CVE-2021-21404
Crash due to malformed relay protocol message
Description
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.
How to fix CVE-2021-21404
To remediate CVE-2021-21404, upgrade the affected package to a fixed version below.
- —upgrade to 1.15.0 or later
- —upgrade to 1.12.1~ds1-3 or later
- —upgrade to 1.15.0 or later
- —upgrade to 1.15.0 or later
Is CVE-2021-21404 being exploited?
Low — EPSS is 0.3%, meaning exploitation activity has not been observed at scale.
Affected packages (4)
- from 0, < 1.15.0
- from 0, < 1.12.1~ds1-3
- from 0, < 1.15.0
- from 0, < 1.15.0
CVSS scores
| Source | Version | Severity | Vector |
|---|---|---|---|
| osv | CVSS 3.1 | HIGH7.5 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H |