CVE-2026-71963 in Hermes Agent
Summary
by MITRE • 09/03/2026
Hermes Agent 0.18.2 through 0.21.0, fixed in commit f6234d0, contains a remote code execution vulnerability that allows attackers to execute arbitrary OS commands by supplying a malicious repository with a crafted .git/config that sets core.fsmonitor to an attacker-controlled command. When a user opens the malicious repository and sends any message, the agent triggers a git status index refresh which executes the injected command in the user's process context, exposing the full environment including configured provider API keys.
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Analysis
by VulDB Data Team • 09/03/2026
The vulnerability identified in Hermes Agent versions 0.18.2 through 0.21.0 represents a critical remote code execution flaw rooted in improper handling of Git configuration files within automated agent workflows. This specific issue arises from the application's reliance on standard Git operations to maintain repository state, specifically during index refreshes triggered by user interactions such as sending messages. The core technical deficiency lies in the interpretation of the core.fsmonitor setting within a .git/config file located inside an opened repository. By default, this configuration option is intended for filesystem monitoring daemons that assist Git in tracking changes efficiently. However, when Hermes Agent processes a maliciously crafted repository where this value has been overwritten with arbitrary shell commands rather than a valid executable path or script name, the agent inadvertently executes these commands as part of its routine status checks. This behavior effectively turns any repository opened by the user into a vector for code execution, bypassing traditional sandboxing expectations since the command runs within the same process context and privilege level as the Hermes Agent itself.
From an operational perspective, this vulnerability allows attackers to achieve arbitrary OS command execution with significant consequences beyond simple script running. Because the malicious commands are executed in the context of the user's active session, they inherit all associated environment variables and access permissions. This exposure is particularly severe because modern development agents often have access to sensitive credentials stored in environment configurations, such as API keys for cloud providers, database connections, or authentication tokens for third-party services. An attacker leveraging this flaw can exfiltrate these secrets, potentially leading to broader compromise of the user's infrastructure and data integrity. The attack vector is relatively straightforward yet highly effective: an adversary simply needs to distribute a repository containing the crafted .git/config file through any channel where users are likely to open or clone repositories for review or collaboration within the Hermes Agent environment.
This vulnerability aligns closely with CWE-78, which describes Improper Neutralization of Special Elements used in an OS Command, commonly known as OS Command Injection. The root cause is a failure to validate or sanitize input derived from external sources, specifically configuration files that are not strictly controlled by the application but rather by third-party repository owners. Furthermore, this attack pattern maps directly to MITRE ATT&CK technique T1059.004, which covers command and scripting interpretation via Unix Shell commands. The exploitation chain involves initial access through a trusted-looking artifact (the git repository), followed by privilege escalation in terms of scope rather than user level, as the agent already runs with the user's permissions. The impact is compounded by the fact that Git operations are often considered safe or low-risk, leading to insufficient scrutiny of configuration files during automated processing steps like status updates and index refreshes.
Mitigation strategies must focus on both immediate patching and long-term architectural changes. Users should immediately upgrade Hermes Agent to version 0.21.1 or later, where this issue has been addressed in commit f6234d0. The fix likely involves strict validation of the core.fsmonitor value to ensure it points only to allowed executables or is disabled entirely during automated operations that do not require filesystem monitoring. Additionally, developers should implement allowlisting mechanisms for Git configuration keys processed by the agent, ensuring that only expected parameters are interpreted and others are ignored or flagged as errors. Security teams should also audit existing repositories in use within their organizations for signs of tampered .git/config files and enforce policies that restrict the automatic execution of commands derived from repository metadata. Regular security training regarding the risks of opening untrusted codebases, even those appearing benign, remains essential to complement technical controls against such supply chain attacks.