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CVE-2026-15311 NousResearch CVE debrief

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. Users of NousResearch hermes-agent up to 2026.5.29.2 should assess the risk of cross site scripting and apply patches or mitigations as available.

Vendor
NousResearch
Product
hermes-agent
CVSS
LOW 2
CISA KEV
Not listed in stored evidence
Original CVE published
2026-07-10
Original CVE updated
2026-07-10
Advisory published
2026-07-10
Advisory updated
2026-07-10

Who should care

Users of NousResearch hermes-agent up to 2026.5.29.2 should assess the risk of cross site scripting and apply patches or mitigations as available. The vulnerability exists in the MatrixAdapter._markdown_to_html function of the gateway/platforms/matrix.py file in the Matrix Adapter component of NousResearch hermes-agent up to 2026.5.29.2.

Technical summary

The vulnerability exists in the MatrixAdapter._markdown_to_html function of the gateway/platforms/matrix.py file in the Matrix Adapter component of NousResearch hermes-agent up to 2026.5.29.2. This function is vulnerable to cross site scripting attacks when processing markdown input. The vulnerability has a CVSS score of 2 and a CVSS severity of LOW. Users of NousResearch hermes-agent up to 2026.5.29.2 should assess the risk of cross site scripting and apply patches or mitigations as available.

Defensive priority

Apply patches or mitigations for cross site scripting in NousResearch hermes-agent up to 2026.5.29.2. Implement input validation and output encoding for markdown processing. Monitor for and restrict exploitation attempts against the Matrix Adapter component.

Recommended defensive actions

  • Apply available patches for NousResearch hermes-agent up to 2026.5.29.2
  • Implement input validation and output encoding for markdown processing
  • Monitor for and restrict exploitation attempts against the Matrix Adapter component
  • Review compensating controls for exposed systems while remediation is scheduled and verified
  • Check relevant monitoring, detection, and logs for exposed assets that need extra review
  • Track exceptions, retest remediated assets, and close the item only after evidence is documented
  • Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up

Evidence notes

The CVE record was published on 2026-07-10T00:16:32.853Z and was last modified on 2026-07-10T15:43:30.330Z. The NVD entry is currently Deferred. The vulnerability exists in the MatrixAdapter._markdown_to_html function of the gateway/platforms/matrix.py file in the Matrix Adapter component of NousResearch hermes-agent up to 2026.5.29.2. This function is vulnerable to cross site scripting attacks when processing markdown input. Users of NousResearch hermes-agent up to 2026.5.29.2 should assess the risk of cross site scripting and apply patches or mitigations as available. The attack can be executed remotely.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-15311 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-15311

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2026-15311 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-15311

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.