CVE-2026-95838 in containerd
Summary
by MITRE • 10/12/2026
containerd is an open-source container runtime. Prior to 1.7.35, 2.0.12, 2.2.8, and 2.3.5, containerd's layer unpack handler repeatedly traverses directories for certain opaque whiteout configurations. A malicious image layer can trigger repeated directory traversals while opaque whiteouts are processed. Pulling or importing the image can consume CPU, delay container startup, and reduce image-pull concurrency for unrelated deployments. This issue is fixed in versions 1.7.35, 2.0.12, 2.2.8, and 2.3.5.
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Analysis
by VulDB Data Team • 10/12/2026
The vulnerability identified within the containerd open-source container runtime represents a significant resource exhaustion risk stemming from inefficient handling of specific filesystem operations during image layer processing. Containerd serves as a critical component in modern container orchestration ecosystems, responsible for managing the lifecycle of containers and interacting with underlying operating system primitives to unpack OCI-compliant images. The flaw resides specifically within the layer unpack handler, which is tasked with translating the compressed layers of an imported or pulled container image into a usable filesystem structure on the host node. This process involves interpreting special files known as whiteouts, which are used in union file systems like OverlayFS to indicate that certain directories or files from lower layers should be hidden or removed when constructing the final merged view for the container runtime.
The technical root cause of this vulnerability is an infinite or excessively deep recursive traversal triggered by malformed opaque whiteout configurations within a maliciously crafted image layer. In standard OCI image specifications, opaque whiteouts are used to signal that all files in a directory should be hidden unless explicitly present in upper layers. The flawed implementation fails to properly bound the depth or complexity of these traversals when encountering specific edge cases involving nested directories and whiteout markers. Instead of terminating early or applying strict limits on recursion depth, the handler repeatedly scans through directories, leading to an exponential increase in computational work relative to the size and structure of the malicious payload. This behavior effectively creates a logic error that can be exploited by attackers who construct images with deeply nested structures containing specific opaque whiteout patterns designed to maximize traversal cycles.
From an operational perspective, this vulnerability poses a severe availability risk through resource exhaustion rather than direct code execution or privilege escalation. When a user pulls or imports such a malicious image, the containerd process consumes disproportionate amounts of CPU resources due to the endless directory traversals. This excessive consumption can lead to significant delays in container startup times for legitimate workloads and may cause timeouts during the pull operation itself. Furthermore, because containerd often manages multiple concurrent operations across many containers on a single host, the resource hogging caused by this vulnerability reduces overall image-pull concurrency. This degradation affects unrelated deployments sharing the same runtime instance, potentially causing cascading failures in orchestration systems like Kubernetes where timely scheduling and startup of pods are critical for service reliability.
The impact aligns with common attack patterns involving denial-of-service via computational exhaustion. In terms of industry standards, this vulnerability maps to CWE-400, which covers Uncontrolled Resource Consumption, specifically the scenario where an attacker can cause a system to consume excessive resources through crafted input that triggers inefficient algorithmic behavior. Additionally, from the perspective of the MITRE ATT&CK framework for container security, this flaw relates to techniques involving resource hijacking or denial-of-service against container runtimes. It highlights the importance of validating and sanitizing image contents before they are processed by the runtime engine, as untrusted images can exploit internal logic flaws in unpacking mechanisms to disrupt host stability.
Mitigation strategies primarily involve upgrading to patched versions of containerd where this traversal limit has been corrected. The issue is resolved in versions 1.7.35, 2.0.12, 2.2.8, and 2.3.5, which implement stricter bounds on directory recursion during whiteout processing. Organizations relying on these older versions should prioritize immediate updates to prevent potential denial-of-service attacks via malicious container images. In environments where upgrading is not immediately feasible, implementing strict image scanning policies that reject layers with suspiciously deep or complex opaque whiteout structures can provide a layer of defense. Additionally, configuring resource limits for the containerd process itself using cgroups can help mitigate the impact by preventing any single operation from monopolizing host CPU resources indefinitely, thereby preserving stability for other critical workloads running on the same infrastructure.