CVE-2026-34742
What it is
The Go MCP SDK used Go's standard encoding/json. Prior to version 1.4.0, the Model Context Protocol (MCP) Go SDK does not enable DNS rebinding protection by default for HTTP-based servers. When an HTTP-based MCP server is run on localhost without authentication with StreamableHTTPHandler or SSEHandler, a malicious website could exploit DNS rebinding to bypass same-origin policy restrictions and send requests to the local MCP server. This could allow an attacker to invoke tools or access resources exposed by the MCP server on behalf of the user in those limited circumstances. This issue has been patched in version 1.4.0.
At a glance
- Exploitability
- Can be exploited over the network without logging in, but needs a user to act. High risk of data exposure, data tampering.
- Exploit odds
- 0.5% chance of exploitation in the next 30 days (EPSS).
- Fix
- A patch, advisory or fixed version is referenced. Upgrade or apply it.
Timeline
- PublishedDisclosed publicly on CVE.org and NVD
- Last updatedMost recent change to the record
Why it ranks here
- Exploited in the wild: no, CISA does not list it.
- Exploit odds: 0.5% in the next 30 days (EPSS).
- Severity: 7.6 HIGH (CVSS).
- Fix: a patch or advisory is linked.
Details
- Published
- Last modified
- Exploit probability
- 0.5% · EPSS, next 30 days
- Weakness
- CWE-1188
- Record status
- Modified
Affected
- Lfprojects Mcp Go Sdk < 1.4.0
Attack profile CVSS 4.0 · 7.6
- Attack vector
- Network
- Complexity
- Low
- Attack requirements
- Present
- Privileges needed
- None
- User interaction
- Passive
- Confidentiality
- High
- Integrity
- High
- Availability
- None
Raw vector
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Is it in your code?
Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.
Read https://cve-list.com/agent/cve/CVE-2026-34742.md and follow it. Check whether this project is affected by CVE-2026-34742. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.
Fix and advisories
- https://github.com/modelcontextprotocol/go-sdk/commit/67bd3f2e2b53ce11a16db8d976cdb8ff1e986b6d
- https://github.com/modelcontextprotocol/go-sdk/pull/760
- https://github.com/modelcontextprotocol/go-sdk/releases/tag/v1.4.0
- https://github.com/modelcontextprotocol/go-sdk/security/advisories/GHSA-xw59-hvm2-8pj6
References
- https://github.com/modelcontextprotocol/go-sdk/commit/67bd3f2e2b53ce11a16db8d976cdb8ff1e986b6d
- https://github.com/modelcontextprotocol/go-sdk/pull/760
- https://github.com/modelcontextprotocol/go-sdk/releases/tag/v1.4.0
- https://github.com/modelcontextprotocol/go-sdk/security/advisories/GHSA-xw59-hvm2-8pj6
- https://access.redhat.com/errata/RHSA-2026:21772
- https://access.redhat.com/security/cve/CVE-2026-34742
- https://bugzilla.redhat.com/show_bug.cgi?id=2454608
- https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-34742.json