CVE-2026-27896
MCP Go SDK Vulnerable to Improper Handling of Case Sensitivity
Description
The Go MCP SDK used Go's standard encoding/json.Unmarshal for JSON-RPC and MCP protocol message parsing in versions prior to 1.3.1. Go's standard library performs case-insensitive matching of JSON keys to struct field tags — a field tagged json:"method" would also match "Method", "METHOD", etc. This violated the JSON-RPC 2.0 specification, which defines exact field names. A malicious MCP peer may have been able to send protocol messages with non-standard field casing that the SDK would silently accept. This had the potential for bypassing intermediary inspection and coss-implementation inconsistency. Go's standard JSON unmarshaling was replaced with a case-sensitive decoder in commit 7b8d81c. Users are advised to update to v1.3.1 to resolve this issue.
INFO
Published Date :
Feb. 26, 2026, 1:16 a.m.
Last Modified :
June 30, 2026, 3:17 a.m.
Remotely Exploit :
Yes !
Source :
[email protected]
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS | 134c704f-9b21-4f2e-91b3-4a467353bcc0 | |||||
| CVSS 3.1 | HIGH | [email protected] | ||||
| CVSS 3.1 | HIGH | 0b0ca135-0b70-47e7-9f44-1890c2a1c46c | ||||
| CVSS 4.0 | HIGH | [email protected] |
Solution
- Update the Go MCP SDK to version 1.3.1.
- Ensure JSON key matching is case-sensitive.
- Review MCP protocol message parsing.
Public PoC/Exploit Available at Github
CVE-2026-27896 has a 1 public
PoC/Exploit available at Github.
Go to the Public Exploits tab to see the list.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-27896.
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-27896 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-27896
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
The Project shares all information on MCP related CVE's published
mcp mcp-security mcp-cve
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-27896 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-27896 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
CVE Modified by 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
Jun. 30, 2026
Action Type Old Value New Value Added Affected [{'cpes': ['cpe:/a:redhat:migration_toolkit_virtualization:2'], 'vendor': 'Red Hat', 'product': 'Migration Toolkit for Virtualization', 'defaultStatus': 'affected'}, {'cpes': ['cpe:/a:redhat:openshift_lightspeed'], 'vendor': 'Red Hat', 'product': 'OpenShift Lightspeed', 'defaultStatus': 'affected'}, {'cpes': ['cpe:/a:redhat:serverless:1'], 'vendor': 'Red Hat', 'product': 'OpenShift Serverless', 'defaultStatus': 'affected'}, {'cpes': ['cpe:/a:redhat:openshift_ai'], 'vendor': 'Red Hat', 'product': 'Red Hat OpenShift AI (RHOAI)', 'defaultStatus': 'affected'}] Added CVSS V3.1 AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N Added CWE CWE-178 Added Reference https://access.redhat.com/security/cve/CVE-2026-27896 Added Reference https://bugzilla.redhat.com/show_bug.cgi?id=2442903 Added Reference https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-27896.json -
CVE Modified by [email protected]
Jun. 17, 2026
Action Type Old Value New Value Added Affected [{'vendor': 'modelcontextprotocol', 'product': 'go-sdk', 'versions': [{'status': 'affected', 'version': '< 1.3.1'}]}] -
CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Jun. 17, 2026
Action Type Old Value New Value Added SSVC {'id': 'CVE-2026-27896', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'none'}, {'automatable': 'yes'}, {'technicalImpact': 'partial'}], 'version': '2.0.3', 'timestamp': '2026-02-26T17:06:14.973622Z'} -
Initial Analysis by [email protected]
Apr. 14, 2026
Action Type Old Value New Value Added CVSS V3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N Added CPE Configuration OR *cpe:2.3:a:lfprojects:mcp_go_sdk:*:*:*:*:*:*:*:* versions up to (excluding) 1.3.1 Added Reference Type GitHub, Inc.: https://github.com/modelcontextprotocol/go-sdk/commit/7b8d81c264074404abdf5aa16e2cf0c2d9c64cc0 Types: Patch Added Reference Type GitHub, Inc.: https://github.com/modelcontextprotocol/go-sdk/security/advisories/GHSA-wvj2-96wp-fq3f Types: Patch, Vendor Advisory -
New CVE Received by [email protected]
Feb. 26, 2026
Action Type Old Value New Value Added Description The Go MCP SDK used Go's standard encoding/json.Unmarshal for JSON-RPC and MCP protocol message parsing in versions prior to 1.3.1. Go's standard library performs case-insensitive matching of JSON keys to struct field tags — a field tagged json:"method" would also match "Method", "METHOD", etc. This violated the JSON-RPC 2.0 specification, which defines exact field names. A malicious MCP peer may have been able to send protocol messages with non-standard field casing that the SDK would silently accept. This had the potential for bypassing intermediary inspection and coss-implementation inconsistency. Go's standard JSON unmarshaling was replaced with a case-sensitive decoder in commit 7b8d81c. Users are advised to update to v1.3.1 to resolve this issue. Added CVSS V4.0 AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:N/SC:H/SI:H/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 Added CWE CWE-436 Added CWE CWE-178 Added Reference https://github.com/modelcontextprotocol/go-sdk/commit/7b8d81c264074404abdf5aa16e2cf0c2d9c64cc0 Added Reference https://github.com/modelcontextprotocol/go-sdk/security/advisories/GHSA-wvj2-96wp-fq3f