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CVE Record

CVE-2026-34742: Model Context Protocol Go SDK: DNS Rebinding Protection Disabled by Default for Servers Running on Localhost

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.

HighCVSS 8Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

This issue affects Go applications using the Model Context Protocol Go SDK before 1.4.0. If a local, unauthenticated HTTP MCP server uses affected handlers, a malicious website visited by the user could reach that local service and misuse tools or resources it exposes.

Executive priority

Treat as high priority where MCP servers run locally and expose sensitive automation or data. Patch quickly, but prioritize confirmed unauthenticated localhost HTTP deployments over unaffected SDK usage.

Technical view

Before v1.4.0, the MCP Go SDK did not enable DNS rebinding protection by default for HTTP-based localhost servers using StreamableHTTPHandler or SSEHandler without authentication. The CVSS vector requires user interaction and high attack complexity, but allows high confidentiality and integrity impact.

Likely exposure

Exposure is limited to deployments using modelcontextprotocol/go-sdk versions before 1.4.0, running HTTP-based MCP servers on localhost without authentication through StreamableHTTPHandler or SSEHandler.

Exploitation context

The source bundle does not cite active exploitation or KEV listing. Exploitation requires a user to visit a malicious website, and depends on the local MCP server exposing useful tools or resources without authentication.

Researcher notes

Key constraints are localhost HTTP server, no authentication, affected handlers, and go-sdk below 1.4.0. Evidence supports a DNS rebinding class issue, not remote unauthenticated internet exploitation.

Mitigation direction

  • Upgrade modelcontextprotocol/go-sdk to version 1.4.0 or later.
  • Enable authentication for local HTTP-based MCP servers.
  • Review vendor advisory and release notes for current guidance.
  • Avoid exposing sensitive tools or resources through unauthenticated localhost MCP servers.

Validation and detection

  • Inventory applications importing modelcontextprotocol/go-sdk.
  • Confirm deployed go-sdk versions are 1.4.0 or later.
  • Identify localhost MCP servers using StreamableHTTPHandler or SSEHandler.
  • Check whether those servers require authentication.
  • Review exposed MCP tools and resources for sensitive actions or data.
Prepared
Confidence
high
Sources
8

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

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cwe · low confidence lookup

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cve · low confidence lookup

CVE-2026-34742 mapping review

Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.

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Vulnerability profileCVE Program record
Severity
High
CVSS
8 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:H/A:N

Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

2CVSS vectors
5Timeline events
2ADP providers
9Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: noneAutomatable: noTechnical Impact: total

CVSS vector scores

2 official scores

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
8CVSS 3.1HighCVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:H/A:N1.65.8redhat-SADP
7.6CVSS 4.0HighCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N——GitHub_M

Vulnerability scoring details

Base CVSS 4.0 score

7.6High
CVSS 4.0 vector shape for CVE-2026-34742Attack VectorAttack ComplexityAttack RequirementsPrivileges RequiredUser InteractionVS ConfidentialityVS IntegrityVS AvailabilitySS ConfidentialitySS IntegritySS Availability

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

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Attack Requirements
NonePresent
Privileges Required
NoneLowHigh
User Interaction
NonePassiveActive
VS Confidentiality
HighLowNone
VS Integrity
HighLowNone
VS Availability
HighLowNone
SS Confidentiality
HighLowNone
SS Integrity
HighLowNone
SS Availability
HighLowNone

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. ADP timelineredhat-SADP

    Made public.

  3. CVE publishedCVE Program

    The CVE record was published.

  4. ADP timelineredhat-SADP

    Reported to Red Hat.

  5. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

ADP provider summaries

CISA-ADPCISA ADP Vulnrichment
other:ssvc
redhat-SADPgithub.com/modelcontextprotocol/go-sdk: Model Context Protocol (MCP) Go SDK: DNS rebinding vulnerability allows unauthorized access
other:Red Hat severity ratingcvssV3_1
  • 2026-04-02T19:06:39.830Z: Reported to Red Hat.
  • 2026-04-02T18:32:34.781Z: Made public.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
modelcontextprotocolgo-sdk< 1.4.0Listed
Weakness

CWE details

CWE-1188

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.

CWE-1188 · source CWE mapping

Initialization of a Resource with an Insecure Default

Initialization of a Resource with an Insecure Default represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

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