CVE-2026-100692: 
Grafana vulnerability analysis and mitigation

CVE-2026-100692 is a symlink traversal vulnerability (CWE-59) in Hugo, the open-source static site generator, that allows unauthenticated attackers to read arbitrary files from the build system during site generation. Affecting Hugo versions after v0.123.0 and before v0.166.0, the flaw enables a malicious theme or vendored module to place a symlink at a mount root (e.g., themes/mytheme/assets -> /some/dir/outside), bypassing Hugo's intended confinement that restricts theme/module mounts to local paths. The vulnerability was published on September 26, 2026, and credited to researcher DONG2209. It carries a CVSS v3.1 score of 7.5 (High) and a CVSS v4.0 score of 8.7 (High) (GitHub Advisory, Github Advisory).

The root cause is improper link resolution before file access (CWE-59): Hugo's symlink confinement logic checked whether a path was within the mount root boundary, but failed to verify whether the mount root itself — or intermediate directories between the mount root and the module directory — was a symlink pointing outside the project. This allowed a theme or vendored module stored in themes/ to include a symlink at the mount root level (e.g., themes/mytheme/assets -> /etc/ or another sensitive directory), which Hugo would then follow during build operations such as resources.Get, resources.Match, and static mount publishing to public/. Modules fetched via Go modules are not affected because Go module zip archives cannot contain symlinks by design. The attack requires the ability to commit or supply a malicious theme or vendored module to the target Hugo project (GitHub Advisory, Github Advisory).

Successful exploitation allows an attacker who can introduce a malicious theme or vendored module into a Hugo project to read arbitrary files from the build system — including sensitive configuration files, credentials, or private data — and potentially publish them to the generated public/ output directory, making them publicly accessible. The impact is limited to confidentiality (no integrity or availability impact), but the exposed files could include secrets, environment variables, or other sensitive build-system content. This is particularly relevant in CI/CD pipelines where Hugo builds are automated and the build environment may contain sensitive credentials (GitHub Advisory, Feedly).

There is no public proof-of-concept exploit and no evidence of in-the-wild exploitation at the time of disclosure. The EPSS score is 0.0, and the vulnerability is not listed in the CISA Known Exploited Vulnerabilities (KEV) catalog. Exploitation requires the ability to commit a malicious theme or vendored module to the target repository, which limits the attack surface to supply-chain scenarios or cases where untrusted themes are used (GitHub Advisory, Github Advisory).

1. Identify a target: Find a Hugo project (v0.123.1–v0.165.x) that uses themes or vendored modules checked into the repository, particularly in CI/CD pipelines where the build environment may contain sensitive files.
2. Craft a malicious theme or module: Create or modify a theme directory (e.g., themes/mytheme/) and replace a mount-root directory (e.g., themes/mytheme/assets) with a symlink pointing to a sensitive directory outside the project root (e.g., ln -s /etc themes/mytheme/assets or ln -s /home/user/.ssh themes/mytheme/assets).
3. Introduce the malicious theme: Commit the theme containing the symlink to the target repository, or supply it as a vendored module. This could be achieved via a pull request, a compromised dependency, or direct repository access.
4. Trigger a Hugo build: Wait for or trigger a Hugo site build (e.g., via CI/CD pipeline). During the build, Hugo follows the symlink and makes files behind it accessible through resources.Get, resources.Match, or static mounts.
5. Exfiltrate data: Reference the symlinked files in templates or static mounts so they are copied to the public/ output directory, then retrieve them from the published site or build artifacts (GitHub Advisory).

• File System: Presence of symlinks at mount root directories within themes/ (e.g., themes/<themename>/assets, themes/<themename>/static) pointing to paths outside the project root; symlinks in vendored module directories under vendor/ pointing to external paths.
• File System: Unexpected files in the public/ output directory that correspond to system files (e.g., /etc/passwd, SSH keys, .env files) or files from outside the project directory.
• Logs: Hugo build logs referencing files from unexpected absolute paths during resources.Get or resources.Match operations.
• CI/CD: Build artifacts or deployed site content containing sensitive system files not intentionally included in the project (GitHub Advisory).

Upgrade Hugo to v0.166.0 or later, where symlinked mount roots and symlinked directories between the mount root and the module directory are treated as non-existent for all modules, including the main project. As a workaround for environments that cannot immediately upgrade, manually inspect themes/ and vendored module directories for symlinks at mount roots before running any build (e.g., using find themes/ -maxdepth 3 -type l), and replace any such symlinks with explicit mount configurations in hugo.toml. Modules fetched via Go modules do not require remediation as they cannot contain symlinks (GitHub Advisory, Github Advisory).