CVE-1999-0273 in Solaris
Summary
by MITRE
denial of service through solaris 2.5.1 telnet by sending ^d characters.
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Analysis
by VulDB Data Team • 04/17/2026
The vulnerability described in CVE-1999-0273 represents a classic denial of service flaw affecting Sun Solaris 2.5.1 systems through the telnet service. This issue stems from improper handling of specific control characters, particularly the ^d character sequence, which can be used to disrupt the normal operation of the telnet daemon. The vulnerability manifests when a remote attacker sends a sequence containing the ^d character to a telnet session, causing the service to terminate unexpectedly and rendering the system unavailable to legitimate users. This type of vulnerability falls under the category of improper input handling and demonstrates how seemingly benign control characters can be exploited to compromise system availability.
The technical root cause of this vulnerability lies in the telnet daemon's inadequate processing of terminal control sequences, specifically how it interprets and handles the ^d character which traditionally represents the end-of-file signal in unix-like systems. When the telnet service receives this character sequence, it fails to properly validate or sanitize the input before processing it, leading to an unexpected termination of the service. This behavior can be analyzed through the CWE-20 framework, which categorizes the issue as improper input validation, and more specifically aligns with CWE-129 which deals with insufficient validation of length of inputs. The vulnerability represents a failure in the input sanitization process that allows malicious control characters to disrupt service operations.
The operational impact of this vulnerability extends beyond simple service disruption, as it can be exploited by attackers to systematically deny access to critical system administration services. In enterprise environments where telnet remains in use for legacy system management, this vulnerability can provide attackers with a means to gain unauthorized access to system resources or simply render administrative services unavailable. The attack vector is particularly concerning because it requires minimal privileges and can be executed remotely, making it an attractive target for denial of service attacks. From an ATT&CK perspective, this vulnerability aligns with the T1499.004 technique for network denial of service, where attackers leverage weaknesses in network services to disrupt availability. The vulnerability also demonstrates the importance of proper signal handling in daemon processes and highlights how control character sequences can be weaponized in system exploitation.
Mitigation strategies for this vulnerability should focus on both immediate remediation and long-term architectural improvements. System administrators should apply the appropriate security patches provided by Sun Microsystems for Solaris 2.5.1, which typically include enhanced input validation for control characters in the telnet daemon. Additionally, organizations should consider implementing network-level filtering to prevent unauthorized access to telnet services or migrate to more secure alternatives such as SSH protocols. The vulnerability underscores the critical importance of input validation in network services and demonstrates why proper signal handling and character sequence validation should be integral components of security hardening procedures. Organizations should also implement monitoring solutions to detect unusual patterns of telnet traffic that might indicate exploitation attempts, particularly focusing on the detection of control character sequences that could trigger service termination.