CVE-2021-21404
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.
Does this matter?
High impact if exploited, but EPSS currently rates exploitation as unlikely (1.97%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.
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.
- CVSS 3.1
- 7.5 HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- EPSS
- 1.97% probability · 79th percentile
- CISA KEV
- Not listed
- Weakness
- CWE-20
- Affected
- syncthing/syncthing
- Source
- security-advisories@github.com
References
- https://github.com/syncthing/syncthing/commit/fb4fdaf4c0a79c22cad000c42ac1394e3ccb6a97Patch, Third Party Advisory
- https://github.com/syncthing/syncthing/releases/tag/v1.15.0Release Notes, Third Party Advisory
- https://github.com/syncthing/syncthing/security/advisories/GHSA-x462-89pf-6r5hThird Party Advisory
- https://pkg.go.dev/github.com/syncthing/syncthingProduct, Third Party Advisory
- https://github.com/syncthing/syncthing/commit/fb4fdaf4c0a79c22cad000c42ac1394e3ccb6a97Patch, Third Party Advisory
- https://github.com/syncthing/syncthing/releases/tag/v1.15.0Release Notes, Third Party Advisory
- https://github.com/syncthing/syncthing/security/advisories/GHSA-x462-89pf-6r5hThird Party Advisory
- https://pkg.go.dev/github.com/syncthing/syncthingProduct, Third Party Advisory
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.