CVE-2026-15311Public exploitNetwork attack vector

Cross-site scripting via unsanitized Matrix Markdown

Published Jul 9, 2026 · Updated Jul 10, 2026

Cross-site scripting in Hermes Agent 2026.5.29.0 through 2026.5.29.2 allows remote authenticated users to inject Matrix HTML. The Matrix adapter's _markdown_to_html function copies Python Markdown output into formatted_body without escaping raw HTML or filtering javascript, data, and vbscript URL schemes. Exploitation requires the Matrix extra and untrusted content to reach the outbound send path; script execution depends on a downstream client that inadequately sanitizes Matrix custom HTML.

CVSS severity3.5
Low
EPSS probability0.36%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Cross-site scripting in Hermes Agent 2026.5.29.0 through 2026.5.29.2 allows remote authenticated users to inject Matrix HTML. The Matrix adapter's _markdown_to_html function copies Python Markdown output into formatted_body without escaping raw HTML or filtering javascript, data, and vbscript URL schemes. Exploitation requires the Matrix extra and untrusted content to reach the outbound send path; script execution depends on a downstream client that inadequately sanitizes Matrix custom HTML.

The record

CVE
CVE-2026-15311
Published
Jul 9, 2026
Updated
Jul 10, 2026
Vendor
Nous Research
Product
Hermes Agent
Classifications
CWE-79, CWE-94, T1203
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Jul 9, 2026CVE publishedPublication date reported by the CVE source.
  2. Jul 10, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=2026.5.29.0
  2. Affected versionversion=2026.5.29.1
  3. Affected versionversion=2026.5.29.2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Nous Research · Hermes Agentversion=2026.5.29.0; version=2026.5.29.1; version=2026.5.29.2

Published CVSS scores

2.0VulDBCVSS: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
3.5VulDBCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:N/I:L/A:N
4.0VulDBAV:N/AC:L/Au:S/C:N/I:P/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
CWE-94Improper Control of Generation of Code ('Code Injection')
T1203Exploitation for Client Execution

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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