CVE-2026-27896: The Go MCP SDK used Go's standard encoding/json.Unmarshal for JSON-RPC and MCP protocol message parsing in ver

Q: How do I fix CVE-2026-27896?

mcp go sdk: upgrade to 1.3.1. Exact commands for each OS are on this page.

Q: Is CVE-2026-27896 being exploited?

CVE-2026-27896 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2026-27896 affect?

CVE-2026-27896 affects mcp go sdk. Severity is high (CVSS 7.5). 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

Q: How urgent is CVE-2026-27896?

Priority 37/100. High severity; Remotely exploitable, no login, no user action

Routine

HIGH 7.5REMOTEUPGRADE

CVE-2026-27896 is a high-severity flaw (CVSS 7.5) affecting mcp go sdk. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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-

Why this priority

High severity
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.3% (top 78%)
CISA exploited list	No
Weakness	CWE-178, CWE-436
Published	2026-02-26
Last modified	2026-07-15

Publisher (CNA): GitHub, Inc. · Vendor: lfprojects

Last updated 2026-07-15 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-02-26 01:16 UTCPublished CVE record published
2026-07-15 02:19 UTCUpdated Record last modified

lfprojects mcp go sdk UPGRADE

Affected: < 1.3.1

Fixed in: 1.3.1

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy mcp-go-sdk || rpm -q mcp-go-sdk || mcp-go-sdk --version

2. UPGRADE to 1.3.1 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade mcp-go-sdk

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade mcp-go-sdk

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-27896?

mcp go sdk: upgrade to 1.3.1. Exact commands for each OS are on this page.

Is CVE-2026-27896 being exploited?

CVE-2026-27896 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-27896 affect?

CVE-2026-27896 affects mcp go sdk. Severity is high (CVSS 7.5). 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

How urgent is CVE-2026-27896?

Priority 37/100. High severity; Remotely exploitable, no login, no user action

Related CVEs

CVE-2026-34742 HIGH 8.1 UPGRADE The Go MCP SDK used Go's standard encoding/json
CVE-2026-33252 HIGH 7.1 UPGRADE The Go MCP SDK used Go's standard encoding/json

References

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