CVE-2016-1886 in FreeBSD
Summary
by MITRE
Integer signedness error in the genkbd_commonioctl function in sys/dev/kbd/kbd.c in FreeBSD 9.3 before p42, 10.1 before p34, 10.2 before p17, and 10.3 before p3 allows local users to obtain sensitive information from kernel memory, cause a denial of service (memory overwrite and kernel crash), or gain privileges via a negative value in the flen structure member in the arg argument in a SETFKEY ioctl call, which triggers a "two way heap and stack overflow."
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 07/06/2024
The vulnerability identified as CVE-2016-1886 represents a critical integer signedness error within the FreeBSD kernel's keyboard driver implementation. This flaw exists in the genkbd_commonioctl function located in sys/dev/kbd/kbd.c and affects multiple FreeBSD versions including 9.3 before patch level 42, 10.1 before patch level 34, 10.2 before patch level 17, and 10.3 before patch level 3. The vulnerability stems from improper handling of the flen structure member within the SETFKEY ioctl call, creating a dangerous condition where negative values can be processed without proper validation.
The technical exploitation of this vulnerability occurs through a specific sequence of operations involving the SETFKEY ioctl command. When a local user provides a negative value in the flen structure member, the kernel's processing logic fails to properly validate the signedness of this integer parameter. This oversight results in what security researchers term a "two way heap and stack overflow" condition, where both heap and stack memory regions become corrupted simultaneously. The flaw demonstrates characteristics consistent with CWE-190, Integer Overflow or Wraparound, and CWE-191, Integer Underflow, as the system fails to properly handle negative integer values in contexts where only positive values are expected.
The operational impact of this vulnerability is severe and multifaceted, encompassing information disclosure, denial of service, and privilege escalation capabilities. Attackers can leverage this flaw to extract sensitive information from kernel memory spaces, potentially accessing confidential data that should remain protected within the operating system's privileged execution environment. The memory overwrite conditions can also trigger kernel crashes, leading to system instability and denial of service scenarios that can affect critical infrastructure. Most concerning is the potential for privilege escalation, where local users could exploit the vulnerability to gain elevated system privileges, effectively compromising the entire system's security posture.
From a cybersecurity perspective, this vulnerability aligns with ATT&CK technique T1068, Exploitation for Privilege Escalation, and T1005, Data from Local System. The attack surface is particularly concerning because it operates at the kernel level, where successful exploitation can result in complete system compromise. The vulnerability's location within the keyboard driver module means that any local user with access to the system can potentially exploit it, making it especially dangerous in multi-user environments or systems where users may have varying privilege levels. The heap and stack overflow conditions create multiple attack vectors, allowing for both information leakage and system instability.
Mitigation strategies for CVE-2016-1886 should prioritize immediate patch application to the affected FreeBSD versions, ensuring that all systems receive the appropriate security updates that address the integer signedness error in the genkbd_commonioctl function. System administrators should also implement monitoring for unusual kernel memory access patterns and consider restricting local user privileges where possible to limit potential exploitation opportunities. Additional defensive measures include kernel memory protection mechanisms and regular security audits to identify similar vulnerabilities in other kernel modules. The vulnerability serves as a reminder of the critical importance of proper input validation and integer handling in kernel code, as even seemingly minor oversights can result in severe security consequences that affect the entire operating system's integrity and security model.