CVE-2015-7755 in ScreenOS
Summary
by MITRE
Juniper ScreenOS 6.2.0r15 through 6.2.0r18, 6.3.0r12 before 6.3.0r12b, 6.3.0r13 before 6.3.0r13b, 6.3.0r14 before 6.3.0r14b, 6.3.0r15 before 6.3.0r15b, 6.3.0r16 before 6.3.0r16b, 6.3.0r17 before 6.3.0r17b, 6.3.0r18 before 6.3.0r18b, 6.3.0r19 before 6.3.0r19b, and 6.3.0r20 before 6.3.0r21 allows remote attackers to obtain administrative access by entering an unspecified password during a (1) SSH or (2) TELNET session.
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Analysis
by VulDB Data Team • 04/23/2026
The vulnerability identified as CVE-2015-7755 represents a critical authentication flaw in Juniper ScreenOS firewall software that affects multiple versions within the 6.2.0 and 6.3.0 release series. This weakness specifically impacts the authentication mechanism during remote management sessions, creating a pathway for unauthorized administrative access that could compromise entire network infrastructures. The vulnerability manifests when users attempt to establish SSH or TELNET connections to affected devices, where an unspecified password condition allows attackers to bypass normal authentication procedures and gain full administrative privileges.
Technical analysis reveals this flaw operates at the authentication protocol level, where the ScreenOS software fails to properly validate user credentials during the initial connection handshake process. The vulnerability's impact is particularly severe because it affects both secure shell and telnet protocols, which are commonly used for remote administrative access to network devices. This authentication bypass enables attackers to assume complete control over affected firewalls without proper authorization, potentially allowing them to modify firewall rules, access sensitive network traffic, or establish persistent backdoor access points. The flaw essentially creates a backdoor authentication mechanism that circumvents standard security controls.
The operational impact of CVE-2015-7755 extends far beyond individual device compromise, as firewalls serve as critical network security boundaries. When exploited, this vulnerability allows attackers to gain administrative access to network perimeters, potentially enabling lateral movement throughout the network infrastructure. Organizations with multiple affected devices face significant risk, as a single successful exploitation can provide access to entire network segments. The vulnerability's presence in multiple release versions within the 6.2.0 and 6.3.0 series suggests a systemic issue in the authentication implementation that was not properly addressed through the affected release cycles. Network security monitoring systems may not detect this attack vector as it appears to be a legitimate authentication process, making detection particularly challenging.
Mitigation strategies for CVE-2015-7755 require immediate patching of all affected ScreenOS versions to the latest secure releases. Organizations should implement comprehensive network segmentation and access controls to limit exposure, while also conducting thorough vulnerability assessments to identify any potential exploitation attempts. Network administrators must disable unnecessary telnet access and enforce the use of secure SSH protocols exclusively. Security monitoring should be enhanced to detect anomalous authentication patterns and unauthorized administrative access attempts. The vulnerability aligns with CWE-287 which addresses improper authentication issues, and maps to ATT&CK technique T1078 for valid accounts and privilege escalation. Organizations should also consider implementing network access control lists and regular security audits to prevent unauthorized access to network management interfaces, while maintaining detailed logging of all administrative activities for forensic analysis purposes.