ubuntu-cve-2021-21381
Vulnerability from osv_ubuntu
Published
2021-03-11 17:15
Modified
2026-04-22 07:39
Summary
Details

Flatpak is a system for building, distributing, and running sandboxed desktop applications on Linux. In Flatpack since version 0.9.4 and before version 1.10.2 has a vulnerability in the "file forwarding" feature which can be used by an attacker to gain access to files that would not ordinarily be allowed by the app's permissions. By putting the special tokens @@ and/or @@u in the Exec field of a Flatpak app's .desktop file, a malicious app publisher can trick flatpak into behaving as though the user had chosen to open a target file with their Flatpak app, which automatically makes that file available to the Flatpak app. This is fixed in version 1.10.2. A minimal solution is the first commit "Disallow @@ and @@U usage in desktop files". The follow-up commits "dir: Reserve the whole @@ prefix" and "dir: Refuse to export .desktop files with suspicious uses of @@ tokens" are recommended, but not strictly required. As a workaround, avoid installing Flatpak apps from untrusted sources, or check the contents of the exported .desktop files in exports/share/applications/*.desktop (typically ~/.local/share/flatpak/exports/share/applications/*.desktop and /var/lib/flatpak/exports/share/applications/*.desktop) to make sure that literal filenames do not follow @@ or @@u.

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

{
  "affected": [
    {
      "ecosystem_specific": {
        "availability": "No subscription required",
        "binaries": [
          {
            "binary_name": "flatpak",
            "binary_version": "1.0.9-0ubuntu0.3"
          },
          {
            "binary_name": "flatpak-tests",
            "binary_version": "1.0.9-0ubuntu0.3"
          },
          {
            "binary_name": "gir1.2-flatpak-1.0",
            "binary_version": "1.0.9-0ubuntu0.3"
          },
          {
            "binary_name": "libflatpak0",
            "binary_version": "1.0.9-0ubuntu0.3"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:18.04:LTS",
        "name": "flatpak",
        "purl": "pkg:deb/ubuntu/flatpak@1.0.9-0ubuntu0.3?arch=source\u0026distro=bionic"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "1.0.9-0ubuntu0.3"
            }
          ],
          "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",
        "1.0.9-0ubuntu0.2"
      ]
    },
    {
      "ecosystem_specific": {
        "availability": "No subscription required",
        "binaries": [
          {
            "binary_name": "flatpak",
            "binary_version": "1.6.5-0ubuntu0.3"
          },
          {
            "binary_name": "flatpak-tests",
            "binary_version": "1.6.5-0ubuntu0.3"
          },
          {
            "binary_name": "gir1.2-flatpak-1.0",
            "binary_version": "1.6.5-0ubuntu0.3"
          },
          {
            "binary_name": "libflatpak0",
            "binary_version": "1.6.5-0ubuntu0.3"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:20.04:LTS",
        "name": "flatpak",
        "purl": "pkg:deb/ubuntu/flatpak@1.6.5-0ubuntu0.3?arch=source\u0026distro=focal"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "1.6.5-0ubuntu0.3"
            }
          ],
          "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",
        "1.6.5-0ubuntu0.2"
      ]
    }
  ],
  "aliases": [],
  "details": "Flatpak is a system for building, distributing, and running sandboxed desktop applications on Linux. In Flatpack since version 0.9.4 and before version 1.10.2 has a vulnerability in the \"file forwarding\" feature which can be used by an attacker to gain access to files that would not ordinarily be allowed by the app\u0027s permissions. By putting the special tokens `@@` and/or `@@u` in the Exec field of a Flatpak app\u0027s .desktop file, a malicious app publisher can trick flatpak into behaving as though the user had chosen to open a target file with their Flatpak app, which automatically makes that file available to the Flatpak app. This is fixed in version 1.10.2. A minimal solution is the first commit \"`Disallow @@ and @@U usage in desktop files`\". The follow-up commits \"`dir: Reserve the whole @@ prefix`\" and \"`dir: Refuse to export .desktop files with suspicious uses of @@ tokens`\" are recommended, but not strictly required. As a workaround, avoid installing Flatpak apps from untrusted sources, or check the contents of the exported `.desktop` files in `exports/share/applications/*.desktop` (typically `~/.local/share/flatpak/exports/share/applications/*.desktop` and `/var/lib/flatpak/exports/share/applications/*.desktop`) to make sure that literal filenames do not follow `@@` or `@@u`.",
  "id": "UBUNTU-CVE-2021-21381",
  "modified": "2026-04-22T07:39:54Z",
  "published": "2021-03-11T17:15:00Z",
  "references": [
    {
      "type": "REPORT",
      "url": "https://ubuntu.com/security/CVE-2021-21381"
    },
    {
      "type": "REPORT",
      "url": "https://github.com/flatpak/flatpak/issues/4146"
    },
    {
      "type": "REPORT",
      "url": "https://github.com/flatpak/flatpak/security/advisories/GHSA-xgh4-387p-hqpp"
    },
    {
      "type": "REPORT",
      "url": "https://github.com/flatpak/flatpak/commit/8279c5818425b6812523e3805bbe242fb6a5d961"
    },
    {
      "type": "REPORT",
      "url": "https://github.com/flatpak/flatpak/commit/a7401e638bf0c03102039e216ab1081922f140ae"
    },
    {
      "type": "REPORT",
      "url": "https://github.com/flatpak/flatpak/commit/eb7946bb6248923d8c90fe9b84425fef97ae580d"
    },
    {
      "type": "REPORT",
      "url": "https://github.com/flatpak/flatpak/pull/4156"
    },
    {
      "type": "REPORT",
      "url": "https://github.com/flatpak/flatpak/releases/tag/1.10.2"
    },
    {
      "type": "ADVISORY",
      "url": "https://ubuntu.com/security/notices/USN-4951-1"
    },
    {
      "type": "REPORT",
      "url": "https://www.cve.org/CVERecord?id=CVE-2021-21381"
    }
  ],
  "related": [
    "USN-4951-1"
  ],
  "schema_version": "1.7.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N",
      "type": "CVSS_V3"
    },
    {
      "score": "CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:C/C:L/I:H/A:N",
      "type": "CVSS_V3"
    },
    {
      "score": "medium",
      "type": "Ubuntu"
    }
  ],
  "upstream": [
    "CVE-2021-21381"
  ]
}



Log in or create an account to share your comment.




Tags
Taxonomy of the tags.





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

Author Source Type Date Other

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.
  • 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.