ubuntu-cve-2021-21261
Vulnerability from osv_ubuntu
Published
2021-01-14 20:15
Modified
2026-04-22 07:39
Summary
Details

Flatpak is a system for building, distributing, and running sandboxed desktop applications on Linux. A bug was discovered in the flatpak-portal service that can allow sandboxed applications to execute arbitrary code on the host system (a sandbox escape). This sandbox-escape bug is present in versions from 0.11.4 and before fixed versions 1.8.5 and 1.10.0. The Flatpak portal D-Bus service (flatpak-portal, also known by its D-Bus service name org.freedesktop.portal.Flatpak) allows apps in a Flatpak sandbox to launch their own subprocesses in a new sandbox instance, either with the same security settings as the caller or with more restrictive security settings. For example, this is used in Flatpak-packaged web browsers such as Chromium to launch subprocesses that will process untrusted web content, and give those subprocesses a more restrictive sandbox than the browser itself. In vulnerable versions, the Flatpak portal service passes caller-specified environment variables to non-sandboxed processes on the host system, and in particular to the flatpak run command that is used to launch the new sandbox instance. A malicious or compromised Flatpak app could set environment variables that are trusted by the flatpak run command, and use them to execute arbitrary code that is not in a sandbox. As a workaround, this vulnerability can be mitigated by preventing the flatpak-portal service from starting, but that mitigation will prevent many Flatpak apps from working correctly. This is fixed in versions 1.8.5 and 1.10.0.

Severity
8.8 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
7.3 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:L/A:N
N/A (UNKNOWN)
medium
References
To clipboard 

{
  "affected": [
    {
      "ecosystem_specific": {
        "availability": "No subscription required",
        "binaries": [
          {
            "binary_name": "flatpak",
            "binary_version": "1.0.9-0ubuntu0.2"
          },
          {
            "binary_name": "flatpak-tests",
            "binary_version": "1.0.9-0ubuntu0.2"
          },
          {
            "binary_name": "gir1.2-flatpak-1.0",
            "binary_version": "1.0.9-0ubuntu0.2"
          },
          {
            "binary_name": "libflatpak0",
            "binary_version": "1.0.9-0ubuntu0.2"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:18.04:LTS",
        "name": "flatpak",
        "purl": "pkg:deb/ubuntu/flatpak@1.0.9-0ubuntu0.2?arch=source\u0026distro=bionic"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "1.0.9-0ubuntu0.2"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "0.8.7-5",
        "0.10.0-1",
        "0.10.0-2",
        "0.10.1-1",
        "0.10.2-1",
        "0.10.2.1-1",
        "0.10.2.1-2",
        "0.10.3-1",
        "0.11.1-0ubuntu1",
        "0.11.3-2",
        "0.11.3-3",
        "0.11.7-0ubuntu0.1",
        "1.0.1-0ubuntu0.1",
        "1.0.6-0ubuntu0.1",
        "1.0.7-0ubuntu0.18.04.1",
        "1.0.8-0ubuntu0.18.04.1",
        "1.0.9-0ubuntu0.1"
      ]
    },
    {
      "ecosystem_specific": {
        "availability": "No subscription required",
        "binaries": [
          {
            "binary_name": "flatpak",
            "binary_version": "1.6.5-0ubuntu0.2"
          },
          {
            "binary_name": "flatpak-tests",
            "binary_version": "1.6.5-0ubuntu0.2"
          },
          {
            "binary_name": "gir1.2-flatpak-1.0",
            "binary_version": "1.6.5-0ubuntu0.2"
          },
          {
            "binary_name": "libflatpak0",
            "binary_version": "1.6.5-0ubuntu0.2"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:20.04:LTS",
        "name": "flatpak",
        "purl": "pkg:deb/ubuntu/flatpak@1.6.5-0ubuntu0.2?arch=source\u0026distro=focal"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "1.6.5-0ubuntu0.2"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "1.4.3-1",
        "1.6.0-1",
        "1.6.1-1",
        "1.6.2-1",
        "1.6.3-1",
        "1.6.5-0ubuntu0.1"
      ]
    }
  ],
  "aliases": [],
  "details": "Flatpak is a system for building, distributing, and running sandboxed desktop applications on Linux. A bug was discovered in the `flatpak-portal` service that can allow sandboxed applications to execute arbitrary code on the host system (a sandbox escape). This sandbox-escape bug is present in versions from 0.11.4 and before fixed versions 1.8.5 and 1.10.0. The Flatpak portal D-Bus service (`flatpak-portal`, also known by its D-Bus service name `org.freedesktop.portal.Flatpak`) allows apps in a Flatpak sandbox to launch their own subprocesses in a new sandbox instance, either with the same security settings as the caller or with more restrictive security settings. For example, this is used in Flatpak-packaged web browsers such as Chromium to launch subprocesses that will process untrusted web content, and give those subprocesses a more restrictive sandbox than the browser itself. In vulnerable versions, the Flatpak portal service passes caller-specified environment variables to non-sandboxed processes on the host system, and in particular to the `flatpak run` command that is used to launch the new sandbox instance. A malicious or compromised Flatpak app could set environment variables that are trusted by the `flatpak run` command, and use them to execute arbitrary code that is not in a sandbox. As a workaround, this vulnerability can be mitigated by preventing the `flatpak-portal` service from starting, but that mitigation will prevent many Flatpak apps from working correctly. This is fixed in versions 1.8.5 and 1.10.0.",
  "id": "UBUNTU-CVE-2021-21261",
  "modified": "2026-04-22T07:39:54Z",
  "published": "2021-01-14T20:15:00Z",
  "references": [
    {
      "type": "REPORT",
      "url": "https://ubuntu.com/security/CVE-2021-21261"
    },
    {
      "type": "REPORT",
      "url": "https://github.com/flatpak/flatpak/security/advisories/GHSA-4ppf-fxf6-vxg2"
    },
    {
      "type": "ADVISORY",
      "url": "https://ubuntu.com/security/notices/USN-4721-1"
    },
    {
      "type": "REPORT",
      "url": "https://www.cve.org/CVERecord?id=CVE-2021-21261"
    }
  ],
  "related": [
    "USN-4721-1"
  ],
  "schema_version": "1.7.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H",
      "type": "CVSS_V3"
    },
    {
      "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:L/A:N",
      "type": "CVSS_V3"
    },
    {
      "score": "medium",
      "type": "Ubuntu"
    }
  ],
  "upstream": [
    "CVE-2021-21261"
  ]
}



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