UBUNTU-CVE-2021-21404

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Source
https://ubuntu.com/security/CVE-2021-21404
Import Source
https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2021/UBUNTU-CVE-2021-21404.json
JSON Data
https://api.osv.dev/v1/vulns/UBUNTU-CVE-2021-21404
Upstream
Published
2021-04-06T20:15:00Z
Modified
2025-10-24T04:50:06Z
Severity
  • 7.5 (High) CVSS_V3 - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H CVSS Calculator
  • 7.5 (High) CVSS_V3 - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H CVSS Calculator
  • Ubuntu - medium
Summary
[none]
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.

References

Affected packages

Ubuntu:18.04:LTS

syncthing

Package

Name
syncthing
Purl
pkg:deb/ubuntu/syncthing@0.14.43+ds1-6?arch=source&distro=bionic

Affected ranges

Type
ECOSYSTEM
Events
Introduced
0Unknown introduced version / All previous versions are affected

Affected versions

0.*

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": "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"
        }
    ]
}

Ubuntu:20.04:LTS

syncthing

Package

Name
syncthing
Purl
pkg:deb/ubuntu/syncthing@1.1.4~ds1-4ubuntu1.2?arch=source&distro=focal

Affected ranges

Type
ECOSYSTEM
Events
Introduced
0Unknown introduced version / All previous versions are affected

Affected versions

1.*

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": "1.1.4~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"
        }
    ]
}

Ubuntu:25.04

syncthing

Package

Name
syncthing
Purl
pkg:deb/ubuntu/syncthing@1.29.2~ds1-1?arch=source&distro=plucky

Affected ranges

Type
ECOSYSTEM
Events
Introduced
0Unknown introduced version / All previous versions are affected

Affected versions

1.*

1.27.7~ds1-1
1.27.7~ds1-5
1.29.2~ds1-1

Ecosystem specific 

{
    "binaries": [
        {
            "binary_name": "golang-github-syncthing-syncthing-dev",
            "binary_version": "1.29.2~ds1-1"
        },
        {
            "binary_name": "syncthing",
            "binary_version": "1.29.2~ds1-1"
        },
        {
            "binary_name": "syncthing-discosrv",
            "binary_version": "1.29.2~ds1-1"
        },
        {
            "binary_name": "syncthing-relaysrv",
            "binary_version": "1.29.2~ds1-1"
        }
    ]
}

Ubuntu:25.10

syncthing

Package

Name
syncthing
Purl
pkg:deb/ubuntu/syncthing@1.29.5~ds1-2?arch=source&distro=questing

Affected ranges

Type
ECOSYSTEM
Events
Introduced
0Unknown introduced version / All previous versions are affected

Affected versions

1.*

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~ds1-2"
        },
        {
            "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"
        }
    ]
}

Ubuntu:Pro:22.04:LTS

syncthing

Package

Name
syncthing
Purl
pkg:deb/ubuntu/syncthing@1.18.0~ds1-3ubuntu0.3+esm1?arch=source&distro=esm-apps/jammy

Affected ranges

Type
ECOSYSTEM
Events
Introduced
0Unknown introduced version / All previous versions are affected

Affected versions

1.*

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

Ecosystem specific 

{
    "binaries": [
        {
            "binary_name": "golang-github-syncthing-syncthing-dev",
            "binary_version": "1.18.0~ds1-3ubuntu0.3+esm1"
        },
        {
            "binary_name": "syncthing",
            "binary_version": "1.18.0~ds1-3ubuntu0.3+esm1"
        },
        {
            "binary_name": "syncthing-discosrv",
            "binary_version": "1.18.0~ds1-3ubuntu0.3+esm1"
        },
        {
            "binary_name": "syncthing-relaysrv",
            "binary_version": "1.18.0~ds1-3ubuntu0.3+esm1"
        }
    ]
}

Ubuntu:Pro:24.04:LTS

syncthing

Package

Name
syncthing
Purl
pkg:deb/ubuntu/syncthing@1.27.2~ds4-1ubuntu0.24.04.3+esm1?arch=source&distro=esm-apps/noble

Affected ranges

Type
ECOSYSTEM
Events
Introduced
0Unknown introduced version / All previous versions are affected

Affected versions

1.*

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

Ecosystem specific 

{
    "binaries": [
        {
            "binary_name": "golang-github-syncthing-syncthing-dev",
            "binary_version": "1.27.2~ds4-1ubuntu0.24.04.3+esm1"
        },
        {
            "binary_name": "syncthing",
            "binary_version": "1.27.2~ds4-1ubuntu0.24.04.3+esm1"
        },
        {
            "binary_name": "syncthing-discosrv",
            "binary_version": "1.27.2~ds4-1ubuntu0.24.04.3+esm1"
        },
        {
            "binary_name": "syncthing-relaysrv",
            "binary_version": "1.27.2~ds4-1ubuntu0.24.04.3+esm1"
        }
    ]
}