CVE-2026-27896

{"id": "CVE-2026-27896", "cveTags": [], "metrics": {"cvssMetricV31": [{"type": "Primary", "source": "nvd@nist.gov", "cvssData": {"scope": "UNCHANGED", "version": "3.1", "baseScore": 7.5, "attackVector": "NETWORK", "baseSeverity": "HIGH", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N", "integrityImpact": "HIGH", "userInteraction": "NONE", "attackComplexity": "LOW", "availabilityImpact": "NONE", "privilegesRequired": "NONE", "confidentialityImpact": "NONE"}, "impactScore": 3.6, "exploitabilityScore": 3.9}], "cvssMetricV40": [{"type": "Secondary", "source": "security-advisories@github.com", "cvssData": {"Safety": "NOT_DEFINED", "version": "4.0", "Recovery": "NOT_DEFINED", "baseScore": 7.0, "Automatable": "NOT_DEFINED", "attackVector": "NETWORK", "baseSeverity": "HIGH", "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", "exploitMaturity": "NOT_DEFINED", "providerUrgency": "NOT_DEFINED", "userInteraction": "NONE", "attackComplexity": "LOW", "attackRequirements": "PRESENT", "privilegesRequired": "NONE", "subIntegrityImpact": "HIGH", "vulnIntegrityImpact": "NONE", "integrityRequirement": "NOT_DEFINED", "modifiedAttackVector": "NOT_DEFINED", "subAvailabilityImpact": "NONE", "vulnAvailabilityImpact": "NONE", "availabilityRequirement": "NOT_DEFINED", "modifiedUserInteraction": "NOT_DEFINED", "modifiedAttackComplexity": "NOT_DEFINED", "subConfidentialityImpact": "HIGH", "vulnConfidentialityImpact": "NONE", "confidentialityRequirement": "NOT_DEFINED", "modifiedAttackRequirements": "NOT_DEFINED", "modifiedPrivilegesRequired": "NOT_DEFINED", "modifiedSubIntegrityImpact": "NOT_DEFINED", "modifiedVulnIntegrityImpact": "NOT_DEFINED", "vulnerabilityResponseEffort": "NOT_DEFINED", "modifiedSubAvailabilityImpact": "NOT_DEFINED", "modifiedVulnAvailabilityImpact": "NOT_DEFINED", "modifiedSubConfidentialityImpact": "NOT_DEFINED", "modifiedVulnConfidentialityImpact": "NOT_DEFINED"}}]}, "published": "2026-02-26T01:16:25.630", "references": [{"url": "https://github.com/modelcontextprotocol/go-sdk/commit/7b8d81c264074404abdf5aa16e2cf0c2d9c64cc0", "tags": ["Patch"], "source": "security-advisories@github.com"}, {"url": "https://github.com/modelcontextprotocol/go-sdk/security/advisories/GHSA-wvj2-96wp-fq3f", "tags": ["Patch", "Vendor Advisory"], "source": "security-advisories@github.com"}], "vulnStatus": "Analyzed", "weaknesses": [{"type": "Primary", "source": "security-advisories@github.com", "description": [{"lang": "en", "value": "CWE-178"}, {"lang": "en", "value": "CWE-436"}]}], "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."}, {"lang": "es", "value": "El SDK de Go MCP utilizaba la funci\u00f3n est\u00e1ndar `encoding/json.Unmarshal` de Go para el an\u00e1lisis de mensajes del protocolo JSON-RPC y MCP en versiones anteriores a la 1.3.1. La biblioteca est\u00e1ndar de Go realiza una coincidencia que no distingue entre may\u00fasculas y min\u00fasculas de las claves JSON con las etiquetas de campo de las estructuras \u2014 un campo etiquetado como json:'method' tambi\u00e9n coincidir\u00eda con 'Method', 'METHOD', etc. Esto violaba la especificaci\u00f3n JSON-RPC 2.0, que define nombres de campo exactos. Un par MCP malicioso podr\u00eda haber sido capaz de enviar mensajes de protocolo con un uso de may\u00fasculas y min\u00fasculas no est\u00e1ndar en los campos que el SDK aceptar\u00eda silenciosamente. Esto ten\u00eda el potencial de eludir la inspecci\u00f3n intermedia y la inconsistencia entre implementaciones. El desenmascaramiento JSON est\u00e1ndar de Go fue reemplazado por un decodificador que distingue entre may\u00fasculas y min\u00fasculas en el commit 7b8d81c. Se aconseja a los usuarios actualizar a la versi\u00f3n 1.3.1 para resolver este problema."}], "lastModified": "2026-04-14T00:40:00.510", "configurations": [{"nodes": [{"negate": false, "cpeMatch": [{"criteria": "cpe:2.3:a:lfprojects:mcp_go_sdk:*:*:*:*:*:*:*:*", "vulnerable": true, "matchCriteriaId": "F490537C-6089-4989-A1B4-4072EADBA4DF", "versionEndExcluding": "1.3.1"}], "operator": "OR"}]}], "sourceIdentifier": "security-advisories@github.com"}