UBUNTU-CVE-2021-36369 (CVE-2021-36369)

Vulnerability from osv_ubuntu – Published: 2022-10-12 21:15 – Updated: 2025-10-24 04:50 – Source website
VLAI
Details

An issue was discovered in Dropbear through 2020.81. Due to a non-RFC-compliant check of the available authentication methods in the client-side SSH code, it is possible for an SSH server to change the login process in its favor. This attack can bypass additional security measures such as FIDO2 tokens or SSH-Askpass. Thus, it allows an attacker to abuse a forwarded agent for logging on to another server unnoticed.

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

{
  "affected": [
    {
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "dropbear",
            "binary_version": "2016.72-1"
          },
          {
            "binary_name": "dropbear-bin",
            "binary_version": "2016.72-1"
          },
          {
            "binary_name": "dropbear-initramfs",
            "binary_version": "2016.72-1"
          },
          {
            "binary_name": "dropbear-run",
            "binary_version": "2016.72-1"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:16.04:LTS",
        "name": "dropbear",
        "purl": "pkg:deb/ubuntu/dropbear@2016.72-1?arch=source\u0026distro=xenial"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "2014.65-1ubuntu2",
        "2015.68-1",
        "2015.70-1",
        "2015.71-1",
        "2016.72-1"
      ]
    },
    {
      "ecosystem_specific": {
        "availability": "Available with Ubuntu Pro: https://ubuntu.com/pro",
        "binaries": [
          {
            "binary_name": "dropbear",
            "binary_version": "2017.75-3ubuntu0.1~esm1"
          },
          {
            "binary_name": "dropbear-bin",
            "binary_version": "2017.75-3ubuntu0.1~esm1"
          },
          {
            "binary_name": "dropbear-initramfs",
            "binary_version": "2017.75-3ubuntu0.1~esm1"
          },
          {
            "binary_name": "dropbear-run",
            "binary_version": "2017.75-3ubuntu0.1~esm1"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:Pro:18.04:LTS",
        "name": "dropbear",
        "purl": "pkg:deb/ubuntu/dropbear@2017.75-3ubuntu0.1~esm1?arch=source\u0026distro=esm-apps/bionic"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "2017.75-3ubuntu0.1~esm1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "2017.75-2",
        "2017.75-3build1"
      ]
    },
    {
      "ecosystem_specific": {
        "availability": "Available with Ubuntu Pro: https://ubuntu.com/pro",
        "binaries": [
          {
            "binary_name": "dropbear",
            "binary_version": "2019.78-2ubuntu0.1~esm1"
          },
          {
            "binary_name": "dropbear-bin",
            "binary_version": "2019.78-2ubuntu0.1~esm1"
          },
          {
            "binary_name": "dropbear-initramfs",
            "binary_version": "2019.78-2ubuntu0.1~esm1"
          },
          {
            "binary_name": "dropbear-run",
            "binary_version": "2019.78-2ubuntu0.1~esm1"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:Pro:20.04:LTS",
        "name": "dropbear",
        "purl": "pkg:deb/ubuntu/dropbear@2019.78-2ubuntu0.1~esm1?arch=source\u0026distro=esm-apps/focal"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "2019.78-2ubuntu0.1~esm1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "2019.78-2build1"
      ]
    },
    {
      "ecosystem_specific": {
        "availability": "No subscription required",
        "binaries": [
          {
            "binary_name": "dropbear",
            "binary_version": "2020.81-5ubuntu0.1"
          },
          {
            "binary_name": "dropbear-bin",
            "binary_version": "2020.81-5ubuntu0.1"
          },
          {
            "binary_name": "dropbear-initramfs",
            "binary_version": "2020.81-5ubuntu0.1"
          },
          {
            "binary_name": "dropbear-run",
            "binary_version": "2020.81-5ubuntu0.1"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:22.04:LTS",
        "name": "dropbear",
        "purl": "pkg:deb/ubuntu/dropbear@2020.81-5ubuntu0.1?arch=source\u0026distro=jammy"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "2020.81-5ubuntu0.1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "2020.81-3",
        "2020.81-4",
        "2020.81-5"
      ]
    }
  ],
  "aliases": [],
  "details": "An issue was discovered in Dropbear through 2020.81. Due to a non-RFC-compliant check of the available authentication methods in the client-side SSH code, it is possible for an SSH server to change the login process in its favor. This attack can bypass additional security measures such as FIDO2 tokens or SSH-Askpass. Thus, it allows an attacker to abuse a forwarded agent for logging on to another server unnoticed.",
  "id": "UBUNTU-CVE-2021-36369",
  "modified": "2025-10-24T04:50:26Z",
  "published": "2022-10-12T21:15:00Z",
  "references": [
    {
      "type": "REPORT",
      "url": "https://ubuntu.com/security/CVE-2021-36369"
    },
    {
      "type": "REPORT",
      "url": "https://github.com/mkj/dropbear/pull/128"
    },
    {
      "type": "REPORT",
      "url": "https://github.com/mkj/dropbear/releases/tag/DROPBEAR_2022.82"
    },
    {
      "type": "REPORT",
      "url": "https://github.com/mkj/dropbear/releases"
    },
    {
      "type": "REPORT",
      "url": "https://www.cve.org/CVERecord?id=CVE-2021-36369"
    },
    {
      "type": "ADVISORY",
      "url": "https://ubuntu.com/security/notices/USN-7292-1"
    }
  ],
  "related": [
    "USN-7292-1"
  ],
  "schema_version": "1.7.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N",
      "type": "CVSS_V3"
    },
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N",
      "type": "CVSS_V3"
    },
    {
      "score": "medium",
      "type": "Ubuntu"
    }
  ],
  "upstream": [
    "CVE-2021-36369"
  ]
}



Log in or create an account to share your comment.




Tags
Taxonomy of the tags.




Drag nodes to arrange them. Double-click a related vulnerability to open it, or a source to visit its link. The Physics button on the left tunes the layout and the simulation; the legend at the bottom left hides or shows nodes by kind and by sighting type.

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.
Vulnerability timeline

Sightings and recorded dates, grouped by day · UTC

JSON

Loading timeline…




    Related by attack behaviour

    Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.