CVE-2026-3038 in FreeBSD
Summary
by MITRE • 03/09/2026
The rtsock_msg_buffer() function serializes routing information into a buffer. As a part of this, it copies sockaddr structures into a sockaddr_storage structure on the stack. It assumes that the source sockaddr length field had already been validated, but this is not necessarily the case, and it's possible for a malicious userspace program to craft a request which triggers a 127-byte overflow.
In practice, this overflow immediately overwrites the canary for the rtsock_msg_buffer() stack frame, resulting in a panic once the function returns.
The bug allows an unprivileged user to crash the kernel by triggering a stack buffer overflow in rtsock_msg_buffer(). In particular, the overflow will corrupt a stack canary value that is verified when the function returns; this mitigates the impact of the stack overflow by triggering a kernel panic.
Other kernel bugs may exist which allow userspace to find the canary value and thus defeat the mitigation, at which point local privilege escalation may be possible.
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Analysis
by VulDB Data Team • 03/17/2026
The vulnerability identified as CVE-2026-3038 resides within the rtsock_msg_buffer() function of a kernel networking subsystem, representing a classic stack buffer overflow condition that demonstrates poor input validation practices in kernel space operations. This function is responsible for serializing routing information into a buffer, a critical operation within the kernel's networking stack that handles communication between userspace applications and kernel routing tables. The flaw manifests when the function copies sockaddr structures into a sockaddr_storage structure located on the stack, assuming that the source sockaddr length field has already been validated through prior checks. However, this assumption proves incorrect as malicious userspace programs can craft specially crafted requests that bypass expected validation mechanisms, creating a scenario where the copy operation exceeds the allocated buffer boundaries by 127 bytes.
The technical execution of this vulnerability begins with a userspace program constructing a malformed routing request that includes an oversized sockaddr structure, which when processed by the rtsock_msg_buffer() function triggers the buffer overflow condition. The specific nature of the overflow targets the stack canary value within the rtsock_msg_buffer() function's stack frame, a security mechanism designed to detect stack corruption and prevent exploitation. When the overflow occurs, it overwrites this critical canary value, which is subsequently verified during function return operations. The verification process immediately triggers a kernel panic, effectively crashing the system and preventing further exploitation attempts. This behavior aligns with CWE-121 Stack-based Buffer Overflow, which describes buffer overflows that occur when data is copied into a stack buffer without proper bounds checking, and demonstrates the fundamental principle of stack canary protection mechanisms.
The operational impact of this vulnerability extends beyond simple denial of service, as it represents a potential pathway for privilege escalation when combined with other kernel vulnerabilities. While the immediate effect is a system crash that prevents exploitation, the vulnerability's existence indicates that kernel developers have not implemented robust input validation for routing socket operations. The fact that this vulnerability affects unprivileged userspace programs means that any user with access to routing socket operations can potentially trigger the exploit, making it particularly concerning for multi-user systems and server environments. The vulnerability's classification under the ATT&CK framework would fall within the Privilege Escalation and Defense Evasion tactics, as it could potentially be leveraged to bypass kernel security protections. The 127-byte overflow size suggests that the attacker has precise control over the amount of data being written beyond the buffer boundary, indicating either a sophisticated attacker or a design flaw that allows for predictable buffer layouts.
The mitigation strategies for this vulnerability primarily focus on immediate kernel patches that implement proper bounds checking for sockaddr length fields before copying operations occur. The recommended approach involves validating the source sockaddr structure length against the expected maximum buffer size before any memory copying operations take place, ensuring that the copy operation cannot exceed allocated buffer boundaries. Additionally, the kernel should implement more robust stack canary verification mechanisms that are resistant to potential information leakage attacks, as the current implementation may be vulnerable to other kernel bugs that could allow userspace to discover canary values. System administrators should also consider implementing monitoring solutions to detect unusual routing socket activity patterns that might indicate exploitation attempts. The vulnerability highlights the importance of defensive programming practices in kernel space, particularly around buffer management and input validation, as even seemingly benign operations like copying socket addresses can become critical security flaws when proper validation is omitted.