GHSA-89xv-2j6f-qhc8 CVE-2026-33252 GO-2026-4773
Cross-Site Tool Execution for HTTP Servers without Authorizatrion in github.com/modelcontextprotocol/go-sdk
- Severity
- 7.1 / 10
- Medium · CVSS 3.1
- Exploit chance (EPSS)
- 0.18%
- Chance of exploitation in the next 30 days. Higher than 7.67% of scored vulnerabilities.
- Known exploited
- No
- Not in CISA's catalog
- Weakness
- CWE-352 Cross-Site Request Forgery (CSRF)
- Fix
1.4.1- Upgrade github.com/modelcontextprotocol/go-sdk to this version or later
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 versions
Go
| Package | Vulnerable | Fixed in |
|---|---|---|
| github.com/modelcontextprotocol/go-sdk | <= 1.4.0 |
No fix yet |
| github.com/modelcontextprotocol/go-sdk | < 1.4.1 |
1.4.1 |
How to fix
Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.
github.com/modelcontextprotocol/go-sdk Go → 1.4.1
- go
go get github.com/modelcontextprotocol/go-sdk@v1.4.1 && go mod tidy
Severity breakdown
CVSS 3.1 7.1
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:L
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- None
- User interaction
- Required
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- High
- Availability
- Low
Weakness
CWE-352: Cross-Site Request Forgery (CSRF)
The web application does not, or cannot, sufficiently verify whether a request was intentionally provided by the user who sent the request, which could have originated from an unauthorized actor.
How to prevent it
- Architecture and Design: Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid [REF-1482]. For example, use anti-CSRF packages such as the OWASP CSRFGuard. [REF-330] Another example is the ESAPI Session Management control, which includes a component for CSRF. [REF-45]
- Implementation: Ensure that the application is free of cross-site scripting issues (CWE-79), because most CSRF defenses can be bypassed using attacker-controlled script.
- Architecture and Design: Generate a unique nonce for each form, place the nonce into the form, and verify the nonce upon receipt of the form. Be sure that the nonce is not predictable (CWE-330). [REF-332]
- Architecture and Design: Identify especially dangerous operations. When the user performs a dangerous operation, send a separate confirmation request to ensure that the user intended to perform that operation.
- Architecture and Design: Use the "double-submitted cookie" method as described by Felten and Zeller: When a user visits a site, the site should generate a pseudorandom value and set it as a cookie on the user's machine. The site should require every form submission to include this value as a form value and also as a cookie value. When a POST request is sent to the site, the request should only be considered valid if the form value and the cookie value are the same. Because of the same-origin policy, an attacker cannot read or modify the value stored in the cookie. To successfully submit a form on behalf of the user, the attacker would have to correctly guess the pseudorandom value. If the pseudorandom value is cryptographically strong, this will be prohibitively difficult. This technique requires Javascript, so it may not work for browsers that have Javascript disabled. [REF-331]
- Architecture and Design: Do not use the GET method for any request that triggers a state change.
- Implementation: Check the HTTP Referer header to see if the request originated from an expected page. This could break legitimate functionality, because users or proxies may have disabled sending the Referer for privacy reasons.
References
Advisories
Fixes and patches
Packages
Timeline
- Published
- Last updated by the source
- Latest EPSS score
Related advisories
| Advisory | Severity | Why it's related |
|---|---|---|
| GHSA-xw59-hvm2-8pj6 DNS Rebinding Protection Disabled by Default in Model Context Protocol Go SDK for Servers Running on Localhost | High | Also affects github.com/modelcontextprotocol/go-sdk |
| GHSA-q382-vc8q-7jhj Improper handling of null Unicode character when parsing JSON in github.com/modelcontextprotocol/go-sdk | High | Also affects github.com/modelcontextprotocol/go-sdk |
| GHSA-wvj2-96wp-fq3f MCP Go SDK Vulnerable to Improper Handling of Case Sensitivity | High | Also affects github.com/modelcontextprotocol/go-sdk |
| GHSA-2p8c-gr87-2676 Electron: SameSite cookie restrictions are not applied to windows opened from links | Medium | Same weakness, CWE-352 |
| GO-2026-6773 Nginx UI: Casdoor SSO callback uses a constant `state` parameter (login CSRF) | High | Same weakness, CWE-352 |
| GHSA-9ff2-p842-45wq Contao: Cross-site request forgery in custom backend actions | Low | Same weakness, CWE-352 |
| GHSA-33rr-wq23-g6gg Nginx-UI AuthRequired token cookie fallback enables CSRF against management APIs | High | Same weakness, CWE-352 |
| GHSA-pvph-5j39-v8qc PraisonAI: Origin-validation bypass (startswith prefix match) enables unauthenticated cross-site request forgery against the PraisonAI MCP HTTP server | High | Same weakness, CWE-352 |
Credits: aleister1102
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