CVE-2026-93320 in BuildKit
Summary
by MITRE • 10/05/2026
BuildKit may be tricked into performing file actions with special file inodes where regular files are expected. Special files may block operations or, on rootful workers, allow unintended host device access.
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Analysis
by VulDB Data Team • 10/05/2026
The vulnerability identified within BuildKit represents a significant security flaw related to the handling of filesystem inodes during container image building processes. BuildKit is a core component used for constructing OCI-compliant images and serves as the backend for many popular build tools such as Docker Buildx and Kaniko. The fundamental issue lies in how the system interprets file types when executing operations that assume standard regular files are present. Specifically, an attacker or malicious input can exploit this by introducing special file inodes into the build context where a normal file is expected. This discrepancy arises because the underlying logic does not sufficiently validate whether the inode corresponds to a regular file before proceeding with subsequent actions, thereby bypassing critical safety checks designed to prevent unintended side effects.
From a technical perspective, the flaw allows for the manipulation of special files such as block devices, character devices, or named pipes within the build environment. When BuildKit processes these entries under rootful worker conditions, it may inadvertently grant access to host-level resources that should remain isolated from the containerized build process. This behavior violates the principle of least privilege and breaks the expected isolation boundaries between the builder and the underlying host system. The operational impact is severe because an attacker who can influence the contents of a Dockerfile or supply malicious build contexts could potentially read sensitive data, modify critical system files, or execute arbitrary commands on the host machine by leveraging these unintended device accesses. This scenario effectively transforms a routine image building task into a potential vector for privilege escalation and lateral movement within infrastructure environments.
This vulnerability aligns closely with CWE-20 Improper Input Validation, as the root cause is the failure to rigorously check file types before processing them. Furthermore, it relates to CWE-78 OS Command Injection in contexts where special files are used to bypass command sanitization mechanisms or trigger unintended system calls. In terms of offensive security frameworks, this behavior can be mapped to ATT&CK technique T1059 Command and Scripting Interpreter if the exploit leads to arbitrary code execution, or T1217 Browser Information Discovery if it is leveraged for reconnaissance purposes within a compromised build environment. The lack of strict inode type verification creates an opportunity for attackers to subvert security controls that rely on file extension checks or basic path traversal protections, which are often insufficient against sophisticated special file manipulation attacks.
Mitigation strategies must focus on enforcing stricter validation at the input layer and enhancing runtime isolation mechanisms. Developers should implement explicit checks to ensure that only regular files are processed in contexts where such assumptions hold true, rejecting any entries identified as block devices, character devices, or other special inode types during the build context preparation phase. Additionally, running BuildKit with rootless workers significantly reduces the risk profile by limiting the privileges available to the builder process, thereby preventing access to host-level device nodes even if they are inadvertently referenced. Security teams should also audit their CI/CD pipelines for any custom scripts or Dockerfiles that might accept untrusted input without proper sanitization and apply patches provided in subsequent releases of BuildKit that address this inode handling logic. Regular updates to the underlying container runtime and build tools are essential to ensure these protections remain effective against evolving attack techniques.