CVE-2009-3936 in Online Plug-in
Summary
by MITRE
Unspecified vulnerability in Citrix Online Plug-in for Windows 11.0.x before 11.0.150 and 11.x before 11.2, Online Plug-in for Mac before 11.0, Receiver for iPhone before 1.0.3, and ICA Java, Mac, UNIX, and Windows Clients for XenApp and XenDesktop allows remote attackers to impersonate the SSL/TLS server and bypass authentication via a crafted certificate, a different vulnerability than CVE-2009-3555.
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Analysis
by VulDB Data Team • 11/29/2024
This vulnerability affects Citrix online and client software components including the Citrix Online Plug-in for Windows, Mac, and various XenApp and XenDesktop clients. The flaw resides in the SSL/TLS certificate validation mechanism where the software fails to properly verify server certificates, creating a security gap that allows man-in-the-middle attacks. Attackers can exploit this weakness by presenting a crafted certificate that appears legitimate to the vulnerable client software, enabling them to impersonate trusted servers without proper authentication. This represents a critical certificate validation failure that undermines the fundamental security assurances provided by SSL/TLS protocols.
The technical implementation of this vulnerability stems from insufficient certificate chain validation and trust verification processes within the Citrix client software. When the client establishes connections to Citrix servers, it should validate certificate authenticity through proper certificate chain verification, including checking certificate authorities, expiration dates, and domain name matching. However, the vulnerable versions fail to perform these critical validation steps, allowing attackers to present forged certificates that the client accepts as legitimate. This flaw operates at the transport layer security validation level and directly violates established security practices for SSL/TLS implementation. The vulnerability specifically impacts the certificate validation logic rather than other authentication mechanisms, making it distinct from similar issues like CVE-2009-3555 which affected different validation paths.
The operational impact of this vulnerability is severe as it allows remote attackers to conduct active man-in-the-middle attacks against Citrix connections. An attacker positioned between a client and server can intercept communications, modify data in transit, and potentially gain unauthorized access to sensitive information. The authentication bypass capability means that even if users believe they are connecting to legitimate Citrix servers, they may actually be communicating with attacker-controlled systems. This vulnerability affects multiple platforms including Windows, Mac, iOS, and UNIX systems, creating widespread exposure across enterprise environments that rely on Citrix virtual desktop and application delivery solutions. Organizations using these vulnerable versions face significant risk of data breaches, credential theft, and unauthorized system access.
Mitigation strategies should focus on immediate software updates to the patched versions of Citrix clients and online plug-ins. Organizations must ensure all affected systems are updated to versions 11.0.150 or later for Windows, 11.0 for Mac, 1.0.3 for iPhone, and appropriate versions for XenApp and XenDesktop clients. Network administrators should implement additional monitoring for suspicious certificate validation events and establish certificate pinning policies where possible. Security teams should also consider implementing network-based protections such as deep packet inspection to detect anomalous certificate behaviors. The vulnerability aligns with CWE-295 which addresses improper certificate validation, and represents a technique commonly used in ATT&CK framework under T1552 for credential access and T1046 for network service scanning. Organizations should also conduct thorough vulnerability assessments to identify any remaining systems that might be affected by similar certificate validation issues in other software components.