CVE-2026-49957: Hermes WebUI Workspace Boundary Bypass (v0.51.296)

Technical summary

The vulnerability exists in the _remote_terminal_workspace_candidate() function, which resolves workspace paths for SSH and remote terminal profiles. The function contains a logic flaw where it returns early and accepts a workspace directory before the _is_blocked_workspace_path() validation guard executes. This allows authenticated users to configure remote terminal working directories pointing to protected system paths like /etc. The premature acceptance bypasses the path boundary check, enabling subsequent file-read helpers to access files outside the intended workspace isolation boundary. The root cause is an ordering issue in the security validation chain rather than a missing check entirely.

Business impact

Organizations using Hermes WebUI face a risk of unauthorized disclosure of sensitive system configuration files that should remain restricted. Authenticated users—whether internal staff, contractors, or compromised accounts—could potentially read /etc/passwd, configuration files, or other system metadata that could inform further attacks or reveal sensitive configuration details. This escalates the risk profile of any compromised user account on the system, as their effective permissions exceed what the application intended to grant.

Affected systems

Hermes WebUI versions prior to 0.51.296 are affected. No other vendors or products are identified in the vulnerability record. Organizations should identify all running instances of Hermes WebUI and determine their current version to assess exposure.

Exploitability

Exploitation requires valid authentication credentials—this is not an unauthenticated attack. The vulnerability scores HIGH (7.7 CVSS) despite the authentication requirement because the impact is severe (high confidentiality) and the attack complexity is low. Once authenticated, no complex setup or user interaction is needed; the attacker simply configures a remote terminal profile with a blocked path. The attack succeeds against the network boundary (AV:N), meaning remote exploitation is possible for any user with valid credentials, including those accessing the system over the network.

Remediation

Upgrade Hermes WebUI to version 0.51.296 or later. This version addresses the early-return logic flaw in the workspace resolution function. Organizations should prioritize this patch for instances exposed to untrusted or semi-trusted user populations. If an immediate upgrade is not feasible, restrict authentication credentials to only fully trusted users and monitor file access patterns for anomalous reads of system directories through the workspace API.

Patch guidance

Apply the update to Hermes WebUI 0.51.296 or later as soon as possible, particularly if the system is exposed to multiple user accounts or federated identity sources. Verify the patch by checking the running version in the WebUI administration panel or through the application logs. Test the patch in a non-production environment first to confirm no disruption to legitimate remote terminal workflows. The patch should restore proper validation order in the workspace resolution logic without requiring configuration changes.

Detection guidance

Monitor Hermes WebUI logs for remote terminal profile creation or modification attempts that reference system paths (e.g., /etc, /var, /sys). Look for file-read API calls that access paths outside the user's declared workspace root, particularly from authenticated sessions. Query application audit logs for workspace resolution failures or security guard bypasses if the logging is sufficiently detailed. Network-based detection is difficult since the attack uses legitimate WebUI endpoints; detection relies on understanding the application's intended behavior and identifying deviations. Alerting on configuration of remote terminal working directories that begin with / and are not user home directories may help identify suspicious activity.

Why prioritize this

This vulnerability merits prompt attention despite the authentication requirement because: (1) HIGH severity with confirmed confidentiality impact; (2) low attack complexity—no sophisticated exploitation steps required; (3) affects the workspace isolation model, which is a foundational security boundary; (4) not yet in the CISA KEV catalog, indicating less industry awareness and potentially lower patch adoption; (5) any organization with multi-user or federated access to Hermes WebUI faces meaningful risk. Prioritize patching instances in high-sensitivity environments first.

Risk score, explained

The CVSS 3.1 score of 7.7 reflects HIGH severity. The score captures: (1) Network exploitability (AV:N)—authenticated users can attack from the network; (2) Low attack complexity (AC:L)—no special conditions or user interaction required; (3) Low privilege requirement (PR:L)—any authenticated user can exploit this; (4) Scope change (S:C)—the impact extends beyond the vulnerable component to the broader system; (5) High confidentiality impact (C:H)—unauthorized file read access to system files; (6) No integrity or availability impact (I:N, A:N). The authentication requirement prevents a higher score, but the broad impact and ease of exploitation within the authenticated context justify the HIGH rating.

Frequently asked questions