CVE-2026-33252 is a high-severity (CVSS 7.1) Cross-Site Request Forgery (CSRF) vulnerability in github.com/modelcontextprotocol/go-sdk. A fix is available for github.com/modelcontextprotocol/go-sdk — see the affected versions and patch details below.
MCP Go SDK Allows Cross-Site Tool Execution for HTTP Servers without Authorizatrion
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-33252.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
github.com/modelcontextprotocol/go-sdkReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.
Description
The Go SDK's Streamable HTTP transport accepted browser-generated cross-site POST requests without validating the Origin header and without requiring Content-Type: application/json. In deployments without Authorization, especially stateless or sessionless configurations, this allows an arbitrary website to send MCP requests to a local server and potentially trigger tool execution.
Impact:
A malicious website may have been able to send cross-site POST requests with Content-Type: text/plain, which due to CORS-safelisted properties would reach the MCP message handling without any CORS preflight barrier.
Fix:
The SDK was modified to perform Content-Type header validation for POST requests and introduced a configurable protection for verifying the origin of the request in commit a433a83. Users are advised to update to v1.4.1 to use this additional protection.
Note: v1.4.1 requires Go 1.25 or later.
Credits:
Thank you to Lê Minh Quân for reporting the issue.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/modelcontextprotocol/go-sdk | all versions | 1.4.1go get github.com/modelcontextprotocol/go-sdk@v1.4.1 |
Affected Products
mcp go sdklfprojectsDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/modelcontextprotocol/go-sdk, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/modelcontextprotocol/go-sdk to 1.4.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-33252 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
To mitigate this vulnerability, ensure that deployments utilizing the Go MCP SDK are configured with proper authorization mechanisms. This prevents unauthorized cross-site requests from triggering tool execution. Additionally, restrict network access to the local server running the SDK to trusted sources only, using firewall rules to limit exposure.Source: Red Hat security advisory for CVE-2026-33252 (CC BY 4.0)
| Product | Fixed in | Advisory |
|---|---|---|
| Red Hat OpenShift Dev Spaces 3.28 | devspaces/udi-rhel9:1779829736 | RHSA-2026:21772 |
Frequently Asked Questions
Is CVE-2026-33252 in your dependencies?
Find it across Go, including transitive dependencies.