ubuntu-cve-2021-21404
Vulnerability from osv_ubuntu
Published
2021-04-06 20:15
Modified
2026-07-02 15:50
Summary
Details

Syncthing is a continuous file synchronization program. In Syncthing before version 1.15.0, the relay server strelaysrv can be caused to crash and exit by sending a relay message with a negative length field. Similarly, Syncthing itself can crash for the same reason if given a malformed message from a malicious relay server when attempting to join the relay. Relay joins are essentially random (from a subset of low latency relays) and Syncthing will by default restart when crashing, at which point it's likely to pick another non-malicious relay. This flaw is fixed in version 1.15.0.

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

{
  "affected": [
    {
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "golang-github-syncthing-syncthing-dev",
            "binary_version": "0.14.43+ds1-6"
          },
          {
            "binary_name": "syncthing",
            "binary_version": "0.14.43+ds1-6"
          },
          {
            "binary_name": "syncthing-discosrv",
            "binary_version": "0.14.43+ds1-6"
          },
          {
            "binary_name": "syncthing-relaysrv",
            "binary_version": "0.14.43+ds1-6"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:18.04:LTS",
        "name": "syncthing",
        "purl": "pkg:deb/ubuntu/syncthing@0.14.43+ds1-6?arch=source\u0026distro=bionic"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "0.14.36+ds1-1",
        "0.14.38+ds1-1",
        "0.14.43+ds1-5",
        "0.14.43+ds1-6"
      ]
    },
    {
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "golang-github-syncthing-syncthing-dev",
            "binary_version": "1.1.4~ds1-4ubuntu1.2"
          },
          {
            "binary_name": "syncthing",
            "binary_version": "1.1.4~ds1-4ubuntu1.2"
          },
          {
            "binary_name": "syncthing-discosrv",
            "binary_version": "1.1.4~ds1-4ubuntu1.2"
          },
          {
            "binary_name": "syncthing-relaysrv",
            "binary_version": "1.1.4~ds1-4ubuntu1.2"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:20.04:LTS",
        "name": "syncthing",
        "purl": "pkg:deb/ubuntu/syncthing@1.1.4~ds1-4ubuntu1.2?arch=source\u0026distro=focal"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "1.1.4~ds1-4",
        "1.1.4~ds1-4ubuntu1",
        "1.1.4~ds1-4ubuntu1.1",
        "1.1.4~ds1-4ubuntu1.2"
      ]
    },
    {
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "golang-github-syncthing-syncthing-dev",
            "binary_version": "1.18.0~ds1-3ubuntu0.3+esm2"
          },
          {
            "binary_name": "syncthing",
            "binary_version": "1.18.0~ds1-3ubuntu0.3+esm2"
          },
          {
            "binary_name": "syncthing-discosrv",
            "binary_version": "1.18.0~ds1-3ubuntu0.3+esm2"
          },
          {
            "binary_name": "syncthing-relaysrv",
            "binary_version": "1.18.0~ds1-3ubuntu0.3+esm2"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:Pro:22.04:LTS",
        "name": "syncthing",
        "purl": "pkg:deb/ubuntu/syncthing@1.18.0~ds1-3ubuntu0.3+esm2?arch=source\u0026distro=esm-apps/jammy"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "1.12.1~ds1-4",
        "1.18.0~ds1-3",
        "1.18.0~ds1-3ubuntu0.1",
        "1.18.0~ds1-3ubuntu0.2",
        "1.18.0~ds1-3ubuntu0.3",
        "1.18.0~ds1-3ubuntu0.3+esm1",
        "1.18.0~ds1-3ubuntu0.3+esm2"
      ]
    },
    {
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "golang-github-syncthing-syncthing-dev",
            "binary_version": "1.27.2~ds4-1ubuntu0.24.04.3+esm2"
          },
          {
            "binary_name": "syncthing",
            "binary_version": "1.27.2~ds4-1ubuntu0.24.04.3+esm2"
          },
          {
            "binary_name": "syncthing-discosrv",
            "binary_version": "1.27.2~ds4-1ubuntu0.24.04.3+esm2"
          },
          {
            "binary_name": "syncthing-relaysrv",
            "binary_version": "1.27.2~ds4-1ubuntu0.24.04.3+esm2"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:Pro:24.04:LTS",
        "name": "syncthing",
        "purl": "pkg:deb/ubuntu/syncthing@1.27.2~ds4-1ubuntu0.24.04.3+esm2?arch=source\u0026distro=esm-apps/noble"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "1.19.2~ds1-3",
        "1.27.2~ds4-1",
        "1.27.2~ds4-1ubuntu0.24.04.1",
        "1.27.2~ds4-1ubuntu0.24.04.2",
        "1.27.2~ds4-1ubuntu0.24.04.2+esm1",
        "1.27.2~ds4-1ubuntu0.24.04.3",
        "1.27.2~ds4-1ubuntu0.24.04.3+esm1",
        "1.27.2~ds4-1ubuntu0.24.04.3+esm2"
      ]
    },
    {
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "golang-github-syncthing-syncthing-dev",
            "binary_version": "1.29.5~ds1-2"
          },
          {
            "binary_name": "syncthing",
            "binary_version": "1.29.5~ds1-2"
          },
          {
            "binary_name": "syncthing-discosrv",
            "binary_version": "1.29.5~ds1-2"
          },
          {
            "binary_name": "syncthing-relaysrv",
            "binary_version": "1.29.5~ds1-2"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:25.10",
        "name": "syncthing",
        "purl": "pkg:deb/ubuntu/syncthing@1.29.5~ds1-2?arch=source\u0026distro=questing"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "1.29.2~ds1-1",
        "1.29.5~ds1-2"
      ]
    },
    {
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "golang-github-syncthing-syncthing-dev",
            "binary_version": "1.29.5~ds1-3ubuntu0.26.04.1~esm1"
          },
          {
            "binary_name": "syncthing",
            "binary_version": "1.29.5~ds1-3ubuntu0.26.04.1~esm1"
          },
          {
            "binary_name": "syncthing-discosrv",
            "binary_version": "1.29.5~ds1-3ubuntu0.26.04.1~esm1"
          },
          {
            "binary_name": "syncthing-relaysrv",
            "binary_version": "1.29.5~ds1-3ubuntu0.26.04.1~esm1"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:Pro:26.04:LTS",
        "name": "syncthing",
        "purl": "pkg:deb/ubuntu/syncthing@1.29.5~ds1-3ubuntu0.26.04.1~esm1?arch=source\u0026distro=esm-apps/resolute"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "1.29.5~ds1-2",
        "1.29.5~ds1-3",
        "1.29.5~ds1-3ubuntu0.26.04.1~esm1"
      ]
    }
  ],
  "aliases": [],
  "details": "Syncthing is a continuous file synchronization program. In Syncthing before version 1.15.0, the relay server `strelaysrv` can be caused to crash and exit by sending a relay message with a negative length field. Similarly, Syncthing itself can crash for the same reason if given a malformed message from a malicious relay server when attempting to join the relay. Relay joins are essentially random (from a subset of low latency relays) and Syncthing will by default restart when crashing, at which point it\u0027s likely to pick another non-malicious relay. This flaw is fixed in version 1.15.0.",
  "id": "UBUNTU-CVE-2021-21404",
  "modified": "2026-07-02T15:50:24Z",
  "published": "2021-04-06T20:15:00Z",
  "references": [
    {
      "type": "REPORT",
      "url": "https://ubuntu.com/security/CVE-2021-21404"
    },
    {
      "type": "REPORT",
      "url": "https://github.com/syncthing/syncthing/commit/fb4fdaf4c0a79c22cad000c42ac1394e3ccb6a97"
    },
    {
      "type": "REPORT",
      "url": "https://github.com/syncthing/syncthing/releases/tag/v1.15.0"
    },
    {
      "type": "REPORT",
      "url": "https://github.com/syncthing/syncthing/security/advisories/GHSA-x462-89pf-6r5h"
    },
    {
      "type": "REPORT",
      "url": "https://pkg.go.dev/github.com/syncthing/syncthing"
    },
    {
      "type": "REPORT",
      "url": "https://www.cve.org/CVERecord?id=CVE-2021-21404"
    }
  ],
  "related": [],
  "schema_version": "1.7.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    },
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    },
    {
      "score": "medium",
      "type": "Ubuntu"
    }
  ],
  "upstream": [
    "CVE-2021-21404"
  ]
}



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