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PatchSiren cyber security CVE debrief

CVE-2026-53869 NousResearch CVE debrief

CVE-2026-53869 is a high-severity DNS rebinding vulnerability in Hermes Agent before 0.16.0. The vulnerability allows remote attackers to bypass Host and Origin validation via WebSocket endpoints. Specifically, the FastAPI HTTP middleware does not execute for WebSocket upgrade requests on /api/pty, /api/ws, /api/pub, and /api/events endpoints. This enables attackers to exploit DNS rebinding and inject malicious commands or read terminal output. The vulnerability has a CVSS score of 8.7 and is considered HIGH severity. Organizations using Hermes Agent should take immediate action to mitigate this vulnerability.

Vendor
NousResearch
Product
hermes-agent
CVSS
HIGH 8.7
CISA KEV
Not listed in stored evidence
Original CVE published
2026-06-17
Original CVE updated
2026-06-18
Advisory published
2026-06-17
Advisory updated
2026-06-18

Who should care

Organizations using Hermes Agent before version 0.16.0 should prioritize patching this vulnerability to prevent potential attacks. This includes teams responsible for maintaining and securing infrastructure that utilizes Hermes Agent.

Technical summary

The vulnerability exists in the WebSocket endpoints of Hermes Agent, specifically on /api/pty, /api/ws, /api/pub, and /api/events. The FastAPI HTTP middleware does not execute for WebSocket upgrade requests on these endpoints, allowing attackers to bypass Host and Origin validation. This can be exploited through DNS rebinding attacks, enabling malicious command injection or terminal output reading.

Defensive priority

high

Recommended defensive actions

  • Upgrade Hermes Agent to version 0.16.0 or later
  • Implement additional security measures to monitor and restrict WebSocket traffic
  • Conduct regular vulnerability assessments and penetration testing
  • Ensure proper configuration and hardening of FastAPI HTTP middleware
  • Monitor for suspicious activity and implement incident response plans

Evidence notes

The information provided is based on data from the National Vulnerability Database (NVD) and other reliable sources. The vulnerability details and CVSS score are subject to change as new information becomes available.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-53869 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-53869

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

  • CVE-2026-53869 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-53869

    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.