{"dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": {"cveId": "CVE-2026-27896", "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa", "state": "PUBLISHED", "assignerShortName": "GitHub_M", "dateReserved": "2026-02-24T15:19:29.717Z", "datePublished": "2026-02-26T00:47:46.967Z", "dateUpdated": "2026-02-26T00:47:46.967Z"}, "containers": {"cna": {"title": "MCP Go SDK Vulnerable to Improper Handling of Case Sensitivity", "problemTypes": [{"descriptions": [{"cweId": "CWE-178", "lang": "en", "description": "CWE-178: Improper Handling of Case Sensitivity", "type": "CWE"}]}, {"descriptions": [{"cweId": "CWE-436", "lang": "en", "description": "CWE-436: Interpretation Conflict", "type": "CWE"}]}], "metrics": [{"cvssV4_0": {"attackVector": "NETWORK", "attackComplexity": "LOW", "attackRequirements": "PRESENT", "privilegesRequired": "NONE", "userInteraction": "NONE", "vulnConfidentialityImpact": "NONE", "vulnIntegrityImpact": "NONE", "vulnAvailabilityImpact": "NONE", "subConfidentialityImpact": "HIGH", "subIntegrityImpact": "HIGH", "subAvailabilityImpact": "NONE", "baseScore": 7, "baseSeverity": "HIGH", "vectorString": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:N/SC:H/SI:H/SA:N", "version": "4.0"}}], "references": [{"name": "https://github.com/modelcontextprotocol/go-sdk/security/advisories/GHSA-wvj2-96wp-fq3f", "tags": ["x_refsource_CONFIRM"], "url": "https://github.com/modelcontextprotocol/go-sdk/security/advisories/GHSA-wvj2-96wp-fq3f"}, {"name": "https://github.com/modelcontextprotocol/go-sdk/commit/7b8d81c264074404abdf5aa16e2cf0c2d9c64cc0", "tags": ["x_refsource_MISC"], "url": "https://github.com/modelcontextprotocol/go-sdk/commit/7b8d81c264074404abdf5aa16e2cf0c2d9c64cc0"}], "affected": [{"vendor": "modelcontextprotocol", "product": "go-sdk", "versions": [{"version": "< 1.3.1", "status": "affected"}]}], "providerMetadata": {"orgId": "a0819718-46f1-4df5-94e2-005712e83aaa", "shortName": "GitHub_M", "dateUpdated": "2026-02-26T00:47:46.967Z"}, "descriptions": [{"lang": "en", "value": "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 \u2014 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."}], "source": {"advisory": "GHSA-wvj2-96wp-fq3f", "discovery": "UNKNOWN"}}}}

{}

{"cveTags": [], "descriptions": [{"lang": "en", "value": "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 \u2014 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."}], "id": "CVE-2026-27896", "lastModified": "2026-02-26T01:16:25.630", "metrics": {"cvssMetricV40": [{"cvssData": {"Automatable": "NOT_DEFINED", "Recovery": "NOT_DEFINED", "Safety": "NOT_DEFINED", "attackComplexity": "LOW", "attackRequirements": "PRESENT", "attackVector": "NETWORK", "availabilityRequirement": "NOT_DEFINED", "baseScore": 7.0, "baseSeverity": "HIGH", "confidentialityRequirement": "NOT_DEFINED", "exploitMaturity": "NOT_DEFINED", "integrityRequirement": "NOT_DEFINED", "modifiedAttackComplexity": "NOT_DEFINED", "modifiedAttackRequirements": "NOT_DEFINED", "modifiedAttackVector": "NOT_DEFINED", "modifiedPrivilegesRequired": "NOT_DEFINED", "modifiedSubAvailabilityImpact": "NOT_DEFINED", "modifiedSubConfidentialityImpact": "NOT_DEFINED", "modifiedSubIntegrityImpact": "NOT_DEFINED", "modifiedUserInteraction": "NOT_DEFINED", "modifiedVulnAvailabilityImpact": "NOT_DEFINED", "modifiedVulnConfidentialityImpact": "NOT_DEFINED", "modifiedVulnIntegrityImpact": "NOT_DEFINED", "privilegesRequired": "NONE", "providerUrgency": "NOT_DEFINED", "subAvailabilityImpact": "NONE", "subConfidentialityImpact": "HIGH", "subIntegrityImpact": "HIGH", "userInteraction": "NONE", "valueDensity": "NOT_DEFINED", "vectorString": "CVSS:4.0/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", "version": "4.0", "vulnAvailabilityImpact": "NONE", "vulnConfidentialityImpact": "NONE", "vulnIntegrityImpact": "NONE", "vulnerabilityResponseEffort": "NOT_DEFINED"}, "source": "security-advisories@github.com", "type": "Secondary"}]}, "published": "2026-02-26T01:16:25.630", "references": [{"source": "security-advisories@github.com", "url": "https://github.com/modelcontextprotocol/go-sdk/commit/7b8d81c264074404abdf5aa16e2cf0c2d9c64cc0"}, {"source": "security-advisories@github.com", "url": "https://github.com/modelcontextprotocol/go-sdk/security/advisories/GHSA-wvj2-96wp-fq3f"}], "sourceIdentifier": "security-advisories@github.com", "vulnStatus": "Received", "weaknesses": [{"description": [{"lang": "en", "value": "CWE-178"}, {"lang": "en", "value": "CWE-436"}], "source": "security-advisories@github.com", "type": "Primary"}]}

{}

{}