CVE-2026-102727 in NetX Duo
Summary
by MITRE • 09/29/2026
FTP Passive Data Connection Not Bound to the Authenticated Control Peer
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Analysis
by VulDB Data Team • 09/29/2026
The vulnerability identified as FTP Passive Data Connection Not Bound to the Authenticated Control Peer represents a critical architectural flaw in how certain File Transfer Protocol implementations manage session state and connection binding. In standard FTP operations, two distinct TCP connections are established: a control connection for sending commands and receiving responses, and one or more data connections for transferring files. The passive mode of operation requires the server to open a random high-numbered port and instruct the client to connect back to it. This vulnerability arises when the server fails to strictly associate this newly opened data channel with the specific identity and authentication state of the control connection that initiated the request. Instead, the server may accept connections on the designated passive port from any source IP address or user session, effectively decoupling the data transfer mechanism from the security context established during the initial login process. This design oversight creates a significant gap in access control enforcement, allowing for potential unauthorized data exfiltration or injection attacks that bypass standard authentication checks at the application layer by exploiting the network-layer separation of channels.
From a technical perspective, this flaw is rooted in improper session management and lack of strict socket binding validation. When an authenticated user requests a file download via PASV command, the server allocates a port for incoming data connections but does not sufficiently verify that the subsequent connection attempt originates from the same IP address or matches the specific session token associated with the active control channel. In some implementations, this might manifest as accepting connections from any host on the network if the passive mode is configured to listen on all interfaces without binding to the client's source IP. This behavior contradicts the principle of least privilege and secure default configurations, where data channels should be ephemeral and tightly coupled to their controlling session. The absence of such validation allows an attacker who has gained access to a valid FTP account, or potentially even one with limited privileges, to manipulate the context in which data is transferred. Furthermore, if the implementation fails to validate that the source IP of the data connection matches the control connection's peer address, it opens the door for session hijacking scenarios where an internal network attacker could intercept or inject traffic into a legitimate user’s transfer by spoofing their IP address and connecting to the passive port before the legitimate client does.
The operational impact of this vulnerability is severe, particularly in environments handling sensitive data over unencrypted FTP protocols. An adversary can exploit this misconfiguration to perform unauthorized file uploads or downloads without needing full administrative privileges on the server, provided they have a valid low-privileged account. This facilitates data exfiltration where an attacker retrieves confidential files by initiating a passive transfer and then connecting from a different location if the binding is not enforced correctly, although typically it allows for more direct attacks such as directory traversal or file overwrite if combined with other flaws. Additionally, this vulnerability can be leveraged to conduct denial of service attacks against specific users by occupying their allocated data ports through rapid connection attempts from spoofed sources, thereby preventing legitimate transfers. In enterprise environments where FTP is used for automated batch processing between systems, this flaw could allow a compromised system on the same network segment to intercept or corrupt critical business files during transit, leading to significant integrity and confidentiality breaches that may violate regulatory compliance standards regarding data protection.
Mitigation strategies must focus on enforcing strict session binding and upgrading protocol usage where possible. The most effective remediation is to ensure that FTP server software explicitly binds passive mode data connections to the IP address of the authenticated control connection peer. Administrators should configure firewalls or intrusion prevention systems to validate that incoming passive port connections originate from the expected source IPs associated with active sessions. If the organization relies on legacy FTP infrastructure, implementing strict access controls and monitoring for anomalous connection patterns can help detect exploitation attempts in real-time. However, given the inherent insecurity of plaintext FTP protocols which lack encryption and robust integrity checks, the long-term solution is to migrate to secure alternatives such as SFTP (SSH File Transfer Protocol) or FTPS (FTP over SSL/TLS). These modern standards encapsulate both control and data channels within encrypted tunnels that are inherently bound to a single authenticated session, eliminating the possibility of channel separation attacks. Regular security audits and penetration testing should be conducted to verify that passive mode implementations correctly enforce these binding constraints across all supported versions of the affected software.
This vulnerability aligns with CWE-284 Improper Access Control, specifically regarding insufficient validation of user input or context in relation to session management. It also maps to MITRE ATT&CK technique T1071 Application Layer Protocol, as attackers may abuse standard FTP protocols to bypass security controls and establish covert channels for data exfiltration. The failure to bind the data connection to the authenticated peer is a classic example of how legacy protocol designs can introduce subtle but exploitable gaps in trust boundaries when not properly hardened against modern attack vectors that exploit network-level ambiguities.