CVE-2019-5597 in Solaris
Summary
by MITRE
In FreeBSD 11.3-PRERELEASE and 12.0-STABLE before r347591, 11.2-RELEASE before 11.2-RELEASE-p10, and 12.0-RELEASE before 12.0-RELEASE-p4, a bug in the pf IPv6 fragment reassembly logic incorrectly uses the last extension header offset from the last received packet instead of the first packet allowing maliciously crafted IPv6 packets to cause a crash or potentially bypass the packet filter.
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Analysis
by VulDB Data Team • 10/30/2023
The vulnerability described in CVE-2019-5597 affects FreeBSD operating systems versions 11.3-PRERELEASE and 12.0-STABLE prior to specific revision numbers, along with 11.2-RELEASE before p10 and 12.0-RELEASE before p4. This issue resides within the packet filter implementation known as pf, specifically targeting IPv6 fragment reassembly functionality. The flaw represents a critical security weakness that could potentially allow attackers to disrupt system operations or circumvent network security controls.
The technical implementation error occurs in the IPv6 fragment reassembly logic where the pf firewall component incorrectly processes extension headers during packet reconstruction. Rather than utilizing the offset value from the initial packet in the fragment sequence, the system retrieves and employs the offset from the final packet received. This misinterpretation of packet header information creates a scenario where malicious actors can craft specially designed IPv6 packets that exploit this logic flaw. The incorrect handling of extension header offsets during fragment reassembly leads to memory corruption conditions that can result in system crashes or unexpected behavior within the packet filtering mechanism.
The operational impact of this vulnerability extends beyond simple system instability as it potentially enables attackers to bypass network security controls implemented through the pf firewall. When the system crashes due to the malformed packet processing, network availability is compromised, creating a denial of service condition that could affect legitimate network traffic. More concerning is the potential for bypassing packet filtering rules, which could allow unauthorized access or traffic manipulation that undermines the security posture of the affected FreeBSD systems. The vulnerability affects systems where IPv6 packet filtering is actively utilized, making it particularly dangerous in environments where network security is paramount.
Mitigation strategies for CVE-2019-5597 should prioritize immediate system updates to the patched FreeBSD releases containing the corrected pf implementation. System administrators should ensure all affected FreeBSD installations are upgraded to versions 11.2-RELEASE-p10 or 12.0-RELEASE-p4, or to the appropriate revision numbers where the fix has been implemented. Network administrators should also consider implementing additional monitoring for unusual packet patterns that might indicate exploitation attempts. The fix addresses the core issue by correcting the extension header offset handling during IPv6 fragment reassembly, ensuring that the first packet's offset values are properly utilized rather than incorrectly relying on the final packet's data. This vulnerability aligns with CWE-129, representing an improper input validation issue, and could potentially be leveraged as part of ATT&CK technique T1071.004 for application layer protocol manipulation and T1499.004 for endpoint disruption through resource exhaustion or system instability.