CVE-2026-108859 (GCVE-0-2026-108859)

Vulnerability from cvelistv5 – Published: 2026-10-11 13:26 – Updated: 2026-10-11 13:26
VLAI
Title
mcp-go through 1.2.1 Denial of Service via Unbounded POST Body Buffering
Summary
mcp-go through 1.2.1 contains a denial of service vulnerability in StreamableHTTPServer.ServeHTTP that allows remote unauthenticated attackers to exhaust memory by sending oversized POST bodies. Attackers can send arbitrarily large or many concurrent POST requests, read fully via io.ReadAll before validation, to degrade or OOM-kill the server process.
Severity
8.7 (High)
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
7.5 (High)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CWE
  • CWE-770 - Allocation of Resources Without Limits or Throttling
Assigner
VulnCheck CNA under the mitre root
CNA scorecard B 84/100 over 5802 records in the last 180 days details
References
Impacted products
Vendor Product Version CPE status
mark3labs mcp-go Affected: 0 , ≤ 1.2.1 (semver)
guessed Create a notification for this product.
Date Public
2026-10-11 00:00
Credits
hieuPenguinnn
Show details on NVD website
To clipboard 

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              "version": "0",
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        }
      ],
      "metrics": [
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            "subConfidentialityImpact": "NONE",
            "subIntegrityImpact": "NONE",
            "userInteraction": "NONE",
            "vectorString": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N",
            "version": "4.0",
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            "baseSeverity": "HIGH",
            "confidentialityImpact": "NONE",
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            "scope": "UNCHANGED",
            "userInteraction": "NONE",
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              "description": "Allocation of Resources Without Limits or Throttling",
              "lang": "en",
              "type": "CWE"
            }
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      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-11T13:26:06.450Z",
        "orgId": "83251b91-4cc7-4094-a5c7-464a1b83ea10",
        "shortName": "VulnCheck"
      },
      "references": [
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          "tags": [
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          "url": "https://hackmd.io/@1ExmmukzRMWN7B4gQ4W-4Q/mark3labs-mcp-go-streamable-http-unbounded-body"
        },
        {
          "tags": [
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          "url": "https://github.com/mark3labs/mcp-go/blob/90d247ed8d45cbb7d71d9a95e112789b78760443/server/streamable_http.go#L405-L411"
        },
        {
          "tags": [
            "product"
          ],
          "url": "https://github.com/mark3labs/mcp-go"
        },
        {
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          "tags": [
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          "url": "https://www.vulncheck.com/advisories/mcp-go-through-1.2.1-denial-of-service-via-unbounded-post-body-buffering"
        }
      ],
      "title": "mcp-go through 1.2.1 Denial of Service via Unbounded POST Body Buffering",
      "x_generator": {
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  "cveMetadata": {
    "assignerOrgId": "83251b91-4cc7-4094-a5c7-464a1b83ea10",
    "assignerShortName": "VulnCheck",
    "cveId": "CVE-2026-108859",
    "datePublished": "2026-10-11T13:26:06.450Z",
    "dateReserved": "2026-10-11T13:06:49.278Z",
    "dateUpdated": "2026-10-11T13:26:06.450Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "epss": {
      "cve": "CVE-2026-108859",
      "date": "2026-10-12",
      "epss": "0.00545",
      "percentile": "0.4414"
    },
    "nvd": {
      "cve": {
        "affected": [
          {
            "affectedData": [
              {
                "defaultStatus": "unaffected",
                "packageURL": "pkg:golang/github.com/mark3labs/mcp-go",
                "product": "mcp-go",
                "repo": "https://github.com/mark3labs/mcp-go",
                "vendor": "mark3labs",
                "versions": [
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                    "status": "affected",
                    "version": "0",
                    "versionType": "semver"
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        "cveTags": [],
        "descriptions": [
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            "value": "mcp-go through 1.2.1 contains a denial of service vulnerability in StreamableHTTPServer.ServeHTTP that allows remote unauthenticated attackers to exhaust memory by sending oversized POST bodies. Attackers can send arbitrarily large or many concurrent POST requests, read fully via io.ReadAll before validation, to degrade or OOM-kill the server process."
          }
        ],
        "id": "CVE-2026-108859",
        "lastModified": "2026-10-11T14:17:05.893",
        "metrics": {
          "cvssMetricV31": [
            {
              "cvssData": {
                "attackComplexity": "LOW",
                "attackVector": "NETWORK",
                "availabilityImpact": "HIGH",
                "baseScore": 7.5,
                "baseSeverity": "HIGH",
                "confidentialityImpact": "NONE",
                "integrityImpact": "NONE",
                "privilegesRequired": "NONE",
                "scope": "UNCHANGED",
                "userInteraction": "NONE",
                "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
                "version": "3.1"
              },
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              "impactScore": 3.6,
              "source": "disclosure@vulncheck.com",
              "type": "Primary"
            }
          ],
          "cvssMetricV40": [
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              "cvssData": {
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                "Recovery": "NOT_DEFINED",
                "Safety": "NOT_DEFINED",
                "attackComplexity": "LOW",
                "attackRequirements": "NONE",
                "attackVector": "NETWORK",
                "availabilityRequirement": "NOT_DEFINED",
                "baseScore": 8.7,
                "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": "NONE",
                "subIntegrityImpact": "NONE",
                "userInteraction": "NONE",
                "valueDensity": "NOT_DEFINED",
                "vectorString": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/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",
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                "vulnIntegrityImpact": "NONE",
                "vulnerabilityResponseEffort": "NOT_DEFINED"
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              "source": "disclosure@vulncheck.com",
              "type": "Secondary"
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        "references": [
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            "source": "disclosure@vulncheck.com",
            "url": "https://github.com/mark3labs/mcp-go"
          },
          {
            "source": "disclosure@vulncheck.com",
            "url": "https://github.com/mark3labs/mcp-go/blob/90d247ed8d45cbb7d71d9a95e112789b78760443/server/streamable_http.go#L405-L411"
          },
          {
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          },
          {
            "source": "disclosure@vulncheck.com",
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        "sourceIdentifier": "disclosure@vulncheck.com",
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    "redhat_vex": {
      "aggregate_severity": "Important",
      "current_release_date": "2026-10-12T04:12:05+00:00",
      "cve": "CVE-2026-108859",
      "id": "CVE-2026-108859",
      "initial_release_date": "2026-10-11T13:26:06.450000+00:00",
      "product_status:known_affected": "7",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "github.com/mark3labs/mcp-go: mcp-go: Denial of Service via unbounded HTTP request body buffering",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-108859.json",
      "version": "3"
    }
  }
}



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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

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Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
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  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.



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