CVE-2026-100395
Description
A flaw was found in LXC. When a privileged user or process clones an untrusted container, LXC follows symbolic links (symlinks) while updating the hostname in the target container file system. An attacker with control over the source container can craft a symlink targeting files outside the destination directory. This flaw allows the privileged process to overwrite and truncate arbitrary files on the host, leading to data corruption or a denial of service.
Statement
Red Hat Product Security has determined that this vulnerability does not affect any currently supported Red Hat product. This assessment may evolve based on further analysis and discovery. For more information about this vulnerability and the products it affects, please see the linked references.
Mitigation
Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability.
--- CME Mitigation Guidance (2026-11-06) ---
Disclaimer: The following mitigation solutions are provided as a courtesy, pending the application of an official patch. This content was generated utilizing AI tools in conjunction with data from https://cmetaxonomy.org. Customers are advised to independently evaluate and test these temporary mitigations within their own infrastructure.
The highest-value action is to confine path resolution to the container root filesystem using openat2 with RESOLVE_IN_ROOT when updating container files during clone operations in LXC: upgrade to the fixed Lxc builds, which open the destination container root directory and resolve etc/hostname using openat2 with RESOLVE_IN_ROOT and O_TRUNC to prevent symlinks from escaping the rootfs, closing all 2 injection vectors (crafted symlink at etc/hostname pointing to a host file, crafted symlink in intermediate path components pointing outside destination rootfs). Until patched, this is only a concern on Linux systems running privileged lxc-copy or liblxc clone() operations as root on untrusted containers — Unprivileged container use and container managers with independent cloning implementations are unaffected — so Use the LXC_CLONE_KEEPNAME flag (-K) when cloning untrusted containers to bypass the hostname update, and avoid executing container clone operations with host root privileges. As a compensating measure, Configure auditd to log file modification syscalls originating from lxc-copy to detect unauthorized writes to host files, Run SELinux in enforcing mode to restrict file write access for container management domains outside the rootfs, Deploy EDR monitoring to detect anomalous truncation or modification of host files by container utility processes, Employ Falco or eBPF runtime security to detect anomalous writes to sensitive host configuration files during cloning, and Use AIDE file integrity monitoring to detect unexpected changes and truncation of monitored host system files. These controls limit blast radius and contain exploitation, but they do not fix the underlying symlink-following defect — apply the upstream patch to fully remediate.
Highest-impact CME: CME-1301 Path Traversal Prevention (Canonicalization) (high)
Understanding the Weakness (CWE)
Confidentiality,Integrity,Access Control
Technical Impact: Read Files or Directories; Modify Files or Directories; Bypass Protection Mechanism
An attacker may be able to traverse the file system to unintended locations and read or overwrite the contents of unexpected files. If the files are used for a security mechanism then an attacker may be able to bypass the mechanism.
Other
Technical Impact: Execute Unauthorized Code or Commands
Windows simple shortcuts, sometimes referred to as soft links, can be exploited remotely since a ".LNK" file can be uploaded like a normal file. This can enable remote execution.
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