Is there a public PoC exploit available for CVE-2026-15311?

Yes, a public proof-of-concept exploit is available for CVE-2026-15311. Prioritise patching immediately. EPSS: 0.2%.

Is there a patch available for CVE-2026-15311?

Yes, a patch is available for CVE-2026-15311. Update the affected software to the latest version immediately.

hermes-agent CVE-2026-15311

Q: What is the CVSS score of CVE-2026-15311?

CVE-2026-15311 has a CVSS 4.0 base score of 2.0 (Low). CVSS vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:P/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X. EPSS exploitation probability: 0.2%.

EUVD-2026-42764 LOW

Cross-site Scripting (XSS) (CWE-79)

2026-07-09 VulDB

GHSA-93m6-38r7-vqmh

XSS Hermes Agent Nousresearch

2.0

CVSS 4.0 · Vendor: VulDB

Severity by source

Vendor (VulDB) PRIMARY

2.0 MEDIUM

CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:P/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

vuln.today AI

5.4 MEDIUM

Network-delivered XSS via Matrix messages requires PR:L (authenticated sender) and UI:R (victim must view); scope changes to victim browser session with low C/I impact.

3.1 AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N

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

Primary rating from Vendor (VulDB).

CVSS VectorVendor: VulDB

Attack Vector

Network

Attack Complexity

Low

Privileges Required

Low

User Interaction

Scope

Lifecycle Timeline

Analysis Generated

Jul 10, 2026 - 00:34 vuln.today

Severity Changed

Jul 10, 2026 - 00:22 NVD

MEDIUM LOW

CVSS changed

Jul 10, 2026 - 00:22 NVD

5.1 (MEDIUM) 2.0 (LOW)

DescriptionCVE.org

A vulnerability was identified in NousResearch hermes-agent up to 2026.5.29.2. Affected by this issue is the function MatrixAdapter._markdown_to_html of the file gateway/platforms/matrix.py of the component Matrix Adapter. Such manipulation leads to cross site scripting. The attack can be executed remotely. The exploit is publicly available and might be used. The pull request to fix this issue awaits acceptance.

AnalysisAI

Cross-site scripting in NousResearch hermes-agent (all versions through 2026.5.29.2) stems from unsanitized markdown-to-HTML conversion in the Matrix Adapter component, allowing an authenticated remote attacker to inject malicious scripts into Matrix platform messages. When a victim views the crafted content, the injected script executes in their browser context. Publicly available exploit code exists (GitHub issue #42667), though no public exploit identified at time of analysis maps to confirmed active exploitation - the CVSS 4.0 score of 2.0 reflects the low severity, limited scope, and required victim interaction.

Technical ContextAI

The root cause is CWE-79 (Improper Neutralization of Input During Web Page Generation - Cross-site Scripting) in the function MatrixAdapter._markdown_to_html within gateway/platforms/matrix.py. This component bridges hermes-agent - an AI agent orchestration framework by NousResearch - to the Matrix open federated messaging protocol. The function processes user-supplied markdown input and renders it to HTML without adequately neutralizing embedded HTML tags or JavaScript event handlers, meaning attacker-controlled content passes through into the final HTML output delivered to other clients. The affected CPE is cpe:2.3:a:nousresearch:hermes-agent:*:*:*:*:*:*:*:*, covering all releases up to 2026.5.29.2. Only deployments with the Matrix Adapter integration active are in scope.

RemediationAI

No official patched release has been confirmed - the upstream fix is pending review as pull request #42759 at https://github.com/NousResearch/hermes-agent/pull/42759. Organizations needing immediate mitigation can manually apply the changes from that PR, accepting the risk that unreviewed code may introduce instability. The most effective compensating control is to disable or remove the Matrix Adapter integration entirely if Matrix connectivity is not required, which eliminates the vulnerable code path with no functional side effect for non-Matrix deployments. If Matrix integration must remain active, restrict the ability to send markdown-formatted content to trusted, high-privilege accounts only, increasing the effective privilege requirement beyond PR:L. Monitor the GitHub repository at https://github.com/NousResearch/hermes-agent/ and the VulDB advisory at https://vuldb.com/vuln/377247 for an official patched release incorporating PR #42759.