CVE-1999-0727 in OpenBSD
Summary
by MITRE
A kernel leak in the OpenBSD kernel allows IPsec packets to be sent unencrypted.
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Analysis
by VulDB Data Team • 04/19/2026
The vulnerability described in CVE-1999-0727 represents a critical security flaw within the OpenBSD operating system kernel that fundamentally undermines the integrity of the IPsec security framework. This issue specifically affects the kernel's handling of IPsec packet processing, creating a scenario where encrypted packets can be transmitted without proper encryption, thereby exposing sensitive network communications to potential interception and eavesdropping. The flaw exists at the kernel level, making it particularly dangerous as it operates below the application layer where typical security controls might be implemented. The vulnerability directly impacts the confidentiality aspect of the CIA triad by allowing unauthorized access to network traffic that should remain protected through IPsec encryption mechanisms.
The technical implementation of this kernel leak stems from a failure in the IPsec packet processing logic within the OpenBSD kernel codebase. When IPsec packets are processed through the kernel, the system should automatically encrypt traffic according to configured security policies and protocols such as IPSec ESP and AH. However, the vulnerability allows packets to bypass the encryption process entirely, resulting in plaintext transmission of data that should be protected. This represents a fundamental breakdown in the kernel's security enforcement mechanisms, where the system fails to properly validate or enforce the encryption requirements for IPsec traffic. The flaw demonstrates a classic case of improper input validation and security policy enforcement, which aligns with CWE-252, indicating a lack of proper security checks in the kernel's packet processing pipeline.
The operational impact of this vulnerability extends beyond simple data exposure, as it fundamentally compromises the trust model that IPsec is designed to establish between network entities. Network administrators who rely on IPsec for securing communications between remote sites, virtual private networks, or secure remote access connections face significant risk when this vulnerability exists. The unencrypted transmission of packets means that sensitive information including authentication credentials, business data, and confidential communications can be intercepted and read by malicious actors on the network. This vulnerability particularly affects environments where IPsec is used for site-to-site connections or remote access solutions, where the expectation is that all traffic between endpoints remains protected. The flaw essentially creates a backdoor in the network security architecture that undermines the entire purpose of implementing IPsec encryption protocols.
Mitigation strategies for CVE-1999-0727 require immediate system updates and patches from OpenBSD maintainers, as the vulnerability exists at the core kernel level where manual workarounds are not feasible. Organizations should implement network monitoring solutions to detect anomalous traffic patterns that might indicate unencrypted packet transmission, though this represents a reactive approach rather than a preventive solution. The recommended approach involves upgrading to patched versions of OpenBSD where the kernel-level flaw has been addressed through proper input validation and security policy enforcement mechanisms. Security teams should also consider implementing additional network segmentation and access controls to limit the potential impact of such vulnerabilities, while ensuring that all IPsec configurations are properly tested and validated. This vulnerability highlights the critical importance of kernel security and the need for comprehensive testing of security features at the lowest levels of the operating system, aligning with ATT&CK technique T1543.003 for kernel-level modifications and privilege escalation vectors that could be exploited to compromise system security.