CVE-2026-109596 in Hugo
Summary
by MITRE • 10/13/2026
Hugo from v0.162.0 before v0.167.0 contains an improper link resolution vulnerability that lets malicious themes or modules expose files outside their root via nested-mount ancestor directories. Attackers controlling a theme can place a symlink or NTFS junction at a virtual ancestor directory, causing resources.Match to list and publish local files during builds.
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Analysis
by VulDB Data Team • 10/13/2026
The Hugo static site generator, specifically versions ranging from v0.162.0 up to but not including v0.167.0, contains a critical improper link resolution vulnerability that allows for unauthorized access to file system resources outside the intended project root directory. This flaw stems from how the application handles path traversal and symbolic links during the build process when nested mounts are utilized in theme or module configurations. The core issue lies in the failure of Hugo's resource matching logic to properly validate whether a resolved path remains within the designated safe boundaries after following symlinks or NTFS junctions that point to ancestor directories outside the project scope.
In this vulnerability scenario, an attacker who has control over a theme or module associated with a Hugo site can manipulate the directory structure by placing a symbolic link or an NTFS junction at a virtual ancestor directory within the theme's file hierarchy. When Hugo processes these files during the build phase, it resolves the links and subsequently lists and publishes local files that reside in directories above the project root. This behavior effectively bypasses the isolation mechanisms designed to keep static site generation confined to the specific working directory, leading to the exposure of sensitive system files or other data located on the host machine where Hugo is executed.
The operational impact of this vulnerability is significant for users who build sites using themes from untrusted sources or modules that have not been thoroughly vetted. By exploiting this flaw, an attacker can achieve arbitrary file read access relative to the execution context of the Hugo process. This could result in the leakage of configuration files containing secrets, source code repositories, personal documents, or other confidential information stored on the server's filesystem. The vulnerability is particularly dangerous because it leverages standard operating system features like symbolic links and NTFS junctions, which are often used legitimately for convenience but can be weaponized here due to insufficient path validation in Hugo’s resource matching engine.
From a classification perspective, this issue aligns with CWE-22: Improper Limitation of a Pathname to a Restricted Directory, as the application fails to restrict access to files outside the intended directory structure. Additionally, it relates to CWE-59: Improper Link Resolution Before File Access, highlighting the failure to validate links prior to using them for file operations. In terms of attack vectors and tactics, this vulnerability can be mapped to ATT&CK technique T1083: File and Directory Discovery, where an adversary uses discovered paths to locate sensitive information, and potentially T1564: Hidden Files and Directories if the symlink is used to obscure the path traversal mechanism.
To mitigate this risk, users should immediately upgrade Hugo to version v0.167.0 or later, which includes patches for improper link resolution logic. Until an upgrade is feasible, administrators should enforce strict security policies regarding theme sources, ensuring that only trusted and audited themes are used in production environments. It is also advisable to run Hugo builds within restricted containers or sandboxed environments with limited file system access permissions, thereby reducing the blast radius if a malicious theme attempts to exploit this vulnerability. Regularly reviewing dependency updates and applying patches promptly remains essential for maintaining the integrity of static site generation pipelines.