CVE-2026-61712 in BuildKit
Summary
by MITRE • 08/19/2026
BuildKit is a toolkit for converting source code to build artifacts in an efficient, expressive and repeatable manner. Prior to 0.31.1, BuildKit read attacker-controlled /etc/passwd and /etc/group files without an upper bound while resolving a username to a user identifier or group identifier in executor/oci/user.go and solver/llbsolver/ops/user_linux.go. A malicious base image or build could provide oversized files that exhausted memory during user resolution and caused out-of-memory termination of the buildkitd process. This issue is fixed in version 0.31.1.
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Analysis
by VulDB Data Team • 08/19/2026
BuildKit serves as a critical component in modern containerized development workflows, functioning as a toolkit designed to convert source code into build artifacts with efficiency, expressiveness, and repeatability. The software operates by parsing Dockerfiles or other build specifications and executing the necessary steps to produce final images. A significant security vulnerability was identified within versions prior to 0.31.1 concerning how BuildKit handles user identity resolution during the build process. Specifically, when resolving a username or group name provided in a build specification into its corresponding numeric user identifier (UID) or group identifier (GID), the system interacts with standard Unix configuration files such as /etc/passwd and /etc/group located within the build context or base image layers.
The core technical flaw lies in the lack of input validation regarding the size of these identity mapping files. The functions executor/oci/user.go and solver/llbsolver/ops/user_linux.go were designed to read attacker-controlled instances of /etc/passwd and /etc/group without enforcing an upper bound on file length or content volume. In a typical Linux environment, these files are relatively small text files containing user account information. However, because BuildKit does not limit the size of data it processes during this resolution phase, a malicious actor can craft a base image that includes deliberately oversized versions of these files. This constitutes an uncontrolled resource consumption scenario where the system attempts to load and parse excessively large amounts of data into memory.
The operational impact of this vulnerability is severe, primarily manifesting as a denial-of-service condition through out-of-memory termination. When BuildKit encounters these oversized /etc/passwd or /etc/group files during user resolution, it consumes an excessive amount of RAM relative to the available system resources. This unbounded memory allocation can quickly exhaust the memory capacity of the host machine running the buildkitd process. Consequently, the operating system's out-of-memory killer may terminate the buildkitd process abruptly, disrupting ongoing builds and potentially affecting other services sharing the same resource pool. This vulnerability allows a malicious base image or build specification to effectively crash the build infrastructure without requiring any additional privileges beyond those needed to submit a build job.
From a classification perspective, this issue aligns with CWE-787: Out-of-bounds Read and CWE-400: Uncontrolled Resource Consumption. The failure to validate input size before processing leads directly to resource exhaustion. In the context of the MITRE ATT&CK framework, this vulnerability can be leveraged for Impact via Denial of Service, specifically targeting system availability by exhausting computational resources such as memory or CPU cycles. Attackers do not need to execute arbitrary code on the host; simply providing a malformed build artifact is sufficient to trigger the failure condition.
Mitigation strategies focus primarily on upgrading to version 0.31.1 or later, where this issue has been resolved through improved input validation and size limiting mechanisms within the user resolution logic. Organizations relying on BuildKit should ensure their CI/CD pipelines are updated to use patched versions of the toolkit. Additionally, implementing strict image scanning policies can help detect base images that contain abnormally large system configuration files before they reach the build stage. While upgrading is the definitive fix, temporary mitigations might include restricting the resources available to buildkitd processes via cgroups or container limits to prevent a single malicious build from exhausting all host memory, although this does not address the root cause and may impact legitimate workloads.