CVE-2026-86334 in LXD
Summary
by MITRE • 09/28/2026
Path traversal in the CLI client image export and copy functionality in Canonical LXD from 4.0.2 before 4.0.14, 5.0.10, 5.21.8, and 6.10 on all platforms allows a remote malicious or machine-in-the-middle image server to overwrite arbitrary local files and execute code on the client system via a crafted Content-Disposition header filename parameter during unified image export or copy operations into a local directory target.
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Analysis
by VulDB Data Team • 09/28/2026
The vulnerability identified in Canonical LXD represents a critical path traversal flaw within the command-line interface components responsible for handling image exports and copies. This security defect affects multiple versions of the software, specifically those ranging from 4.0.2 up to but not including 4.0.14, as well as version 5.0.10, 5.21.8, and 6.10 across all supported operating systems. The core issue stems from insufficient validation of filenames provided by external image servers during the unified image export or copy operations. When a user initiates an operation to retrieve an image into a local directory target, LXD relies on metadata sent by the remote server, particularly within the Content-Disposition header's filename parameter, to determine where and how to save the extracted files. The application fails to properly sanitize these filenames before processing them for file system operations, allowing malicious actors to inject path traversal sequences such as dot-dot-slash into the filename string.
This technical flaw enables a remote attacker or a machine-in-the-middle actor controlling an image server to manipulate the destination paths of exported files. By crafting a Content-Disposition header with a specially constructed filename containing relative directory navigation characters, the attacker can force LXD to write files outside the intended local target directory. This capability effectively bypasses sandboxing and isolation boundaries that are typically enforced by container runtimes like LXC/LXD. The operational impact is severe, as it allows for arbitrary file overwrite on the host system where the vulnerable client software resides. An adversary could replace critical configuration files, scripts, or binaries with malicious content, thereby gaining unauthorized access to sensitive data or establishing persistence mechanisms that survive subsequent reboots and container restarts.
The exploitation of this vulnerability aligns closely with Common Weakness Enumeration category CWE-22, which defines Improper Limitation of a Pathname to a Restricted Directory. In practical terms, the attacker leverages this weakness to escape the intended directory scope, leading directly to CWE-94, Code Injection, if the overwritten files are subsequently executed by system processes or user accounts with elevated privileges. Furthermore, from an adversarial tactics perspective, this behavior corresponds to techniques found in the MITRE ATT&CK framework under Initial Access and Persistence vectors, specifically those involving file manipulation for privilege escalation or lateral movement within a compromised environment. The risk is exacerbated when users interact with untrusted image registries or operate in network environments where traffic interception is feasible, as it transforms routine administrative tasks into potential attack surfaces.
Mitigation strategies must prioritize immediate software updates to address the root cause of this input validation failure. Administrators should upgrade Canonical LXD to version 4.0.14 or later for the 4.x branch, version 5.0.11 or later for the 5.x branch, version 5.21.9 or later for the 5.21 series, and version 6.11 or later for the 6.x line. These releases contain patches that enforce strict sanitization of filenames derived from external headers, ensuring that only alphanumeric characters, hyphens, underscores, and dots are permitted in destination paths without allowing directory traversal sequences. In addition to patching, organizations should implement network segmentation policies to restrict access to image servers within trusted internal networks whenever possible. Monitoring logs for unusual file system write operations outside of expected directories can also aid in the early detection of exploitation attempts before significant damage occurs.