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CVE Record

CVE-2026-25536: @modelcontextprotocol/sdk has cross-client data leak via shared server/transport instance reuse

MCP TypeScript SDK is the official TypeScript SDK for Model Context Protocol servers and clients. From version 1.10.0 to 1.25.3, cross-client response data leak when a single McpServer/Server and transport instance is reused across multiple client connections, most commonly in stateless StreamableHTTPServerTransport deployments. This issue has been patched in version 1.26.0.

HighCVSS 7.1Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

This flaw can cause an MCP service to send one client's response data to another client when server and transport objects are reused incorrectly. The main business risk is confidential data exposure between authenticated or otherwise permitted clients. The affected SDK range is 1.10.0 through 1.25.3, with a patch in 1.26.0.

Executive priority

Treat as high priority where MCP services process sensitive customer, employee, or operational data. Patch exposed or multi-tenant deployments first.

Technical view

@modelcontextprotocol/typescript-sdk versions >=1.10.0 and <1.26.0 have a cross-client response data leak tied to reuse of a single McpServer/Server and transport instance across connections, commonly stateless StreamableHTTPServerTransport. The CVSS 3.1 score is 7.1, driven by network access, low complexity, low privileges, high confidentiality impact, and low integrity impact.

Likely exposure

Exposure is most likely in MCP deployments using the TypeScript SDK, especially network-accessible stateless HTTP transports that reuse shared server or transport instances across multiple clients.

Exploitation context

The source bundle does not show CISA KEV listing or active exploitation. The condition requires access as a client or low-privileged actor and a vulnerable deployment pattern.

Researcher notes

Evidence supports a concurrency or time-of-check/time-of-use class issue mapped to CWE-362 and CWE-367. The provided sources identify the vulnerable version range, common deployment pattern, and fixed version, but do not provide active exploitation evidence.

Mitigation direction

  • Upgrade @modelcontextprotocol/typescript-sdk to version 1.26.0 or later.
  • Inventory MCP services using TypeScript SDK versions 1.10.0 through 1.25.3.
  • Review stateless StreamableHTTPServerTransport deployments for shared server or transport instance reuse.
  • Apply Red Hat or vendor package advisories where consuming redistributed packages.
  • Monitor upstream advisory GHSA-345p-7cg4-v4c7 for any additional guidance.

Validation and detection

  • Check package manifests, lockfiles, containers, and SBOMs for affected SDK versions.
  • Confirm runtime deployments use @modelcontextprotocol/typescript-sdk 1.26.0 or later.
  • Inspect MCP server initialization for shared McpServer/Server and transport objects across clients.
  • Run regression tests covering concurrent client requests and response isolation.
  • Review logs or reports for unexplained cross-client response mismatches.
Prepared
Confidence
high
Sources
9

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

Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.

cwe · low confidence lookup

CWE-362: Exact CWE lookup

Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.

Open ATT&CK lookup
cwe · low confidence lookup

CWE-367: Exact CWE lookup

Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.

Open ATT&CK lookup
cve · low confidence lookup

CVE-2026-25536 mapping review

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

Open ATT&CK lookup
Vulnerability profileCVE Program record
Severity
High
CVSS
7.1 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:L/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
8Source links

SSVC decision data

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

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
7.1CVSS 3.1HighCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:N2.84.2GitHub_M
7.1CVSS 3.1HighCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:N2.84.2redhat-SADP

Vulnerability scoring details

Base CVSS 3.1 score

7.1High
CVSS 3.1 vector shape for CVE-2026-25536Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

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

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
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-SADP@modelcontextprotocol/sdk: @modelcontextprotocol/sdk cross-client data leak
other:Red Hat severity ratingcvssV3_1
  • 2026-02-04T22:00:54.864Z: Reported to Red Hat.
  • 2026-02-04T21:29:38.276Z: Made public.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
modelcontextprotocoltypescript-sdk>= 1.10.0, < 1.26.0Listed
Weakness

CWE details

CWE-362CWE-367

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

CWE-362 · source CWE mapping

Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')

Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition') represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

Open CWE intelligenceSame-CWE CVEs
CWE-367 · source CWE mapping

Time-of-check Time-of-use (TOCTOU) Race Condition

Time-of-check Time-of-use (TOCTOU) Race Condition represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

Open CWE intelligenceSame-CWE CVEs