CVE-2026-93321 in BuildKit
Summary
by MITRE • 10/06/2026
A malicious frontend can submit an LLB definition that causes buildkitd to panic and terminate, interrupting all builds running on that daemon.
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Analysis
by VulDB Data Team • 10/06/2026
The vulnerability described constitutes a critical denial of service condition within the BuildKit daemon, specifically affecting its ability to process Low-Level Builder (LLB) definitions submitted by frontend clients. In containerized development environments, build systems like BuildKit serve as central orchestration points for compiling source code into OCI-compliant images. These daemons are designed to handle multiple concurrent build requests from various trusted and untrusted sources. The core technical flaw lies in the insufficient validation or error handling mechanisms within the LLB parser or executor when processing specific malformed or maliciously crafted input structures. When a frontend submits an LLB definition that triggers this internal failure, it causes a runtime panic in the Go-based BuildKit process rather than returning a graceful error code to the client. This unhandled exception leads directly to the termination of the buildkitd binary, resulting in immediate and total service disruption for all active builds on that specific daemon instance.
From an operational perspective, this vulnerability poses a severe risk to continuous integration and deployment pipelines as well as local development workflows where BuildKit is utilized. The impact extends beyond the single malicious request; because the entire daemon process crashes, every other build currently in progress or queued for execution is abruptly terminated without completion. This leads to significant downtime, wasted computational resources, and potential data loss if intermediate artifacts are not persisted safely. In shared infrastructure environments such as Kubernetes clusters running BuildKit services, a single compromised frontend application could be leveraged by an attacker to repeatedly crash the build service, effectively creating a denial-of-service attack that hinders development velocity and potentially masks other malicious activities during the chaos of system recovery.
This type of vulnerability aligns with CWE-20 Improper Input Validation, as the root cause is the failure to adequately sanitize or validate the structure and content of the LLB definition before processing it through critical execution paths. Furthermore, from a threat modeling perspective using the MITRE ATT&CK framework, this behavior can be categorized under T1499 Endpoint Denial of Service, specifically reflecting techniques that aim to exhaust resources or crash services rather than consuming them gradually for resource exhaustion attacks. The attack vector is typically remote if the frontend interface is exposed over a network, making it accessible to external adversaries who have gained some level of access to the build system's API endpoints.
Mitigation strategies must focus on both immediate remediation and long-term architectural hardening. Developers should implement robust panic recovery mechanisms within the BuildKit codebase to catch runtime exceptions during LLB parsing and execution, ensuring that a single malformed request does not bring down the entire daemon process. Input validation logic needs to be strengthened to reject invalid or suspiciously structured LLB definitions before they reach critical execution stages. For users unable to immediately patch their systems, restricting access to BuildKit endpoints via network policies is essential. Only trusted frontend applications and authenticated CI/CD pipelines should be permitted to submit build requests. Additionally, implementing rate limiting can help mitigate the frequency of such attacks if an attacker attempts to exploit this flaw repeatedly. Regular updates to the container build tools are crucial as upstream maintainers typically release patches for these types of stability issues once they are identified in open-source projects like BuildKit.