CVE-2026-121880

{
  "id": "CVE-2026-121880",
  "sourceIdentifier": "8c484e69-127d-402b-9cdb-5f86ef43eb86",
  "published": "2026-11-06T16:17:52.943",
  "lastModified": "2026-11-06T20:38:53.570",
  "vulnStatus": "Awaiting Analysis",
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "Authorization bypass through user-controlled key in the localhost port-proxy (/p/<token>/) in Posit Software, PBC RStudio Server and Posit Workbench before 2026.08.0 allows remote authenticated users to reach web applications and other services bound to 127.0.0.1 under a different user's session, and to view their live rendered content and data, via a proxy URL constructed from the attacker's own port token for an arbitrary port number. The port token is a documented obfuscation measure and not an authorization boundary, and the proxy does not verify that the requested port belongs to the requesting user's session.\n\n\n\nNOTE: exploitation requires an authenticated account on the same multi-user server and a target service listening on localhost at the time of access. Impact may be greater on hosts that co-locate additional privileged localhost services, and the bypass is not prevented by allow-shell=false; no setting restricts the port-proxy without disabling all application proxying."
    }
  ],
  "affected": [
    {
      "source": "8c484e69-127d-402b-9cdb-5f86ef43eb86",
      "affectedData": [
        {
          "vendor": "Posit Software, PBC",
          "product": "Posit Workbench",
          "defaultStatus": "unaffected",
          "collectionURL": "https://posit.co/download/rstudio-server-pro/",
          "cpes": [
            "cpe:2.3:a:posit:workbench:*:*:*:*:*:*:*:*"
          ],
          "modules": [
            "localhost port-proxy (/p/<token>/)"
          ],
          "platforms": [
            "Linux"
          ],
          "programFiles": [
            "src/cpp/core/http/UrlPorts.cpp"
          ],
          "versions": [
            {
              "version": "0",
              "lessThan": "2026.08.0",
              "versionType": "custom",
              "status": "affected"
            }
          ]
        },
        {
          "vendor": "Posit Software, PBC",
          "product": "RStudio Server",
          "defaultStatus": "unaffected",
          "collectionURL": "https://posit.co/download/rstudio-server/",
          "cpes": [
            "cpe:2.3:a:posit:rstudio_server:*:*:*:*:*:*:*:*"
          ],
          "modules": [
            "localhost port-proxy (/p/<token>/)"
          ],
          "platforms": [
            "Linux"
          ],
          "programFiles": [
            "src/cpp/core/http/UrlPorts.cpp"
          ],
          "versions": [
            {
              "version": "0",
              "lessThan": "2026.08.0",
              "versionType": "custom",
              "status": "affected"
            }
          ]
        }
      ]
    }
  ],
  "metrics": {
    "cvssMetricV40": [
      {
        "source": "8c484e69-127d-402b-9cdb-5f86ef43eb86",
        "type": "Secondary",
        "cvssData": {
          "version": "4.0",
          "vectorString": "CVSS:4.0/AV:L/AC:L/AT:P/PR:L/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:P/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:Y/R:A/V:D/RE:M/U:Amber",
          "baseScore": 4.7,
          "baseSeverity": "MEDIUM",
          "attackVector": "LOCAL",
          "attackComplexity": "LOW",
          "attackRequirements": "PRESENT",
          "privilegesRequired": "LOW",
          "userInteraction": "NONE",
          "vulnConfidentialityImpact": "HIGH",
          "vulnIntegrityImpact": "NONE",
          "vulnAvailabilityImpact": "NONE",
          "subConfidentialityImpact": "NONE",
          "subIntegrityImpact": "NONE",
          "subAvailabilityImpact": "NONE",
          "exploitMaturity": "PROOF_OF_CONCEPT",
          "confidentialityRequirement": "NOT_DEFINED",
          "integrityRequirement": "NOT_DEFINED",
          "availabilityRequirement": "NOT_DEFINED",
          "modifiedAttackVector": "NOT_DEFINED",
          "modifiedAttackComplexity": "NOT_DEFINED",
          "modifiedAttackRequirements": "NOT_DEFINED",
          "modifiedPrivilegesRequired": "NOT_DEFINED",
          "modifiedUserInteraction": "NOT_DEFINED",
          "modifiedVulnConfidentialityImpact": "NOT_DEFINED",
          "modifiedVulnIntegrityImpact": "NOT_DEFINED",
          "modifiedVulnAvailabilityImpact": "NOT_DEFINED",
          "modifiedSubConfidentialityImpact": "NOT_DEFINED",
          "modifiedSubIntegrityImpact": "NOT_DEFINED",
          "modifiedSubAvailabilityImpact": "NOT_DEFINED",
          "Safety": "NOT_DEFINED",
          "Automatable": "YES",
          "Recovery": "AUTOMATIC",
          "valueDensity": "DIFFUSE",
          "vulnerabilityResponseEffort": "MODERATE",
          "providerUrgency": "AMBER"
        }
      }
    ],
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "timestamp": "2026-11-06T17:21:05.517519Z",
          "id": "CVE-2026-121880",
          "options": [
            {
              "exploitation": "none"
            },
            {
              "automatable": "no"
            },
            {
              "technicalImpact": "partial"
            }
          ],
          "role": "CISA Coordinator",
          "version": "2.0.3"
        }
      }
    ]
  },
  "weaknesses": [
    {
      "source": "8c484e69-127d-402b-9cdb-5f86ef43eb86",
      "type": "Secondary",
      "description": [
        {
          "lang": "en",
          "value": "CWE-639"
        },
        {
          "lang": "en",
          "value": "CWE-862"
        }
      ]
    }
  ],
  "references": [
    {
      "url": "https://docs.posit.co/ide/news/#rstudio-2026.08.0",
      "source": "8c484e69-127d-402b-9cdb-5f86ef43eb86"
    },
    {
      "url": "https://trust.posit.co/updates",
      "source": "8c484e69-127d-402b-9cdb-5f86ef43eb86"
    }
  ]
}