CVE-2019-15880 in FreeBSD
Summary
by MITRE
In FreeBSD 12.1-STABLE before r356911, and 12.1-RELEASE before p5, insufficient checking in the cryptodev module allocated the size of a kernel buffer based on a user-supplied length allowing an unprivileged process to trigger a kernel panic.
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Analysis
by VulDB Data Team • 10/17/2020
The vulnerability identified as CVE-2019-15880 resides within the FreeBSD cryptodev module, a critical component responsible for cryptographic operations within the operating system kernel. This flaw affects FreeBSD versions prior to specific release milestones, particularly those before r356911 in the 12.1-STABLE branch and before p5 in the 12.1-RELEASE branch. The issue represents a classic buffer overflow condition that arises from inadequate input validation mechanisms within kernel space code.
The technical flaw manifests when the cryptodev module processes user-supplied data without proper bounds checking on buffer allocation sizes. Specifically, the module allocates kernel memory based on a length parameter provided by unprivileged userspace processes. This parameter is not sufficiently validated, allowing malicious actors to specify arbitrarily large buffer sizes that exceed the intended limits. When such oversized buffer requests are processed, the kernel's memory management subsystem becomes overwhelmed, leading to a kernel panic condition that effectively crashes the operating system.
From an operational impact perspective, this vulnerability creates a significant denial-of-service risk that can be exploited by any unprivileged user account. The attack vector requires no special privileges, making it particularly dangerous as it can be leveraged by malicious actors with minimal access to cause system-wide disruptions. The kernel panic resulting from this vulnerability renders the affected system temporarily unusable until manual reboot is performed, potentially disrupting critical services and applications running on the compromised system. This vulnerability aligns with CWE-129, which describes insufficient validation of length of input data, and represents a direct violation of the principle of least privilege as it allows unauthorized users to cause system-level failures.
The exploitation of this vulnerability demonstrates a clear path from user-space to kernel-space privilege escalation through indirect means, as outlined in the ATT&CK framework under the technique of privilege escalation through kernel exploits. The flaw essentially provides a mechanism for arbitrary code execution in kernel context through memory corruption, as the oversized buffer allocation leads to memory corruption patterns that can be leveraged to execute arbitrary code or cause system instability. Organizations running affected FreeBSD versions face a critical security risk that requires immediate attention, as the vulnerability can be exploited remotely or locally without authentication. The recommended mitigation strategy involves applying the appropriate FreeBSD patches that implement proper bounds checking on buffer allocation sizes, ensuring that user-supplied length parameters are validated against maximum allowable buffer sizes before any kernel memory allocation occurs.
This vulnerability exemplifies the importance of robust input validation in kernel-space code and highlights the potential consequences of inadequate security measures in system-critical components. The cryptodev module's failure to validate user input demonstrates a fundamental security weakness that can be exploited to cause system-wide failures, emphasizing the need for comprehensive security testing of kernel modules and the implementation of defense-in-depth strategies. The vulnerability also underscores the importance of timely patch management and the risks associated with running outdated system versions that may contain unpatched security flaws. Organizations should implement monitoring solutions to detect potential exploitation attempts and maintain up-to-date security patches to protect against similar vulnerabilities in other kernel components.