CVE-2000-1010 in Linux
Summary
by MITRE
Format string vulnerability in talkd in OpenBSD and possibly other BSD-based OSes allows remote attackers to execute arbitrary commands via a user name that contains format characters.
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Analysis
by VulDB Data Team • 10/12/2025
The CVE-2000-1010 vulnerability represents a critical format string flaw in the talkd daemon that ships with OpenBSD and other BSD-based operating systems. This vulnerability exists within the network service that facilitates user-to-user messaging across Unix-like systems, making it a prime target for remote exploitation. The flaw specifically manifests when the talkd daemon processes user names containing format specifiers such as %s, %d, or %x without proper sanitization. These format characters can be manipulated by remote attackers to trigger undefined behavior in the application's printf-family function calls, potentially leading to memory corruption and arbitrary code execution.
The technical nature of this vulnerability aligns with CWE-134, which specifically addresses format string vulnerabilities where format strings are constructed from user-controlled data without proper validation or sanitization. This flaw operates at the application layer and leverages the inherent dangers of improper input handling in C-based network services. When an attacker crafts a malicious user name containing format specifiers, the talkd daemon processes this input through vulnerable printf calls, allowing the attacker to read arbitrary memory locations or overwrite critical program variables. The vulnerability is particularly dangerous because it can be exploited remotely without authentication, making it a significant threat to systems running the affected service.
The operational impact of CVE-2000-1010 extends beyond simple privilege escalation, as it provides attackers with full control over the compromised system. Attackers can leverage this vulnerability to execute arbitrary commands with the privileges of the talkd daemon process, which typically runs with elevated permissions. This can result in complete system compromise, data exfiltration, or the establishment of persistent backdoors. The vulnerability affects multiple BSD-based operating systems, including but not limited to OpenBSD, FreeBSD, and NetBSD, creating a widespread attack surface. Network-based attacks can be executed from any remote location, making this vulnerability particularly dangerous in environments where the talkd service is exposed to untrusted networks.
Security mitigations for CVE-2000-1010 should focus on immediate patching of affected systems and implementation of network segmentation policies. The primary fix involves updating the talkd daemon to properly sanitize user input before processing format strings, typically through the use of fixed format specifiers or explicit string validation. Organizations should disable the talkd service entirely if it is not required for operations, as this eliminates the attack surface entirely. Network administrators should implement firewall rules to block access to the talkd port 517 and 518, which are used by the service for communication. Additionally, monitoring for suspicious user name patterns containing format specifiers should be implemented as part of intrusion detection systems. This vulnerability demonstrates the importance of input validation and proper secure coding practices, as outlined in the software security principles of the MITRE ATT&CK framework under the technique of "Command and Scripting Interpreter" where format string vulnerabilities are categorized as a method of executing arbitrary code through malformed input.