MSRC_CVE-2019-18276

Vulnerability from csaf_microsoft - Published: 2019-11-02 00:00 - Updated: 2020-08-18 00:00
Summary
An issue was discovered in disable_priv_mode in shell.c in GNU Bash through 5.0 patch 11. By default if Bash is run with its effective UID not equal to its real UID it will drop privileges by setting its effective UID to its real UID. However it does so incorrectly. On Linux and other systems that support "saved UID" functionality the saved UID is not dropped. An attacker with command execution in the shell can use "enable -f" for runtime loading of a new builtin which can be a shared object that calls setuid() and therefore regains privileges. However binaries running with an effective UID of 0 are unaffected.

Notes

Additional Resources
To determine the support lifecycle for your software, see the Microsoft Support Lifecycle: https://support.microsoft.com/lifecycle
Disclaimer
The information provided in the Microsoft Knowledge Base is provided \"as is\" without warranty of any kind. Microsoft disclaims all warranties, either express or implied, including the warranties of merchantability and fitness for a particular purpose. In no event shall Microsoft Corporation or its suppliers be liable for any damages whatsoever including direct, indirect, incidental, consequential, loss of business profits or special damages, even if Microsoft Corporation or its suppliers have been advised of the possibility of such damages. Some states do not allow the exclusion or limitation of liability for consequential or incidental damages so the foregoing limitation may not apply.
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{
  "document": {
    "category": "csaf_vex",
    "csaf_version": "2.0",
    "distribution": {
      "text": "Public",
      "tlp": {
        "label": "WHITE",
        "url": "https://www.first.org/tlp/"
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    "lang": "en-US",
    "notes": [
      {
        "category": "general",
        "text": "To determine the support lifecycle for your software, see the Microsoft Support Lifecycle: https://support.microsoft.com/lifecycle",
        "title": "Additional Resources"
      },
      {
        "category": "legal_disclaimer",
        "text": "The information provided in the Microsoft Knowledge Base is provided \\\"as is\\\" without warranty of any kind. Microsoft disclaims all warranties, either express or implied, including the warranties of merchantability and fitness for a particular purpose. In no event shall Microsoft Corporation or its suppliers be liable for any damages whatsoever including direct, indirect, incidental, consequential, loss of business profits or special damages, even if Microsoft Corporation or its suppliers have been advised of the possibility of such damages. Some states do not allow the exclusion or limitation of liability for consequential or incidental damages so the foregoing limitation may not apply.",
        "title": "Disclaimer"
      }
    ],
    "publisher": {
      "category": "vendor",
      "contact_details": "secure@microsoft.com",
      "name": "Microsoft Security Response Center",
      "namespace": "https://msrc.microsoft.com"
    },
    "references": [
      {
        "category": "self",
        "summary": "CVE-2019-18276 An issue was discovered in disable_priv_mode in shell.c in GNU Bash through 5.0 patch 11. By default if Bash is run with its effective UID not equal to its real UID it will drop privileges by setting its effective UID to its real UID. However it does so incorrectly. On Linux and other systems that support \"saved UID\" functionality the saved UID is not dropped. An attacker with command execution in the shell can use \"enable -f\" for runtime loading of a new builtin which can be a shared object that calls setuid() and therefore regains privileges. However binaries running with an effective UID of 0 are unaffected. - VEX",
        "url": "https://msrc.microsoft.com/csaf/vex/2019/msrc_cve-2019-18276.json"
      },
      {
        "category": "external",
        "summary": "Microsoft Support Lifecycle",
        "url": "https://support.microsoft.com/lifecycle"
      },
      {
        "category": "external",
        "summary": "Common Vulnerability Scoring System",
        "url": "https://www.first.org/cvss"
      }
    ],
    "title": "An issue was discovered in disable_priv_mode in shell.c in GNU Bash through 5.0 patch 11. By default if Bash is run with its effective UID not equal to its real UID it will drop privileges by setting its effective UID to its real UID. However it does so incorrectly. On Linux and other systems that support \"saved UID\" functionality the saved UID is not dropped. An attacker with command execution in the shell can use \"enable -f\" for runtime loading of a new builtin which can be a shared object that calls setuid() and therefore regains privileges. However binaries running with an effective UID of 0 are unaffected.",
    "tracking": {
      "current_release_date": "2020-08-18T00:00:00.000Z",
      "generator": {
        "date": "2025-10-19T17:46:18.334Z",
        "engine": {
          "name": "MSRC Generator",
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      },
      "id": "msrc_CVE-2019-18276",
      "initial_release_date": "2019-11-02T00:00:00.000Z",
      "revision_history": [
        {
          "date": "2020-08-18T00:00:00.000Z",
          "legacy_version": "1",
          "number": "1",
          "summary": "Information published."
        }
      ],
      "status": "final",
      "version": "1"
    }
  },
  "product_tree": {
    "branches": [
      {
        "branches": [
          {
            "branches": [
              {
                "category": "product_version",
                "name": "1.0",
                "product": {
                  "name": "CBL Mariner 1.0",
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                }
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            "name": "Azure Linux"
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          {
            "branches": [
              {
                "category": "product_version_range",
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              {
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            ],
            "category": "product_name",
            "name": "bash"
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        "name": "Microsoft"
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    "relationships": [
      {
        "category": "default_component_of",
        "full_product_name": {
          "name": "\u003ccm1 bash 4.4.18-6 as a component of CBL Mariner 1.0",
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        "relates_to_product_reference": "16820"
      },
      {
        "category": "default_component_of",
        "full_product_name": {
          "name": "cm1 bash 4.4.18-6 as a component of CBL Mariner 1.0",
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        "product_reference": "17031",
        "relates_to_product_reference": "16820"
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    ]
  },
  "vulnerabilities": [
    {
      "cve": "CVE-2019-18276",
      "cwe": {
        "id": "CWE-273",
        "name": "Improper Check for Dropped Privileges"
      },
      "notes": [
        {
          "category": "general",
          "text": "mitre",
          "title": "Assigning CNA"
        }
      ],
      "product_status": {
        "fixed": [
          "17031-16820"
        ],
        "known_affected": [
          "16820-1"
        ]
      },
      "references": [
        {
          "category": "self",
          "summary": "CVE-2019-18276 An issue was discovered in disable_priv_mode in shell.c in GNU Bash through 5.0 patch 11. By default if Bash is run with its effective UID not equal to its real UID it will drop privileges by setting its effective UID to its real UID. However it does so incorrectly. On Linux and other systems that support \"saved UID\" functionality the saved UID is not dropped. An attacker with command execution in the shell can use \"enable -f\" for runtime loading of a new builtin which can be a shared object that calls setuid() and therefore regains privileges. However binaries running with an effective UID of 0 are unaffected. - VEX",
          "url": "https://msrc.microsoft.com/csaf/vex/2019/msrc_cve-2019-18276.json"
        }
      ],
      "remediations": [
        {
          "category": "vendor_fix",
          "date": "2020-08-18T00:00:00.000Z",
          "details": "4.4.18-6:Security Update:https://learn.microsoft.com/en-us/azure/azure-linux/tutorial-azure-linux-upgrade",
          "product_ids": [
            "16820-1"
          ],
          "url": "https://learn.microsoft.com/en-us/azure/azure-linux/tutorial-azure-linux-upgrade"
        }
      ],
      "scores": [
        {
          "cvss_v3": {
            "attackComplexity": "LOW",
            "attackVector": "LOCAL",
            "availabilityImpact": "HIGH",
            "baseScore": 7.8,
            "baseSeverity": "HIGH",
            "confidentialityImpact": "HIGH",
            "environmentalsScore": 0.0,
            "integrityImpact": "HIGH",
            "privilegesRequired": "LOW",
            "scope": "UNCHANGED",
            "temporalScore": 7.8,
            "userInteraction": "NONE",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "products": [
            "16820-1"
          ]
        }
      ],
      "title": "An issue was discovered in disable_priv_mode in shell.c in GNU Bash through 5.0 patch 11. By default if Bash is run with its effective UID not equal to its real UID it will drop privileges by setting its effective UID to its real UID. However it does so incorrectly. On Linux and other systems that support \"saved UID\" functionality the saved UID is not dropped. An attacker with command execution in the shell can use \"enable -f\" for runtime loading of a new builtin which can be a shared object that calls setuid() and therefore regains privileges. However binaries running with an effective UID of 0 are unaffected."
    }
  ]
}


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  • 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.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • 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.



Detection rules are retrieved from Rulezet.