Improper input validation in Syncthing
CVE-2021-21404
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.
Vulnerability class: Drupalgeddon 2 (CVE-2018-7600)
EPSS: 0.020 (78.4th percentile) — read the EPSS interpretation.
CVSS v3 metric
CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.
Affected products
- Syncthing — versions < 1.15.0
Weakness classification (CWE)
Public proof-of-concept exploits
References
- security-advisories@github.com (x_refsource_CONFIRM, Third Party Advisory)
- security-advisories@github.com (Product, Third Party Advisory, x_refsource_MISC)
- security-advisories@github.com (Patch, Third Party Advisory, x_refsource_MISC)
- security-advisories@github.com (Third Party Advisory, x_refsource_MISC, Release Notes)
Frequently asked questions
- What is CVE-2021-21404?
- CVE-2021-21404 is a high-severity vulnerability in Syncthing, classified under Improper Input Validation. CVSS score: 7.5/10. Published 2021-04-06.
- How severe is CVE-2021-21404?
- High severity. CVSS v3 base score is 7.5 out of 10.
- Is CVE-2021-21404 known to be exploited?
- 1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.