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hermes-agent CVE-2026-15311

| EUVDEUVD-2026-42764 LOW
Cross-site Scripting (XSS) (CWE-79)
2026-07-09 VulDB GHSA-93m6-38r7-vqmh
XSS Hermes Agent
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

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
Attack Vector
Network
Attack Complexity
Low
Privileges Required
Low
User Interaction
P
Scope
X

Lifecycle Timeline

3
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. …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

Access
Authenticate with low-privilege account
Delivery
Craft markdown with embedded XSS payload
Exploit
Send message via Matrix Adapter
Execution
_markdown_to_html renders unsanitized HTML
Persist
Victim views message in client
Impact
Injected script executes in victim's browser
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Vulnerability AssessmentAI

Exploitation Exploitation requires: (1) the attacker holds a valid authenticated low-privilege account on the targeted hermes-agent instance (PR:L - unauthenticated exploitation is not supported by the CVSS vector); (2) the hermes-agent deployment has the Matrix Adapter integration enabled, since the vulnerable function exists solely in gateway/platforms/matrix.py and is not reachable through other platform adapters; (3) a victim user must passively view the attacker-crafted message in their Matrix client (UI:P). … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment The CVSS 4.0 score of 2.0 (AV:N/AC:L/AT:N/PR:L/UI:P/VC:N/VI:L/VA:N) accurately characterizes this as low severity. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario An authenticated user on a hermes-agent instance with the Matrix Adapter enabled crafts a markdown message embedding a malicious payload - for example, an image tag with an onerror handler or a hyperlink using a javascript: URI - and sends it to a shared Matrix room or direct channel. The _markdown_to_html function renders the message without sanitization, embedding the script in the HTML output. …
Remediation 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. … Detailed patch versions, workarounds, and compensating controls in full report.
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CVE-2026-15311 vulnerability details – vuln.today
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