CVE-2005-2640 in Netscreen ScreenOS
Summary
by MITRE
Behavioral discrepancy information leak in Juniper Netscreen VPN running ScreenOS 5.2.0 and earlier, when using IKE with pre-shared key authentication, allows remote attackers to enumerate valid usernames via an IKE Aggressive Mode packet, which generates a response if the username is valid but does not respond when the username is invalid.
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Analysis
by VulDB Data Team • 06/30/2025
This vulnerability exists within Juniper Networks ScreenOS operating system versions 5.2.0 and earlier, specifically affecting VPN devices configured with IKE protocol using pre-shared key authentication methods. The flaw manifests as a behavioral discrepancy that occurs during the IKE Aggressive Mode authentication process, creating an information disclosure channel that enables remote attackers to perform username enumeration attacks. The vulnerability stems from the inconsistent response behavior of the system when processing IKE packets containing different username values.
The technical implementation of this vulnerability exploits the fundamental design flaw in how ScreenOS handles IKE Aggressive Mode negotiations. When an attacker sends an IKE Aggressive Mode packet with a username, the system responds differently based on whether the username exists in the configuration. Valid usernames trigger a specific response pattern that includes the transmission of an IKE notification message indicating authentication failure, while invalid usernames result in no response at all. This differential response behavior creates a timing-based information leak that can be exploited to distinguish between valid and invalid usernames through network traffic analysis.
The operational impact of this vulnerability extends beyond simple username enumeration, as it provides attackers with a foothold for further exploitation attempts. Once valid usernames are discovered, attackers can proceed with targeted password spraying attacks, credential stuffing operations, or proceed to more sophisticated exploitation techniques. The vulnerability affects the confidentiality aspect of the CIA triad by leaking authentication information that should remain private. According to CWE-200, this represents a weakness where information is disclosed to unauthorized actors, specifically through the exposure of authentication credentials through behavioral analysis.
Security professionals should note that this vulnerability aligns with ATT&CK technique T1111.001, which involves the use of sub-techniques for credential access through password spraying and brute force attacks. The information disclosure creates an automated attack vector that reduces the complexity of subsequent authentication attempts. Organizations with affected ScreenOS versions should immediately implement mitigation measures including upgrading to patched firmware versions, disabling IKE Aggressive Mode when possible, and implementing network segmentation to limit the attack surface. Additionally, monitoring network traffic for unusual IKE packet patterns can help detect exploitation attempts. The vulnerability demonstrates the critical importance of proper protocol implementation and the need for consistent error handling in security-sensitive systems, as inconsistent responses can inadvertently reveal system state information to unauthorized parties.