CVE-1999-1417 describes a format string vulnerability in the AnswerBook2 (AB2) web server dwhttpd version 3.1a4. This vulnerability arises from improper handling of encoded percent (%) characters within HTTP requests. Specifically, the web server incorrectly logs these encoded characters, leading to a format string flaw. Format string vulnerabilities occur when user-supplied input is unsafely used as a format string parameter in functions like printf, allowing attackers to manipulate the format specifiers. In this case, remote attackers can craft malicious HTTP requests containing encoded % characters that exploit this flaw. The consequences include causing a denial of service (DoS) by crashing the server or potentially executing arbitrary commands remotely. The vulnerability is remotely exploitable without authentication or user interaction, making it particularly dangerous. The CVSS v2 score is 7.5 (high severity) with vector AV:N/AC:L/Au:N/C:P/I:P/A:P, indicating network attack vector, low attack complexity, no authentication required, and partial impact on confidentiality, integrity, and availability. No patches are available, and no known exploits have been reported in the wild, likely due to the age of the software and vulnerability (published in 1998). However, the underlying issue remains a critical security risk if the vulnerable software is still in use. The AnswerBook2 web server dwhttpd is an older product, historically used in some UNIX environments for serving documentation and web content. The vulnerability highlights the risks of legacy software with unpatched critical flaws, especially format string vulnerabilities that can lead to remote code execution.

For European organizations, the impact of this vulnerability depends largely on whether they still operate legacy systems running AnswerBook2 dwhttpd 3.1a4 or similar vulnerable versions. If such systems are exposed to the internet or accessible within internal networks, attackers could remotely exploit this flaw to cause denial of service, disrupting critical services or internal documentation portals. More severely, the possibility of arbitrary command execution could allow attackers to gain unauthorized access, escalate privileges, or move laterally within the network, potentially compromising sensitive data and system integrity. Given the vulnerability requires no authentication and can be triggered remotely, it poses a significant risk to confidentiality, integrity, and availability. Although the software is outdated, some industrial, governmental, or research institutions in Europe might still rely on legacy UNIX systems for specialized applications, making them vulnerable. The lack of patches means organizations must rely on compensating controls. The threat could also be leveraged in targeted attacks against organizations with legacy infrastructure, especially those in sectors with less frequent system upgrades, such as manufacturing, energy, or academia.

Since no official patches are available for this vulnerability, European organizations should take the following specific actions: 1) Identify and inventory all systems running AnswerBook2 dwhttpd 3.1a4 or related vulnerable versions. 2) Immediately isolate or decommission these legacy web servers from internet-facing roles or critical internal networks to reduce exposure. 3) Employ network-level controls such as firewall rules or intrusion prevention systems (IPS) to block or monitor suspicious HTTP requests containing encoded percent characters or unusual format string patterns targeting these servers. 4) Consider deploying web application firewalls (WAFs) with custom rules to detect and block exploitation attempts. 5) If legacy systems must remain operational, run them in isolated network segments with strict access controls and continuous monitoring for anomalous activities. 6) Plan and execute migration strategies to replace AnswerBook2 dwhttpd with modern, supported web server software that receives security updates. 7) Conduct regular security assessments and penetration tests focusing on legacy infrastructure to identify and remediate similar vulnerabilities. 8) Educate system administrators about the risks of legacy software and the importance of timely upgrades and network segmentation.