CVE-2026-58090 in FreeBSD
Summary
by MITRE • 08/26/2026
The SOCK_STREAM receive path in the unix socket implementation failed to fully detach control messages from the socket buffer before processing them. Some error paths would free those messages, leaving freed data mbufs in the receive socket buffer.
An unprivileged local user can exploit this use-after-free to escalate privileges.
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Analysis
by VulDB Data Team • 08/26/2026
The vulnerability resides within the Unix domain socket implementation of the operating system kernel, specifically affecting the SOCK_STREAM receive path where control messages are processed. Control messages, often referred to as ancillary data or SCM_RIGHTS in POSIX systems, allow for the transfer of file descriptors and other critical metadata between processes over a local socket connection. The core technical flaw is a failure in memory management logic during the detachment phase. When receiving these complex message structures, the kernel must carefully parse the control buffer, extract the relevant information, and then safely release or detach the underlying data mbufs from the socket's internal receive queue to prevent memory leaks or corruption. In this specific instance, certain error handling paths within the code failed to properly execute this detachment step before proceeding with further processing or cleanup routines.
This incomplete detachment leads directly to a use-after-free condition, which is classified under CWE-416 in the Common Weakness Enumeration standard. The sequence of events begins when an application sends a message containing control data through a Unix domain socket. As the kernel processes this incoming stream, it allocates memory buffers (mbufs) to hold the payload and ancillary data. Under normal circumstances, once the data is parsed and passed to the user-space process or handled internally, these buffer references are cleared from the socket's receive queue. However, due to the defect in specific error paths, the kernel proceeds to free the control message structures while leaving dangling pointers to those freed memory regions still present within the socket buffer structure. This creates a state where valid internal data structures reference memory that has already been returned to the system allocator and is potentially available for reallocation by other processes or subsystems.
The operational impact of this vulnerability is severe, primarily because it allows an unprivileged local user to escalate privileges to root level on the affected system. By carefully crafting a series of socket operations and triggering the specific error conditions that lead to the use-after-free state, an attacker can manipulate how the kernel reallocates the freed memory. If the attacker can control what data is written into those reallocated mbufs before they are accessed again by the vulnerable code path, they can achieve arbitrary read or write primitives within the kernel address space. This capability enables the modification of critical kernel structures, such as credential objects or process tables, effectively bypassing all standard access controls and security boundaries enforced by the operating system.
From a threat modeling perspective, this vulnerability aligns with MITRE ATT&CK technique T1068, which covers Exploitation for Privilege Escalation. It also relates to T1203, Software Vulnerability Management failures where unpatched flaws are leveraged in local attacks. The attack vector is classified as Local (L) and requires low complexity because it does not require specific user interaction beyond the ability to create sockets and send data, which is a fundamental capability of any standard process on Unix-like systems. This makes the vulnerability particularly dangerous in multi-user environments or containerized deployments where isolation boundaries are critical for security posture.
Mitigation strategies must focus primarily on applying vendor-provided patches that correct the memory management logic within the unix socket implementation. System administrators should prioritize updating kernel packages to versions that include fixes for this specific use-after-free condition. Until patching is possible, defensive measures can be limited due to the low-level nature of the exploit; however, restricting local user access and enforcing strict container isolation policies can reduce the attack surface. Additionally, enabling Kernel Address Space Layout Randomization (KASLR) may increase the difficulty for attackers by making it harder to predict memory addresses required for successful exploitation, although this is not a definitive fix given that modern use-after-free exploits often rely on information disclosure or heap grooming techniques that mitigate such protections. Regular auditing of system logs for unusual socket activity and ensuring timely application of security updates remain essential practices for maintaining the integrity of systems susceptible to kernel-level privilege escalation vulnerabilities.