CVE-2026-81092 mark3labs CVE debrief

Who should care

Defenders responsible for mcp-go deployments, especially those listening on loopback addresses, should assess exposure and verify version 0.56.0 or later is in use. This includes operators, platform administrators, vulnerability management teams, and security teams who need to ensure that mcp-go instances are properly secured and monitored for potential DNS rebinding attacks.

Why it matters

CVE-2026-81092 allows an attacker to bypass Host header validation on loopback connections in mcp-go, potentially enabling DNS rebinding attacks. Defenders should prioritize verifying exposure and ensuring version 0.56.0 or later is in use.

• Verify mcp-go instances are running version 0.56.0 or later to prevent potential DNS rebinding attacks
• Assess exposure of mcp-go instances listening on loopback addresses to determine potential attack surface
• Implement compensating controls to detect and prevent DNS rebinding attacks

Technical summary

The mcp-go library did not validate the Host header on loopback connections, allowing an attacker to potentially bypass security restrictions. This issue was addressed in version 0.56.0. The vulnerability affects mcp-go instances listening on loopback addresses, and defenders should assess exposure and verify version 0.56.0 or later is in use. The CVE record and NVD entry provide details on the vulnerability, including its description and affected versions. However, the scope of affected deployments and potential impacts require further verification.

Defensive priority

Defenders should prioritize verifying exposure of mcp-go instances, especially those listening on loopback addresses, and ensure they are running version 0.56.0 or later.

Recommended defensive actions

• Verify mcp-go instances are running version 0.56.0 or later
• Assess exposure of mcp-go instances listening on loopback addresses
• Implement compensating controls to detect and prevent DNS rebinding attacks
• Review the supplied official advisory or CVE record to validate affected scope, severity, and vendor guidance
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up
• Plan vendor-supported updates or mitigations through normal change control where exposure is confirmed
• Track exceptions, retest remediated assets, and close the item only after evidence is documented

Evidence notes

The CVE record and NVD entry provide details on the vulnerability, including its description and affected versions. However, the scope of affected deployments and potential impacts require further verification.

Sources and 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.