CVE-2020-1763 in Libreswan
Summary
by MITRE
An out-of-bounds buffer read flaw was found in the pluto daemon of libreswan from versions 3.27 till 3.31 where, an unauthenticated attacker could use this flaw to crash libreswan by sending specially-crafted IKEv1 Informational Exchange packets. The daemon respawns after the crash.
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Analysis
by VulDB Data Team • 10/16/2020
The vulnerability CVE-2020-1763 represents a critical out-of-bounds buffer read flaw within the pluto daemon component of the libreswan IPsec implementation. This security issue affects versions 3.27 through 3.31 of the software, creating a significant risk for systems relying on IPsec-based secure communications. The pluto daemon serves as the primary IKE daemon responsible for managing Internet Key Exchange protocol operations, making it a critical component in establishing and maintaining secure network connections. The flaw specifically manifests during the processing of IKEv1 Informational Exchange packets, which are standard components of the IKE protocol used for exchanging non- IKE authentication messages between peers. This particular vulnerability falls under CWE-125, which describes out-of-bounds read conditions that can lead to unpredictable behavior and system instability.
The technical exploitation of this vulnerability occurs when an unauthenticated remote attacker sends specially crafted IKEv1 Informational Exchange packets to a vulnerable libreswan system. These malformed packets trigger a buffer read operation that exceeds the allocated memory boundaries, causing the pluto daemon to crash. The daemon's response to this crash is to automatically respawn, which means the system continues to operate but experiences temporary service disruption. The vulnerability stems from insufficient input validation and boundary checking within the packet processing logic of the pluto daemon. This flaw demonstrates poor defensive programming practices where the system fails to properly validate packet contents before attempting to process them, allowing malicious data to cause memory corruption. The impact is particularly concerning because the attack requires no authentication, making it accessible to anyone who can reach the target system's IPsec service port.
From an operational perspective, this vulnerability creates a denial-of-service risk that can disrupt secure communication channels established through IPsec. The automatic respawn mechanism provides some resilience but does not eliminate the service disruption that occurs during the crash and restart cycle. Network administrators may experience intermittent connectivity issues or temporary loss of secure tunnel functionality, potentially affecting business continuity and security posture. The vulnerability is particularly dangerous in environments where IPsec is used for critical infrastructure protection, remote access solutions, or secure inter-network communication. Organizations using affected libreswan versions may experience unexpected service interruptions that could be exploited by attackers to cause prolonged disruption or as part of a larger attack campaign. The attack vector's accessibility through unauthenticated network traffic means that any system exposed to the internet or internal networks could be vulnerable, creating widespread potential impact across various deployment scenarios.
The recommended mitigation strategy involves upgrading to libreswan version 3.32 or later, which contains the necessary patches to address the buffer read flaw. System administrators should prioritize this upgrade, especially in environments where IPsec services are critical to network operations. Additionally, implementing network-level protections such as firewall rules that restrict access to IPsec service ports can provide temporary defense while upgrades are being deployed. The vulnerability demonstrates the importance of proper input validation and memory safety practices in security-critical software components. Organizations should also consider implementing monitoring solutions to detect unusual patterns of daemon crashes or restarts that might indicate exploitation attempts. This vulnerability aligns with ATT&CK technique T1499.004, which covers network disruption attacks, and highlights the need for robust software security practices to prevent remote code execution and denial-of-service conditions in security infrastructure components.