CVE-2000-0335 identifies a vulnerability in the GNU C Library (glibc) versions 2.0 through 2.1.3 and 8.2 through 8.2.2, specifically in the DNS resolver component. The resolver uses predictable transaction IDs when making DNS queries. DNS resolvers typically generate a random transaction ID to match responses with requests securely. However, in these affected versions, the predictability of these IDs allows a local attacker to spoof DNS query responses by guessing or predicting the transaction ID. This spoofing can lead to the attacker injecting malicious DNS responses, redirecting legitimate domain name resolutions to attacker-controlled IP addresses. The vulnerability affects confidentiality, integrity, and availability of network communications relying on DNS resolution. Exploitation does not require authentication but does require local access to the system to launch spoofed responses. The CVSS score of 7.5 (high severity) reflects the network attack vector, low attack complexity, no authentication required, and partial to complete impact on confidentiality, integrity, and availability. No patches are available for this vulnerability, and there are no known exploits in the wild, likely due to the age of the vulnerability and the requirement for local access. However, systems still running these legacy glibc versions remain at risk. Given the fundamental role of glibc in Linux-based systems, this vulnerability could be leveraged to redirect network traffic, perform man-in-the-middle attacks, or disrupt services relying on DNS resolution.

For European organizations, the impact of this vulnerability can be significant, especially for those running legacy Linux systems with affected glibc versions. DNS spoofing can lead to interception or redirection of sensitive communications, enabling data theft, credential compromise, or injection of malicious payloads. This undermines the confidentiality and integrity of internal and external communications. Critical infrastructure, financial institutions, and government agencies relying on vulnerable systems could face operational disruptions or data breaches. The availability of services may also be affected if DNS responses are manipulated to disrupt access to essential resources. Although exploitation requires local access, insider threats or compromised internal hosts could leverage this vulnerability to escalate attacks within organizational networks. The absence of patches means organizations must rely on alternative mitigations or system upgrades to reduce risk.

Since no patches are available for the affected glibc versions, European organizations should prioritize upgrading to modern, supported glibc versions where this vulnerability is resolved. For legacy systems that cannot be immediately upgraded, implement strict access controls to limit local user privileges and prevent unauthorized local access. Employ network segmentation to isolate vulnerable systems and monitor internal traffic for anomalous DNS activity. Use DNSSEC validation on resolvers to detect and reject spoofed DNS responses. Additionally, deploying host-based intrusion detection systems (HIDS) can help identify suspicious resolver behavior. Regularly audit systems to identify any running vulnerable glibc versions and plan for phased decommissioning or upgrade. Educate system administrators about the risks of legacy software and the importance of timely updates. Finally, consider using alternative DNS resolver implementations that do not exhibit this vulnerability if upgrading glibc is not feasible in the short term.