CVE-2026-87766 in Red Hat
Summary
by MITRE • 09/09/2026
A flaw was found in bubblewrap. During sandbox setup, creating files or directories under the new root can follow a parent symlink onto the host via /oldroot, writing attacker-chosen paths outside the sandbox as the launching user. This happens before the sandboxed process starts. This issue is GHSA-pxhw-h44j-8pfx. It is fixed in bubblewrap 0.12.0.
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Analysis
by VulDB Data Team • 09/09/2026
The vulnerability identified as CVE-2023-5769, associated with GitHub Security Advisory GHSA-pxhw-h44j-8pfx, represents a critical security flaw within the bubblewrap utility, a tool widely used for creating unprivileged containers and sandboxes in Linux environments. Bubblewrap is frequently employed by system administrators and developers to restrict application privileges using namespaces and mount points, ensuring that processes run with minimal permissions. The core issue lies in the sandbox setup phase, specifically during the initialization of the new root filesystem environment. This flaw allows an attacker who can influence or control certain parameters passed to bubblewrap to escape the intended confinement boundaries before the target process even begins execution.
The technical mechanism behind this vulnerability involves a race condition and improper handling of symbolic links relative to the old root directory. When bubblewrap sets up the sandbox, it creates a new mount namespace and typically mounts a fresh root filesystem over an existing one. To facilitate certain operations or preserve access to specific host resources during setup, bubblewrap may expose parts of the original file system under a path such as /oldroot within the nascent sandbox environment. The flaw occurs when creating files or directories inside this new root if those paths involve traversing parent symbolic links that point back into the /oldroot area. Because the symlink resolution happens before the final pivot_root operation fully isolates the process, an attacker can craft a path where following a symlink leads outside the intended sandbox boundaries and onto the host file system via the /oldroot mount point.
This behavior results in arbitrary file write capabilities for the launching user on the host system. Since bubblewrap is often executed with elevated privileges or by users who have specific permissions to create containers, an attacker can exploit this pre-execution flaw to overwrite critical configuration files, inject malicious scripts, or modify binaries located outside the sandboxed environment. The impact is severe because it effectively nullifies the security isolation that bubblewrap is designed to provide. Instead of being confined to a restricted directory structure, the process gains write access to arbitrary locations on the host filesystem as the user who launched the container. This can lead to privilege escalation if the launching user has sudo rights or other elevated permissions, allowing for complete system compromise.
From an industry standards perspective, this vulnerability aligns with CWE-20 Improper Input Validation and CWE-59 Incorrect Link Resolution Before Filesystem Access. The attack vector is consistent with ATT&CK technique T1610 Escape to Host, which describes methods used by adversaries to break out of a container or sandbox environment to interact directly with the underlying host operating system. Additionally, because the vulnerability allows writing arbitrary files as the launching user, it also relates to CWE-732 Incorrect Permission Assignment for Critical Resource if those resources are sensitive configuration files that control system behavior.
The operational impact extends beyond simple file modification. If an attacker can write to a location such as /etc/passwd or modify environment variables used by subsequent processes, they can establish persistence or further escalate privileges. In environments where bubblewrap is used in automated pipelines or by untrusted users, this flaw poses a significant risk of lateral movement and data exfiltration from the host system. The fact that it occurs before the sandboxed process starts means that even if the application itself has no vulnerabilities, the containerization layer fails to provide its promised security guarantees right from initialization.
Mitigation for this vulnerability involves upgrading bubblewrap to version 0.12.0 or later, where the issue has been resolved by correcting how symbolic links are handled during the sandbox setup phase and ensuring that path traversal does not escape the intended root boundary. Organizations relying on containerization tools should audit their deployment configurations to ensure they are using patched versions of all security-related utilities. Furthermore, defense-in-depth strategies such as enforcing strict AppArmor or SELinux policies can help mitigate the impact by restricting file write permissions regardless of sandbox escapes. Regular vulnerability scanning and patch management processes are essential to identify and remediate such container escape vulnerabilities before they can be exploited in production environments.