CVE-2000-0898 in Small HTTP Server
Summary
by MITRE
Small HTTP Server 2.01 does not properly process Server Side Includes (SSI) tags that contain null values, which allows local users, and possibly remote attackers, to cause the server to crash by inserting the SSI into an HTML file.
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Analysis
by VulDB Data Team • 04/06/2019
The vulnerability identified as CVE-2000-0898 affects Small HTTP Server version 2.01 and represents a classic buffer over-read condition within the Server Side Includes processing mechanism. This flaw exists in how the server handles SSI tags containing null byte sequences, creating a potential denial of service scenario that could be exploited by both local and remote threat actors. The issue stems from insufficient input validation and sanitization within the server's SSI parser implementation, where null values are not properly handled during the processing of embedded include directives.
The technical exploitation of this vulnerability occurs when an attacker crafts an HTML file containing SSI tags with embedded null characters, which the server then attempts to process without adequate boundary checking. When the server encounters these malformed SSI directives, it fails to properly terminate string processing or validate the presence of null bytes within the tag structure. This improper handling leads to memory access violations and subsequent server crashes, effectively rendering the web service unavailable to legitimate users. The vulnerability specifically targets the server's ability to parse and execute SSI commands, making it particularly dangerous in environments where dynamic content generation is relied upon.
From an operational impact perspective, this vulnerability creates significant risk for web servers running the affected Small HTTP Server software, as it can be leveraged to cause persistent service disruption. The potential for remote exploitation means that attackers outside the local network can trigger the crash without requiring authentication or physical access to the system. This makes the vulnerability particularly attractive to malicious actors seeking to perform denial of service attacks against web services. The crash condition affects the server's stability and reliability, potentially leading to extended downtime and service unavailability that impacts business operations and user access to web content.
Security practitioners should implement immediate mitigations including updating to patched versions of the Small HTTP Server software, implementing input validation measures for SSI tag processing, and configuring network-level restrictions to limit exposure to potentially malicious SSI content. The vulnerability aligns with CWE-125, which addresses out-of-bounds read conditions, and represents a classic example of improper input validation that can lead to system instability. From an attack framework perspective, this vulnerability could be categorized under ATT&CK technique T1499.004 for network denial of service, and may also align with T1059.007 for command and scripting interpreter usage in crafting malicious SSI content. Organizations should also consider implementing web application firewalls to detect and block suspicious SSI tag patterns and establish monitoring procedures to identify potential exploitation attempts. The vulnerability demonstrates the critical importance of proper input sanitization and boundary checking in web server implementations, particularly when processing dynamic content directives that require extensive parsing logic.