other closing sequences besides "-->".
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Analysis
by VulDB Data Team • 10/20/2025
This vulnerability exists in the guestbook.pl script which is commonly used to implement guestbooks on web servers. The script attempts to sanitize user input by removing text between <-- and -->, it fails to account for Apache's more permissive handling of comment termination sequences. This oversight creates a path for attackers to bypass the sanitization mechanism.
The technical flaw in guestbook.pl operates through a specific parsing weakness in how the script processes user input containing SSI commands. When users submit data containing SSI directives, the script removes content between standard comment delimiters, but Apache's SSI processor accepts alternative comment termination sequences beyond the standard "-->". Attackers can exploit this by crafting input that includes SSI commands with alternative comment endings that are not removed by the script's sanitization routine. This allows malicious commands to persist in the user input and be executed when the guestbook.pl script processes the data on the web server. The vulnerability specifically affects Apache 1.3.9 and potentially other versions where this alternative comment handling behavior exists.
The operational impact of this vulnerability is severe as it allows remote attackers to execute arbitrary commands on the affected web server with the privileges of the web server process. This creates a complete compromise of the server's security posture, enabling attackers to gain unauthorized access to system resources, modify or delete data, and potentially establish persistent access. The vulnerability affects any system running the vulnerable guestbook.pl script on Apache servers, making it a widespread concern for web administrators. Since the script typically runs with web server privileges, successful exploitation can lead to full system compromise, data theft, and potential lateral movement within the network infrastructure.
The vulnerability can be classified under CWE-94, which describes "Improper Control of Generation of Code ('Code Injection')", and specifically relates to CWE-1078, "Improper Neutralization of Special Elements used in a Command". From an ATT&CK perspective, this maps to T1059.007 for "Command and Scripting Interpreter: Unix Shell" and T1068 for "Exploitation for Privilege Escalation". Organizations should implement immediate mitigations including patching the vulnerable script to properly handle all comment termination sequences, disabling SSI functionality in guestbook scripts, or implementing proper input validation and sanitization that accounts for all possible comment syntax variations. Additionally, web server configurations should be reviewed to ensure proper SSI restrictions are in place, and input validation should be implemented at multiple layers to prevent such injection attacks from succeeding.