CVE-2025-0650 Overview
A security flaw has been discovered in Open Virtual Network (OVN) that allows specially crafted UDP packets to bypass egress access control lists (ACLs). This vulnerability affects OVN installations configured with a logical switch that has DNS records set on it and egress ACLs configured on the same switch. Successful exploitation can lead to unauthorized access to virtual machines and containers running on the OVN network.
Critical Impact
This vulnerability enables attackers to bypass network security controls through crafted UDP packets, potentially gaining unauthorized access to virtualized infrastructure and container environments.
Affected Products
- Open Virtual Network (OVN) with logical switches configured with DNS records
- OVN installations with egress ACLs on DNS-enabled logical switches
- Red Hat products using OVN (see Red Hat Security Advisories RHSA-2025:1083 through RHSA-2025:1097)
Discovery Timeline
- January 22, 2025 - Vulnerability disclosed on OpenWall OSS-Security mailing list
- January 23, 2025 - CVE-2025-0650 published to NVD
- February 6, 2025 - Last updated in NVD database
Technical Details for CVE-2025-0650
Vulnerability Analysis
This vulnerability (CWE-284: Improper Access Control) stems from a flaw in how OVN processes UDP packets in specific network configurations. When a logical switch is configured with both DNS records and egress ACLs, the packet processing logic fails to properly enforce access control rules for specially crafted UDP traffic.
The attack requires network access and exploits a race condition or logic flaw in the ACL evaluation path. While the attack complexity is considered high due to the specific configuration requirements, the potential impact is severe—allowing complete bypass of network segmentation controls that organizations rely on to isolate workloads.
Root Cause
The vulnerability originates from improper access control validation in OVN's packet processing pipeline. When DNS records are configured on a logical switch, the ACL evaluation logic for egress traffic does not properly handle certain UDP packet structures, allowing them to bypass the configured security rules.
Attack Vector
An attacker with network access to the OVN environment can craft malicious UDP packets designed to exploit the ACL bypass condition. The attack requires:
- Target OVN deployment with DNS records configured on a logical switch
- Egress ACLs configured on the same logical switch
- Ability to send UDP packets to the affected network segment
Once the crafted packets bypass the ACLs, attackers can establish unauthorized connections to virtual machines and containers that should be protected by egress filtering rules.
The vulnerability mechanism involves the packet classification logic failing to properly apply ACL rules when processing UDP traffic in the presence of DNS configurations. Technical details and patch information are available in the Red Hat CVE-2025-0650 Details and Red Hat Bug Report #2339537.
Detection Methods for CVE-2025-0650
Indicators of Compromise
- Unexpected UDP traffic originating from protected network segments that should be blocked by egress ACLs
- Anomalous DNS-related UDP packets with unusual sizes or malformed structures
- Connections to external destinations from VMs/containers that egress rules should prevent
- Audit log entries showing successful connections that contradict configured ACL policies
Detection Strategies
- Monitor OVN flow tables for unexpected packet flows that bypass configured ACL rules
- Implement network traffic analysis to detect UDP packets with characteristics associated with ACL bypass attempts
- Review OVN controller logs for anomalies in packet processing when DNS and ACLs are configured together
- Deploy intrusion detection signatures targeting crafted UDP packets attempting ACL evasion
Monitoring Recommendations
- Enable detailed logging on OVN logical switches with DNS and ACL configurations
- Implement traffic mirroring to capture and analyze UDP flows for forensic analysis
- Set up alerts for unauthorized outbound connections from protected workloads
- Regularly audit ACL effectiveness by testing egress rules with known-blocked destinations
How to Mitigate CVE-2025-0650
Immediate Actions Required
- Apply patches from Red Hat Security Advisories (RHSA-2025:1083 through RHSA-2025:1097) immediately
- Review OVN configurations to identify logical switches with both DNS records and egress ACLs
- Consider temporarily removing DNS records from logical switches with critical egress ACLs as an interim measure
- Implement additional network-level filtering outside of OVN for critical security boundaries
Patch Information
Red Hat has released multiple security advisories addressing this vulnerability. Organizations should apply the appropriate patches based on their deployed products:
- Red Hat Security Advisory RHSA-2025:1083
- Red Hat Security Advisory RHSA-2025:1084
- Red Hat Security Advisory RHSA-2025:1085
- Red Hat Security Advisory RHSA-2025:1086
- Red Hat Security Advisory RHSA-2025:1087
Additional advisories (RHSA-2025:1088 through RHSA-2025:1097) are available for various affected configurations.
Workarounds
- Separate DNS functionality from logical switches that require egress ACLs by using dedicated DNS infrastructure
- Implement compensating controls using external firewalls or security groups to enforce egress filtering
- If DNS on logical switches is not required, remove DNS records to eliminate the vulnerable configuration
- Deploy network microsegmentation using additional security layers independent of OVN ACLs
# Example: Check OVN logical switch configuration for vulnerable setup
# List logical switches with DNS records
ovn-nbctl list DNS
# List ACLs on logical switches
ovn-nbctl acl-list <logical_switch_name>
# If both DNS and egress ACLs exist on the same switch, apply patches or workarounds
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
