What is the CVSS score of CVE-2026-9366?

CVE-2026-9366 has a CVSS 4.0 base score of 5.5 (Medium). CVSS vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:L/SC:N/SI:N/SA:N/E:P. EPSS exploitation probability: 0.0%.

Is there a public PoC exploit available for CVE-2026-9366?

Yes, a public proof-of-concept exploit is available for CVE-2026-9366. Prioritise patching immediately. EPSS: 0.0%.

How to fix or mitigate CVE-2026-9366?

Within 24 hours: Identify all systems running NousResearch hermes-agent up to version 2026.4.23 and isolate affected instances from untrusted networks. Within 7 days: Engage NousResearch for patch timeline confirmation; if no vendor patch is forthcoming, evaluate alternative agent libraries or implement network segmentation to restrict access to hermes-agent endpoints to trusted sources only. Within 30 days: Execute migration to a patched version once available, or complete transition to a vendor-supported alternative if NousResearch does not release a fix.

hermes-agent CVE-2026-9366

EUVD-2026-31580 MEDIUM

Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection') (CWE-74)

2026-05-24 VulDB

GHSA-pgp4-xr4j-h5cg

Code Injection Hermes Agent Nousresearch

5.5

CVSS 4.0 · Vendor: VulDB

View

Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata – not a confirmed exploit chain

Access

Send crafted request to hermes-agent
Delivery

Reach _scan_context_content function
Exploit

Inject malicious payload
Execution

Execute arbitrary code
Impact

Achieve partial system impact

Vulnerability Assessment

Weakness	CWE CWE-74 OWASP Top 10:2025 A05:2025 - Injection ASVS 5.0 V1 - Encoding and Sanitization Input neutralization, injection prevention
Exploitation Conditions	No special conditions - remote unauthenticated exploitation against default configurations of hermes-agent. The vulnerability requires only that the hermes-agent service is network-accessible and processes user input through the affected _scan_context_content function. No authentication, special configuration, or user interaction is required based on the CVSS vector PR:N/UI:N.
Impact	The CVSS 3.1 score of 7.3 reflects a high-severity vulnerability with network attack vector, low complexity, and no required privileges or user interaction. The CVSS E:P metric confirms proof-of-concept code exists, which aligns with the public exploit on GitHub. However, there's no CISA KEV listing indicating active exploitation in the wild. The combination of remote unauthenticated access and available exploit code makes this a priority for organizations using hermes-agent, though the limited impact ratings (C:L/I:L/A:L) suggest partial rather than complete system compromise. The vendor's lack of response (RL:X) increases risk as no official patch timeline exists.
Exploit ScenarioDerived	An attacker sends specially crafted input to a hermes-agent instance exposed to the network. The malicious payload reaches the _scan_context_content function in prompt_builder.py without proper sanitization, allowing the attacker to inject and execute arbitrary code within the application context. Public exploit code at https://gist.github.com/YLChen-007/581fd92de5548fbaacb2092e848a75cc demonstrates the attack methodology.

This Month Plan within 30 days. Why: MEDIUM severity (CVSS 4.0-6.9).

Patch available 0.0% exploitation probability (EPSS)

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AnalysisAIv1 – May 24, 2026

Code injection in NousResearch hermes-agent 2026.4.23 allows remote unauthenticated attackers to inject and execute arbitrary code through the _scan_context_content function in agent/prompt_builder.py. The vulnerability has publicly available exploit code and affects all versions up to 2026.4.23, with the vendor failing to respond to disclosure attempts.

RemediationAI

No vendor-released patch identified at time of analysis due to vendor non-response. Organizations should immediately review usage of the _scan_context_content function and implement input validation for any data passed to this function. Consider temporarily disabling or restricting access to functionality that uses prompt_builder.py until a patch is available. Monitor the VulDB references at https://vuldb.com/vuln/365329 for updates. As a compensating control, implement web application firewall rules to filter potentially malicious input patterns targeting this injection vulnerability, though this may impact legitimate functionality.

Affected VersionsENISA

hermes-agent 2026.4.23

Affected Packages

pypi hermes-agent fix: 0.15.0

Source: OSV (Open Source Vulnerabilities)

Affects your stack

Affects 1 package in pypi

Checking this CVE against your own stacks and servers is part of the Basic plan and up.

Technical ContextAI · show details

The vulnerability exists in the _scan_context_content function within the prompt_builder.py module of hermes-agent, a NousResearch product. The issue is classified as CWE-74 (Improper Neutralization of Special Elements in Output Used by a Downstream Component), indicating that user-controlled input is not properly sanitized before being used in a way that allows injection attacks. The CPE string indicates all versions of hermes-agent are affected.

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Exploit and PoC references, threat intelligence from 22 sources

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Severity by source

Vendor (VulDB) PRIMARY 5.5 MEDIUM

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:L/SC:N/SI:N/SA:N/E:P

Primary rating from Vendor (VulDB) · only source for this CVE.

CVSS VectorVendor: VulDB

Attack Vector

Network

Attack Complexity

Low

Attack Requirements

None

Privileges Required

None

User Interaction

None

Vulnerable system: Confidentiality

Low

Vulnerable system: Integrity

Low

Vulnerable system: Availability

Low

Subsequent system: Confidentiality

None

Subsequent system: Integrity

None

Subsequent system: Availability

None

Lifecycle Timeline

Severity Changed

May 26, 2026 - 19:52 NVD

HIGH MEDIUM

CVSS changed

May 26, 2026 - 19:52 NVD

7.3 (HIGH) 5.5 (MEDIUM)

DescriptionCVE.org

A vulnerability was found in NousResearch hermes-agent 2026.4.23. The impacted element is the function _scan_context_content of the file agent/prompt_builder.py. The manipulation results in injection. The attack may be performed from remote. The exploit has been made public and could be used. The vendor was contacted early about this disclosure but did not respond in any way.

Executive ViewAI

Why It Matters

NousResearch hermes-agent versions up to 2026.4.23 contain an unauthenticated remote code execution vulnerability in the context scanning function that allows attackers to execute arbitrary code on affected systems. This poses an immediate threat to any organization deploying this agent component, as publicly available exploit code exists and the vendor has not released a patch despite disclosure attempts.

Business Impact: Severe

Compensating Controls

No vendor-released patch identified at time of analysis. Interim mitigations: (1) Restrict network access to hermes-agent endpoints using firewall rules and IP allowlisting; (2) Disable or remove the _scan_context_content function if not operationally required; (3) Implement Web Application Firewall rules to detect code injection patterns in requests to agent/prompt_builder.py endpoints; (4) Run hermes-agent in a sandboxed environment with minimal system privileges and limited outbound network access; (5) Monitor for suspicious execution patterns or unexpected child processes spawned by the agent service.

Threat Intelligence Overview

EPSS Score

0.0%

Top 86% exploitable

Exploit

POC

Public exploit code exists

Data Quality

6 sources

Confidence: High

EUVD

NVD

CVE.org

EPSS

GitHub

VulDB

How this decision was reached

The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.

SignalValue

Severity MEDIUM

CISA KEV No

Public POC Yes

EPSS 0.0%

Patch available Yes

Active threat No

Deciding rule

MEDIUM severity (CVSS 4.0-6.9)

What every action level means

Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.

Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.

This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.

This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.

Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

SSVC AssessmentENISA

SSVC Decision· derived

Out-of-Cycle

Exploitation· derived

Poc

System Exposure· derived

Open

Automatable· derived

Yes

Human Impact

Very High

Priority Score

Low Medium High Critical

KEV: 0

EPSS: 0

CVSS: +28

PoC: +20

Weaponized: 0

Threat intel: 0

Gov advisory: 0

Attack Technique

Code Injection CRITICAL

Code injection occurs when an application accepts user input and passes it directly into a language interpreter or evaluator without proper sanitization.