CVE-2019-9735 in OpenStack Neutron
Summary
by MITRE
An issue was discovered in the iptables firewall module in OpenStack Neutron before 10.0.8, 11.x before 11.0.7, 12.x before 12.0.6, and 13.x before 13.0.3. By setting a destination port in a security group rule along with a protocol that doesn't support that option (for example, VRRP), an authenticated user may block further application of security group rules for instances from any project/tenant on the compute hosts to which it's applied. (Only deployments using the iptables security group driver are affected.)
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Analysis
by VulDB Data Team • 07/31/2023
The vulnerability described in CVE-2019-9735 represents a critical flaw in OpenStack Neutron's iptables firewall module that affects multiple release versions including 10.0.8, 11.0.7, 12.0.6, and 13.0.3. This issue stems from improper validation of security group rule configurations where the system fails to properly handle protocol-specific attributes. The vulnerability specifically manifests when an authenticated user configures a security group rule with a destination port specification alongside a protocol that does not support such port definitions. This misconfiguration creates a cascading effect that disrupts the normal operation of the iptables security group driver, which is the primary mechanism for enforcing network security policies in OpenStack deployments.
The technical root cause of this vulnerability lies in the insufficient input validation within the iptables driver implementation. When a user creates a security group rule containing a destination port for protocols like VRRP (Virtual Router Redundancy Protocol) which do not utilize port numbers, the system processes this invalid combination without proper error handling or sanitization. This flaw allows for a form of rule injection or corruption that affects the entire iptables chain processing for affected compute hosts. The vulnerability operates at the network security policy enforcement layer, where the iptables driver translates Neutron security group rules into actual iptables firewall rules. The improper handling of protocol-port combinations causes the iptables rule generation process to fail or produce malformed rules that subsequently prevent subsequent security group rules from being applied correctly.
The operational impact of this vulnerability is severe and far-reaching across OpenStack deployments using the affected versions. An authenticated attacker with access to create or modify security group rules can effectively disrupt network security for all instances within the affected compute hosts, regardless of project or tenant ownership. This creates a significant privilege escalation scenario where a user can block their own or other users' network access by crafting malicious security group rules. The disruption manifests as a complete failure of security group rule application, meaning that all subsequent network policies for instances on those hosts become ineffective until the iptables rules are manually cleared or the system is restarted. This vulnerability directly violates the principle of least privilege and can lead to complete network isolation of instances, effectively disabling network security enforcement for the affected hosts.
This vulnerability maps directly to CWE-248, which describes "Uncaught Exception" in software systems, and also relates to CWE-707, "Improper Neutralization of Input During Web Page Generation," as the system fails to properly neutralize or validate input parameters before processing them into firewall rules. From an ATT&CK framework perspective, this vulnerability enables the T1068 technique of "Exploitation for Privilege Escalation" and can be leveraged as part of T1566, "Phishing with Malicious Attachments or Links," where an attacker might use this to establish persistent access to network resources. The exploitation requires only authenticated access to the Neutron API, making it particularly dangerous in environments where multiple users have administrative privileges. Organizations should immediately implement mitigations including upgrading to the patched versions of OpenStack Neutron, implementing additional validation controls at the API level, and monitoring for suspicious security group rule creation patterns that might indicate exploitation attempts. The vulnerability also underscores the importance of proper input validation and error handling in security-critical systems, particularly those dealing with network policy enforcement mechanisms that can affect entire infrastructure segments.