Description

A flaw has been found in NousResearch hermes-agent 0.18.0. Affected by this issue is the function _sess_nowait of the file s71.py of the component Session Management. This manipulation of the argument session_id causes authorization bypass. The attack can be initiated remotely. The vendor was contacted early about this disclosure but did not respond in any way.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "7.3",
  "pubDate": "2026-09-03T13:06:21.250Z",
  "pubdate": "2026-09-03T13:06:21.250Z",
  "executiveSummary": "A critical security vulnerability has been identified in the Session Management component of NousResearch hermes-agent version 0.18.0.\nThe flaw stems from improper handling of the session_id argument within the _sess_nowait function located in s71.py, which permits an authorization bypass.\nThis vulnerability allows remote, unauthenticated attackers to manipulate session identifiers, potentially gaining unauthorized access to privileged sessions or administrative functionality.\nThe inability of the system to correctly validate or sanitize user-supplied session tokens presents a significant security risk, as it effectively nullifies access controls.\nGiven the remote exploitability of this vulnerability, the impact on the integrity and confidentiality of the Hermes-agent ecosystem is high.\nAs the vendor has remained unresponsive to disclosure attempts, the risk remains unmitigated in the affected software version.",
  "technicalDetails": "The vulnerability resides within the _sess_nowait function in s71.py, which acts as a critical entry point for session state management in hermes-agent 0.18.0.\nThe root cause of the flaw is an inadequate validation mechanism for the session_id parameter passed to this function. Instead of verifying the session against a secure, cryptographically signed token store or an encrypted server-side session map, the application trusts the user-supplied input implicitly.\nThe exploitation flow begins when a remote attacker crafts a malicious request containing a manipulated session_id. By submitting a crafted identifier—often involving predictable patterns or injection sequences—the attacker can trick the _sess_nowait function into associating the current connection with an existing, active, or administrative session context.\nBecause the function fails to perform a secondary check against established security tokens or internal session integrity markers, the logic assumes that the provided session_id is authentic if it meets basic format requirements.\nOnce the _sess_nowait function accepts the unauthorized session_id, the application grants the attacker the associated privileges linked to that session context.\nThis results in a total bypass of the authorization layer, allowing the attacker to perform actions that should be restricted to authenticated or privileged users.\nThere are no specific requirements for prior authentication; the attack is performed remotely and is initiated by providing the malicious session identifier during the initial connection or request handshake.\nThe post-exploitation impact is severe, potentially allowing for unauthorized command execution, sensitive data exfiltration, or the modification of application settings depending on the scope of the hijacked session's privileges.\nThe vulnerability exists entirely within the handling of session state logic in the s71.py file, which lacks robust defensive programming practices to prevent session hijacking or unauthorized session binding via input manipulation."
}