GHSA-9M95-8HX6-7P9V

Vulnerability from github – Published: 2022-02-15 01:17 – Updated: 2022-03-15 21:39
VLAI?
Summary
Improper input validation in umoci
Details

Impact

umoci 0.4.6 and earlier can be tricked into modifying host files by creating a malicious layer that has a symlink with the name "." (or "/"). Because umoci deletes inodes if they change types, this results in the rootfs directory being replaced with an attacker-controlled symlink. Subsequent image layers will then be applied on top of the target of the symlink (which could be any directory on the host filesystem the user running umoci has access to).

While umoci does have defences against symlink-based attacks, they are all implemented by resolving things relative to the rootfs directory -- if the rootfs itself is a symlink, umoci resolves it first.

This vulnerability affects both "umoci unpack" and "umoci raw unpack".

Patches

This issue has been patched in umoci 0.4.7, see the references section for the specific commit which fixed this vulnerability.

Workarounds

Note that if you use umoci as an unprivileged user (using the --rootless flag) then umoci will not be able to overwrite any files that your user doesn't have access to. Other possible mitigations are to run umoci under an LSM profile such as AppArmor or SELinux to restrict the level of access it has outside of container image directories.

References

Credits

Thanks to Robin Peraglie from Cure53 for discovering and reporting this vulnerability.

For more information

If you have any questions or comments about this advisory * Open an issue in https://github.com/opencontainers/umoci. * Email us at security@opencontainers.org.

Severity ?
5.5 (Medium)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N
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{
  "affected": [
    {
      "package": {
        "ecosystem": "Go",
        "name": "github.com/opencontainers/umoci"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "0.4.7"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2021-29136"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-20"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2021-05-20T20:13:37Z",
    "nvd_published_at": null,
    "severity": "MODERATE"
  },
  "details": "### Impact\n\numoci 0.4.6 and earlier can be tricked into modifying host files by\ncreating a malicious layer that has a symlink with the name \".\" (or\n\"/\"). Because umoci deletes inodes if they change types, this results in\nthe rootfs directory being replaced with an attacker-controlled symlink.\nSubsequent image layers will then be applied on top of the target of the\nsymlink (which could be any directory on the host filesystem the user\nrunning umoci has access to).\n\nWhile umoci does have defences against symlink-based attacks, they are\nall implemented by resolving things relative to the rootfs directory --\nif the rootfs itself is a symlink, umoci resolves it first.\n\nThis vulnerability affects both \"umoci unpack\" and \"umoci raw unpack\".\n\n### Patches\nThis issue has been patched in umoci 0.4.7, see the references section\nfor the specific commit which fixed this vulnerability.\n\n### Workarounds\nNote that if you use umoci as an unprivileged user (using the --rootless\nflag) then umoci will not be able to overwrite any files that your user\ndoesn\u0027t have access to. Other possible mitigations are to run umoci\nunder an LSM profile such as AppArmor or SELinux to restrict the level\nof access it has outside of container image directories.\n\n### References\n* [oss-security public disclosure](https://www.openwall.com/lists/oss-security/2021/04/06/2)\n* [patch](https://github.com/opencontainers/umoci/commit/d9efc31daf2206f7d3fdb839863cf7a576a2eb57)\n\n### Credits\nThanks to Robin Peraglie from Cure53 for discovering and reporting this\nvulnerability.\n\n### For more information\n\nIf you have any questions or comments about this advisory\n* Open an issue in \u003chttps://github.com/opencontainers/umoci\u003e.\n* Email us at \u003csecurity@opencontainers.org\u003e.",
  "id": "GHSA-9m95-8hx6-7p9v",
  "modified": "2022-03-15T21:39:42Z",
  "published": "2022-02-15T01:17:37Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/opencontainers/umoci/security/advisories/GHSA-9m95-8hx6-7p9v"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2021-29136"
    },
    {
      "type": "WEB",
      "url": "https://github.com/opencontainers/umoci/commit/d9efc31daf2206f7d3fdb839863cf7a576a2eb57"
    },
    {
      "type": "WEB",
      "url": "http://www.openwall.com/lists/oss-security/2021/04/06/2"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Improper input validation in umoci"
}


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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.



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