CVE-2026-49415 in FreeBSD
Summary
by MITRE • 08/19/2026
During execve(2) of a SUID binary, the new virtual address space is installed before the process credentials are updated. During this window, a process running as the same user can access the target process's memory via procfs or linprocfs, because the kernel's debugging permission check still saw the original credentials.
An unprivileged local user can exploit this race to modify the address space of a SUID binary before its credentials are elevated, potentially gaining full control of the affected system.
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Analysis
by VulDB Data Team • 08/20/2026
The vulnerability described constitutes a critical privilege escalation flaw rooted in the atomicity and ordering of operations within the kernel's process execution subsystem. Specifically, when an executable file is loaded via the execve system call for a binary with Set-User-ID (SUID) permissions set, the operating system performs several sequential steps to transition the executing process from its original unprivileged state to that of the target user identity defined in the binary's metadata. The core technical flaw lies in the temporal gap between installing the new virtual address space and updating the process credentials. During this narrow window, the kernel has already mapped the memory pages for the SUID program into the process's address space but has not yet switched the security context to reflect the elevated privileges of the target user ID.
This race condition creates a specific attack surface that can be exploited by an unprivileged local user who shares the same initial user identity as the attacker or is otherwise positioned to monitor sibling processes. By leveraging high-precision timing techniques, such as polling via procfs or linprocfs interfaces, an attacker can detect this precise moment in the execution lifecycle. Because the kernel's debugging and memory access permission checks rely on the current credentials of the process, and those credentials have not yet been updated to reflect the SUID status, the security subsystem incorrectly permits access based on the original, lower-privilege identity. Consequently, an attacker can inject malicious code or modify data within the address space of the target SUID binary before it gains its elevated privileges.
The operational impact of this vulnerability is severe, as it allows for arbitrary code execution with root-level permissions if the targeted SUID binary runs as the superuser. By modifying the memory layout or injecting shellcode into the process during this window, an attacker can effectively hijack the control flow of the privileged program once credentials are finally updated. This results in a complete compromise of system integrity and confidentiality, granting the attacker full administrative control over the affected host. The flaw undermines the fundamental security model that relies on atomic credential transitions to prevent such mid-execution tampering, exposing systems to local privilege escalation attacks without requiring any prior elevated privileges or remote access vectors.
Mitigation strategies must focus on ensuring that memory mapping and credential updates are performed atomically or with strict serialization to eliminate this race window. Kernel developers should enforce a sequence where process credentials are updated immediately upon the decision to execute a SUID binary, before the new address space is fully committed and accessible for modification by other processes. Alternatively, implementing stricter checks on procfs access during execve transitions can prevent unauthorized memory inspection of processes in flux. System administrators should also consider restricting local user privileges or applying kernel patches that enforce atomicity in credential handling until a permanent code fix is deployed. This issue highlights the importance of rigorous verification of security state transitions in operating system kernels to prevent timing-based exploitation vectors.