CVE-2026-58174: Hermes WebUI Profile Isolation Bypass via Session Import

Technical summary

The vulnerability exists in the /api/session/import handler of Hermes WebUI prior to version 0.51.521. During session import, the handler validates that the imported session's workspace matches the currently active named profile. However, the Session object is constructed and persisted without explicitly setting the profile field, leaving it null. The application's profile authorization logic treats null profile values as equivalent to the default profile. This allows a default profile user to export an imported session, obtain its session identifier, and leverage that identifier to read file system objects from a named profile's workspace directory, circumventing intended profile-based access controls.

Business impact

This vulnerability breaks the multi-workspace isolation model that Hermes WebUI relies on to segregate user data and permissions. Depending on the sensitivity of files stored in named profiles, an attacker with default profile access could exfiltrate confidential information, source code, credentials, or other protected assets belonging to users or teams using isolated workspaces. In shared Hermes deployments, this significantly increases the blast radius of a compromised low-privilege account.

Affected systems

Hermes WebUI versions before 0.51.521 are affected. Organizations running Hermes WebUI should verify their installed version immediately to determine exposure.

Exploitability

Exploitation requires valid login credentials to the Hermes WebUI instance (PR:L), but no user interaction is required beyond normal API calls (UI:N). The attack is feasible over the network with low attack complexity. The vulnerability does not require any special configuration or race conditions, making it straightforward to exploit once an attacker has basic authenticated access. The CVSS 3.1 score of 6.5 (MEDIUM) reflects the need for authentication and the confidentiality-only impact.

Remediation

Upgrade Hermes WebUI to version 0.51.521 or later. The patched version ensures that the Session object's profile field is properly populated during the import process, preventing null profile assignments and enforcing correct workspace isolation during subsequent file access operations.

Patch guidance

Apply the upgrade to Hermes WebUI 0.51.521 or later at your earliest convenience. Verify the patch version in your deployment and confirm that session import operations now correctly assign profile context. Test that users on different profiles can no longer access each other's workspaces via imported session identifiers.

Detection guidance

Monitor Hermes WebUI API logs for /api/session/import requests from default profile users, followed by /api/session/export calls and subsequent file read operations against paths from named profile workspaces. Look for session identifiers persisted with null profile values in application databases. Audit existing imported sessions to identify any that lack a profile assignment and may represent prior exploitation. Network detection is difficult because the attack uses legitimate API endpoints; log-based detection and session validation are more effective.

Why prioritize this

Although the CVSS score is MEDIUM, this vulnerability directly breaks a security boundary—profile isolation. In shared or multi-tenant environments where Hermes WebUI enforces workspace separation as a primary security control, unauthorized cross-profile access to files represents a meaningful confidentiality breach. Prioritize this above other MEDIUM-severity issues in your queue, especially if your organization relies on profile isolation for data protection or compliance.

Risk score, explained

The CVSS 3.1 score of 6.5 reflects: (1) Network accessibility and low attack complexity favor the attacker; (2) authentication is required, reducing the threat pool; (3) only confidentiality is impacted—integrity and availability are unaffected; (4) the scope is unchanged (single security domain). The score does not account for context-specific factors such as how critical the data in named profiles is or how many users have default profile access in your environment.

Frequently asked questions