CVE-2019-5598 in Solaris
Summary
by MITRE
In FreeBSD 11.3-PRERELEASE before r345378, 12.0-STABLE before r345377, 11.2-RELEASE before 11.2-RELEASE-p10, and 12.0-RELEASE before 12.0-RELEASE-p4, a bug in pf does not check if the outer ICMP or ICMP6 packet has the same destination IP as the source IP of the inner protocol packet allowing a maliciously crafted ICMP/ICMP6 packet could bypass the packet filter rules and be passed to a host that would otherwise be unavailable.
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Analysis
by VulDB Data Team • 04/03/2025
The vulnerability described in CVE-2019-5598 represents a critical flaw in FreeBSD's packet filtering system known as pf. This issue affects multiple versions of the FreeBSD operating system including specific prerelease and release versions of both FreeBSD 11.x and 12.x branches. The vulnerability specifically targets the handling of ICMP and ICMP6 packets within the pf firewall implementation, creating a potential security bypass mechanism that could allow unauthorized access to network resources. The flaw manifests when pf processes nested packet structures where outer ICMP/ICMP6 headers contain destination addresses that match the source addresses of inner protocol packets, effectively bypassing normal packet filtering rules.
The technical root cause of this vulnerability lies in the insufficient validation performed by pf when processing ICMP and ICMP6 packets that contain nested protocol information. According to CWE-284, this represents an improper access control issue where the system fails to properly validate packet headers before processing them. The flaw occurs during the packet inspection phase where pf does not verify that the outer packet's destination IP address matches the expected network topology before allowing the packet to traverse the filtering rules. This allows attackers to craft specially formatted ICMP/ICMP6 packets that appear to originate from legitimate sources while containing inner packets destined for restricted network segments. The vulnerability specifically impacts the packet filtering logic that should normally prevent packets from being forwarded to hosts that would otherwise be protected by firewall rules, creating a scenario where network isolation can be circumvented.
From an operational perspective, this vulnerability creates significant security implications for FreeBSD systems running affected versions. Attackers could potentially exploit this flaw to bypass network segmentation controls, gain access to internal network resources, or perform network reconnaissance activities that would normally be blocked by firewall rules. The impact extends beyond simple access bypass as it undermines the fundamental security model of packet filtering systems, potentially allowing for lateral movement within networks or direct access to protected services. This vulnerability particularly affects network infrastructure components that rely on pf for traffic control and security enforcement, including firewalls, routers, and network security appliances running FreeBSD. The issue also aligns with ATT&CK technique T1046 which involves network service scanning and reconnaissance, as attackers could use this bypass to map network topology and identify protected systems.
The mitigation strategy for CVE-2019-5598 involves upgrading affected FreeBSD systems to versions that contain the patched pf implementation. FreeBSD released updates addressing this vulnerability in the 11.2-RELEASE-p10 and 12.0-RELEASE-p4 releases, which included corrected packet validation logic for ICMP and ICMP6 packet processing. System administrators should also implement additional monitoring to detect anomalous packet patterns that might indicate exploitation attempts. Network administrators should review existing pf rules to ensure proper packet validation is enforced at multiple levels of the network stack, implementing redundant checks to prevent similar issues. The fix addresses the core validation issue by ensuring that outer ICMP/ICMP6 packet destination addresses are properly validated against expected network topology before allowing inner packet processing, thus preventing the bypass mechanism that enabled unauthorized packet forwarding. Organizations should also consider implementing network segmentation strategies that reduce the impact of such vulnerabilities and maintain regular patching schedules to address similar issues in network security infrastructure components.