Impact Analysis

The vulnerability can lead to denial of service for legitimate webhook events. Because the rate limit bucket is exhausted by invalid requests, valid webhook deliveries are dropped or delayed.

• Dropped legitimate webhook events
• Delayed bot workflows
• Degraded reliability for automated systems relying on these webhooks

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Executive Summary

CVE-2026-10224 is a logic flaw in the Feishu webhook handler of the Hermes Agent software. The vulnerability occurs because rate limiting is applied before verifying the signature and token of incoming webhook requests. This means that unauthenticated requests with invalid signatures still consume the same rate-limit bucket as legitimate traffic.

An attacker can exploit this by sending many malformed requests, which exhausts the rate limit and causes valid signed webhook deliveries to be rejected with HTTP 429 errors.

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Detection Guidance

This vulnerability can be detected by monitoring for repeated malformed webhook requests that cause legitimate signed webhook deliveries to be rejected with HTTP 429 errors.

Specifically, detection involves identifying unauthenticated requests with invalid signatures that consume the same rate-limit bucket as legitimate traffic.

Network or system administrators can look for an unusual number of HTTP 429 (Too Many Requests) responses from the Hermes Agent webhook endpoint, indicating rate limit exhaustion.

Commands to assist detection might include using tools like curl or wget to simulate malformed webhook requests and monitoring logs for HTTP 429 responses.

• Use curl to send a malformed webhook request: curl -X POST https://your-hermes-agent-endpoint/webhook -H "X-Signature: invalid" -d '{}'
• Check server logs for HTTP 429 responses indicating rate limit exhaustion.
• Use network monitoring tools (e.g., tcpdump, Wireshark) to capture and analyze traffic patterns for repeated invalid webhook requests.

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Mitigation Strategies

Immediate mitigation steps include updating the Hermes Agent package to a version later than v2026.4.30 where the vulnerability has been patched.

Until an update can be applied, consider implementing additional rate limiting or filtering at the network or application firewall level to block unauthenticated or malformed webhook requests.

Monitoring and alerting on HTTP 429 errors can help detect ongoing exploitation attempts and allow for timely response.

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Compliance Impact

The vulnerability causes resource consumption leading to denial of service for legitimate webhook events, which can degrade the reliability of automated systems. However, there is no direct information indicating an impact on data confidentiality, integrity, or privacy that would affect compliance with standards like GDPR or HIPAA.

Since the vulnerability does not involve unauthorized data access or leakage but rather affects availability, its compliance impact is limited to potential service disruption rather than violation of data protection regulations.

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