CVE-2026-88264 in crun
Summary
by MITRE • 09/10/2026
A flaw was found in crun. When the container configuration does not give /dev a dedicated mount, terminal setup can redirect /dev/console onto an attacker-controlled path, including via the read-only-rootfs bind-mount fallback. Affected versions are crun 1.29.1 and earlier. Default configurations that mount a fresh /dev are not exposed. No fixed release is available yet.
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Analysis
by VulDB Data Team • 09/10/2026
The vulnerability identified in crun represents a significant security risk within containerized environments, specifically targeting the initialization of terminal devices when specific configuration constraints are present. Crun serves as an OCI-compliant container runtime that executes containers using Linux namespaces and cgroups to provide isolation for processes. The core issue arises during the setup phase where the runtime attempts to configure standard file descriptors such as stdin, stdout, and stderr by mapping them to appropriate device nodes within the /dev directory of the container's root filesystem. This process is critical because it determines how a user or application interacts with the terminal interface inside the isolated environment. When the container configuration explicitly omits a dedicated mount for /dev, crun employs fallback mechanisms to ensure that necessary devices are available. One such mechanism involves bind-mounting files from the host system into the container's filesystem structure if certain conditions regarding read-only root file systems are met.
The technical flaw lies in how these fallback mechanisms handle path resolution and validation before performing mount operations. Specifically, when /dev is not mounted separately, crun may redirect /dev/console to a location controlled by an attacker who has write access to the container's filesystem or can influence the bind-mount targets through other means. This redirection allows for arbitrary file overwrites on the host system if the path resolves outside of expected boundaries or if the mount operation lacks sufficient restrictions. The vulnerability exploits the assumption that paths provided during configuration are safe and correctly scoped within the container's namespace. By manipulating this process, an attacker can potentially overwrite critical system files on the underlying host machine, leading to a complete compromise of the host's integrity. This is particularly dangerous because it bypasses typical isolation boundaries expected in container security models.
From an operational perspective, this vulnerability impacts environments where containers are configured with read-only root file systems but lack explicit /dev mounts. Such configurations are often used to enhance security by preventing modifications to application binaries and configuration files within the container. However, without a dedicated /dev mount, crun's fallback logic becomes a vector for privilege escalation or host compromise. The impact extends beyond simple data leakage; it allows an attacker with access to modify critical system components on the host, potentially installing backdoors, disabling security controls, or achieving persistent access. Since default configurations that mount a fresh /dev are not affected, the risk is primarily associated with custom or hardened container setups where administrators have intentionally removed standard device mounts for specific reasons, inadvertently exposing this flaw.
This vulnerability aligns with CWE-284 Improper Access Control and CWE-732 Incorrect Permission Assignment for Critical Resource, as it involves misconfigured permissions that allow unauthorized modification of system resources. In terms of the MITRE ATT&CK framework, this behavior corresponds to techniques involving persistence or privilege escalation through container escape mechanisms, specifically leveraging host resource access via improper configuration management. The lack of a fixed release at the time of disclosure necessitates immediate attention from security teams managing affected versions up to 1.29.1 and earlier. Mitigation strategies should focus on ensuring that containers do not rely on fallback mount behaviors for critical device nodes unless strictly necessary, or alternatively, applying strict path validation checks within container runtimes before executing bind mounts. Administrators are advised to audit their container configurations to ensure /dev is properly mounted as a separate filesystem rather than relying on host-based fallbacks until an official patch is released by the crun maintainers.