CVE-2026-12003 (GCVE-0-2026-12003)

Vulnerability from cvelistv5 – Published: 2026-06-16 15:18 – Updated: 2026-08-13 00:28
VLAI
Title
CPython >3.11 Insecure Input Validation resulting in privilege escalation
Summary
To allow builds of Python to be run from an in-tree layout (rather than an installed file layout), the VPATH variable is defined at build time and used to locate certain landmarks - specifically, Modules/setup.local. When this landmark is found relative to VPATH relative to the executable, Python assumes it is running in a source tree and generates a different default sys.path. This code remains in release builds, so that release-ready builds can be built in-tree. On Windows, since builds are written to 'PCbuild/', the value of VPATH is set to '..\..', which results in a landmark of '..\..\Modules\setup.local'. This path is outside the install directory of Python, and may have different permissions, potentially allowing a low-privilege user to create the landmark and an alternative `Lib` folder that will be discovered by an otherwise restricted install. Such a setup occurs with the legacy default install location for all users (in the now superseded EXE installer), due to how Windows allows all users to create folders in the root directory of their OS drive. Our recommended mitigation on Windows is to migrate away from the legacy installer and use the new [Python install manager](https://www.python.org/downloads/latest/pymanager/) to install for the current user. Installs where the directory two levels above the Python installation directory have equivalent permissions are unaffected (in general, a per-user install cannot be modified at all by other users, removing any escalation of privilege risk, and could be directly modified by a privileged user, making the potential tampering irrelevant). Alternative mitigations might include preemptively creating and restricting access to a `Modules` directory. Be aware that only 3.13 and 3.14 will receive updated legacy installers - earlier fixes are only provided as sources. Platforms other than Windows allow VPATH to be overridden, but as they don't usually use a separated directory in the build for binaries, are unlikely to have a landmark reference outside of the install directory. The landmark detection involving VPATH is a fallback for when a more specific landmark - .\pybuilddir.txt - is absent, and was included for compatibility. Future releases of Python will no longer include the fallback, and so builds will need to generate or preserve the pybuilddir.txt file in order to work in-tree. This landmark file has been generated on Windows since 3.11, and on other platforms for longer.
Severity
5.3 (Medium)
CVSS:4.0/AV:L/AC:L/AT:P/PR:L/UI:A/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N
SSVC
Exploitation: none Automatable: no Technical Impact: total
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-06-16 17:53 UTC
CWE
Assigner
PSF CNA under the mitre root
CNA scorecard B 80/100 over 27 records in the last 180 days details
References
Impacted products
Vendor Product Version CPE status
Python Software Foundation CPython Affected: 0 , < 3.11.16 (python)
Affected: 3.12.0 , < 3.12.14 (python)
Affected: 3.13.0 , < 3.13.15 (python)
Affected: 3.14.0 , < 3.14.7 (python)
Affected: 3.15.0a1 , < 3.15.0b3 (python)
guessed Create a notification for this product.
Credits
Jake Yamaki (https://github.com/b6938236) Steve Dower (https://github.com/zooba)
Show details on NVD website
To clipboard 

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                "vulnIntegrityImpact": "HIGH",
                "vulnerabilityResponseEffort": "NOT_DEFINED"
              },
              "source": "cna@python.org",
              "type": "Secondary"
            }
          ],
          "ssvcV203": [
            {
              "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
              "ssvcData": {
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        },
        "published": "2026-06-16T17:16:31.667",
        "references": [
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            "url": "https://github.com/python/cpython/pull/151545"
          },
          {
            "source": "cna@python.org",
            "url": "https://https://mail.python.org/archives/list/security-announce@python.org/thread/JIFOBO7UX3LY4VJKJUOKYJV62CFR2IRH/"
          },
          {
            "source": "af854a3a-2127-422b-91ae-364da2661108",
            "url": "http://www.openwall.com/lists/oss-security/2026/06/16/8"
          }
        ],
        "sourceIdentifier": "cna@python.org",
        "vulnStatus": "Awaiting Analysis",
        "weaknesses": [
          {
            "description": [
              {
                "lang": "en",
                "value": "CWE-427"
              }
            ],
            "source": "cna@python.org",
            "type": "Secondary"
          }
        ]
      }
    },
    "redhat_vex": {
      "aggregate_severity": "Important",
      "current_release_date": "2026-10-02T17:39:40+00:00",
      "cve": "CVE-2026-12003",
      "id": "CVE-2026-12003",
      "initial_release_date": "2026-06-16T15:18:42.998000+00:00",
      "product_status:fixed": "80",
      "product_status:known_affected": "1",
      "product_status:known_not_affected": "131",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "python: Python: Privilege escalation due to insecure VPATH handling in Windows legacy installers",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-12003.json",
      "version": "3"
    },
    "vulnrichment": {
      "containers": {
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          {
            "providerMetadata": {
              "dateUpdated": "2026-06-16T19:12:36.706Z",
              "orgId": "af854a3a-2127-422b-91ae-364da2661108",
              "shortName": "CVE"
            },
            "references": [
              {
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            ],
            "title": "CVE Program Container"
          },
          {
            "metrics": [
              {
                "other": {
                  "content": {
                    "id": "CVE-2026-12003",
                    "options": [
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                      },
                      {
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                      },
                      {
                        "Technical Impact": "total"
                      }
                    ],
                    "role": "CISA Coordinator",
                    "timestamp": "2026-06-16T17:53:54.916961Z",
                    "version": "2.0.3"
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            "providerMetadata": {
              "dateUpdated": "2026-06-16T17:55:24.371Z",
              "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
              "shortName": "CISA-ADP"
            },
            "title": "CISA ADP Vulnrichment"
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        ],
        "cna": {
          "affected": [
            {
              "defaultStatus": "unaffected",
              "product": "CPython",
              "repo": "https://github.com/python/cpython",
              "vendor": "Python Software Foundation",
              "versions": [
                {
                  "lessThan": "3.11.16",
                  "status": "affected",
                  "version": "0",
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                  "status": "affected",
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                  "status": "affected",
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                },
                {
                  "lessThan": "3.15.0b3",
                  "status": "affected",
                  "version": "3.15.0a1",
                  "versionType": "python"
                }
              ]
            }
          ],
          "credits": [
            {
              "lang": "en",
              "type": "reporter",
              "value": "Jake Yamaki (https://github.com/b6938236)"
            },
            {
              "lang": "en",
              "type": "coordinator",
              "value": "Steve Dower (https://github.com/zooba)"
            }
          ],
          "descriptions": [
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              "supportingMedia": [
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                  "type": "text/html",
                  "value": "To allow builds of Python to be run from an in-tree layout (rather than\u003cbr\u003ean installed file layout), the VPATH variable is defined at build time\u003cbr\u003eand used to locate certain landmarks - specifically,\u003cbr\u003eModules/setup.local. When this landmark is found relative to VPATH\u003cbr\u003erelative to the executable, Python assumes it is running in a source\u003cbr\u003etree and generates a different default sys.path. This code remains in\u003cbr\u003erelease builds, so that release-ready builds can be built in-tree.\u003cbr\u003e\u003cbr\u003eOn Windows, since builds are written to \u0027PCbuild/\u0027, the value of\u003cbr\u003eVPATH is set to \u0027..\\..\u0027, which results in a landmark of\u003cbr\u003e\u0027..\\..\\Modules\\setup.local\u0027. This path is outside the install directory\u003cbr\u003eof Python, and may have different permissions, potentially allowing a\u003cbr\u003elow-privilege user to create the landmark and an alternative `Lib`\u003cbr\u003efolder that will be discovered by an otherwise restricted install.\u003cbr\u003e\u003cbr\u003eSuch a setup occurs with the legacy default install location for all\u003cbr\u003eusers (in the now superseded EXE installer), due to how Windows allows\u003cbr\u003eall users to create folders in the root directory of their OS drive.\u003cbr\u003e\u003cbr\u003eOur recommended mitigation on Windows is to migrate away from the\u003cbr\u003elegacy installer and use the new [Python install\u003cbr\u003emanager](https://www.python.org/downloads/latest/pymanager/) to install\u003cbr\u003efor the current user. Installs where the directory two levels above the\u003cbr\u003ePython installation directory have equivalent permissions are unaffected\u003cbr\u003e(in general, a per-user install cannot be modified at all by other\u003cbr\u003eusers, removing any escalation of privilege risk, and could be directly\u003cbr\u003emodified by a privileged user, making the potential tampering\u003cbr\u003eirrelevant). Alternative mitigations might include preemptively creating\u003cbr\u003eand restricting access to a `Modules` directory. Be aware that only 3.13\u003cbr\u003eand 3.14 will receive updated legacy installers - earlier fixes are only\u003cbr\u003eprovided as sources.\u003cbr\u003e\u003cbr\u003ePlatforms other than Windows allow VPATH to be overridden, but as they\u003cbr\u003edon\u0027t usually use a separated directory in the build for binaries, are\u003cbr\u003eunlikely to have a landmark reference outside of the install directory.\u003cbr\u003e\u003cbr\u003eThe landmark detection involving VPATH is a fallback for when a more\u003cbr\u003especific landmark - .\\pybuilddir.txt - is absent, and was included for\u003cbr\u003ecompatibility. Future releases of Python will no longer include the\u003cbr\u003efallback, and so builds will need to generate or preserve the\u003cbr\u003epybuilddir.txt file in order to work in-tree. This landmark file has\u003cbr\u003ebeen generated on Windows since 3.11, and on other platforms for longer."
                }
              ],
              "value": "To allow builds of Python to be run from an in-tree layout (rather than\nan installed file layout), the VPATH variable is defined at build time\nand used to locate certain landmarks - specifically,\nModules/setup.local. When this landmark is found relative to VPATH\nrelative to the executable, Python assumes it is running in a source\ntree and generates a different default sys.path. This code remains in\nrelease builds, so that release-ready builds can be built in-tree.\n\nOn Windows, since builds are written to \u0027PCbuild/\u0027, the value of\nVPATH is set to \u0027..\\..\u0027, which results in a landmark of\n\u0027..\\..\\Modules\\setup.local\u0027. This path is outside the install directory\nof Python, and may have different permissions, potentially allowing a\nlow-privilege user to create the landmark and an alternative `Lib`\nfolder that will be discovered by an otherwise restricted install.\n\nSuch a setup occurs with the legacy default install location for all\nusers (in the now superseded EXE installer), due to how Windows allows\nall users to create folders in the root directory of their OS drive.\n\nOur recommended mitigation on Windows is to migrate away from the\nlegacy installer and use the new [Python install\nmanager](https://www.python.org/downloads/latest/pymanager/) to install\nfor the current user. Installs where the directory two levels above the\nPython installation directory have equivalent permissions are unaffected\n(in general, a per-user install cannot be modified at all by other\nusers, removing any escalation of privilege risk, and could be directly\nmodified by a privileged user, making the potential tampering\nirrelevant). Alternative mitigations might include preemptively creating\nand restricting access to a `Modules` directory. Be aware that only 3.13\nand 3.14 will receive updated legacy installers - earlier fixes are only\nprovided as sources.\n\nPlatforms other than Windows allow VPATH to be overridden, but as they\ndon\u0027t usually use a separated directory in the build for binaries, are\nunlikely to have a landmark reference outside of the install directory.\n\nThe landmark detection involving VPATH is a fallback for when a more\nspecific landmark - .\\pybuilddir.txt - is absent, and was included for\ncompatibility. Future releases of Python will no longer include the\nfallback, and so builds will need to generate or preserve the\npybuilddir.txt file in order to work in-tree. This landmark file has\nbeen generated on Windows since 3.11, and on other platforms for longer."
            }
          ],
          "metrics": [
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                "Automatable": "NOT_DEFINED",
                "Recovery": "NOT_DEFINED",
                "Safety": "NOT_DEFINED",
                "attackComplexity": "LOW",
                "attackRequirements": "PRESENT",
                "attackVector": "LOCAL",
                "baseScore": 5.3,
                "baseSeverity": "MEDIUM",
                "exploitMaturity": "NOT_DEFINED",
                "privilegesRequired": "LOW",
                "providerUrgency": "NOT_DEFINED",
                "subAvailabilityImpact": "NONE",
                "subConfidentialityImpact": "NONE",
                "subIntegrityImpact": "NONE",
                "userInteraction": "ACTIVE",
                "valueDensity": "NOT_DEFINED",
                "vectorString": "CVSS:4.0/AV:L/AC:L/AT:P/PR:L/UI:A/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N",
                "version": "4.0",
                "vulnAvailabilityImpact": "NONE",
                "vulnConfidentialityImpact": "HIGH",
                "vulnIntegrityImpact": "HIGH",
                "vulnerabilityResponseEffort": "NOT_DEFINED"
              },
              "format": "CVSS",
              "scenarios": [
                {
                  "lang": "en",
                  "value": "GENERAL"
                }
              ]
            }
          ],
          "problemTypes": [
            {
              "descriptions": [
                {
                  "cweId": "CWE-427",
                  "description": "CWE-427",
                  "lang": "en",
                  "type": "CWE"
                }
              ]
            }
          ],
          "providerMetadata": {
            "dateUpdated": "2026-08-13T00:28:42.174Z",
            "orgId": "28c92f92-d60d-412d-b760-e73465c3df22",
            "shortName": "PSF"
          },
          "references": [
            {
              "tags": [
                "patch"
              ],
              "url": "https://github.com/python/cpython/pull/151545"
            },
            {
              "tags": [
                "issue-tracking"
              ],
              "url": "https://github.com/python/cpython/issues/151544"
            },
            {
              "tags": [
                "vendor-advisory"
              ],
              "url": "https://https://mail.python.org/archives/list/security-announce@python.org/thread/JIFOBO7UX3LY4VJKJUOKYJV62CFR2IRH/"
            },
            {
              "tags": [
                "patch"
              ],
              "url": "https://github.com/python/cpython/commit/16c40f944b7bff724a403cf4902763d095bb4b2a"
            },
            {
              "tags": [
                "patch"
              ],
              "url": "https://github.com/python/cpython/commit/9e863fab283eddca9c2a8f9d1ee30f4dc243e314"
            },
            {
              "tags": [
                "patch"
              ],
              "url": "https://github.com/python/cpython/commit/a86de0bc236fbb9452f98998fc8437e9fca35700"
            },
            {
              "tags": [
                "patch"
              ],
              "url": "https://github.com/python/cpython/commit/b93d6d3399adbd3a5037b6b92fc3587c85ac5d56"
            },
            {
              "tags": [
                "patch"
              ],
              "url": "https://github.com/python/cpython/commit/03ab7b44788bfd6b8927e16bcdbd025aa08dce06"
            },
            {
              "tags": [
                "patch"
              ],
              "url": "https://github.com/python/cpython/commit/872038377db2e170e0e140b5f8aaedf636b3fbf5"
            }
          ],
          "source": {
            "discovery": "UNKNOWN"
          },
          "title": "CPython \u003e3.11 Insecure Input Validation resulting in privilege escalation",
          "x_generator": {
            "engine": "cvelib 1.8.0"
          }
        }
      },
      "cveMetadata": {
        "assignerOrgId": "28c92f92-d60d-412d-b760-e73465c3df22",
        "assignerShortName": "PSF",
        "cveId": "CVE-2026-12003",
        "datePublished": "2026-06-16T15:18:42.998Z",
        "dateReserved": "2026-06-11T17:05:37.519Z",
        "dateUpdated": "2026-08-13T00:28:42.174Z",
        "state": "PUBLISHED"
      },
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}



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