Path Traversal in Stable Diffusion WebUI

CVE-2026-77814 is a path traversal vulnerability residing in the scripts/iib/api.py file of the Stable Diffusion WebUI. The vulnerability stems from an insecure implementation of the is_path_trusted function, which performs a prefix check using path.startswith(parent_path) without appending a path separator. Consequently, if /data/images is the intended authorized directory, an attacker can bypass this restriction by requesting a path that starts with the same string, such as /data/images_private/secret.txt.

The security control is governed by get_enable_access_control in scripts/iib/tool.py. It is active when IIB_ACCESS_CONTROL is set to 'enable', or when the WebUI is exposed via --share, --ngrok, --listen, or --server_name flags. Deployments using these network-exposure options are vulnerable to unauthorized file disclosure. This flaw is critical for defenders because it allows attackers to bypass intended file system confinement to retrieve sensitive configuration or system files.

Impact

Successful exploitation allows unauthenticated remote attackers to perform path traversal and access files outside of the intended web root. This leads to the disclosure of sensitive data, such as system configuration files or other private assets reachable by the user account running the WebUI service. The risk is elevated in shared or network-exposed environments where the WebUI is intentionally configured to listen on external interfaces.

Recommendation

• Upgrade Stable Diffusion WebUI to a version that applies the fix, which uses os.sep to enforce directory boundaries during path validation.
• Until patched, restrict network access to the WebUI interface using a firewall or VPN to prevent exploitation of the path traversal logic in network-exposed deployments.
• Audit logs for HTTP requests containing directory traversal sequences or attempts to access directories that share a common prefix with authorized storage paths.
• Disable IIB_ACCESS_CONTROL if the functionality is not required or if the risk cannot be mitigated through network isolation.