CVE-2021-21404
7.5 · HIGHOverview
CVE-2021-21404 is a high-severity vulnerability affecting syncthing syncthing. It was published on April 6, 2021 and has a CVSS 3.1 base score of 7.5 (HIGH).
This vulnerability has a CVSS 3.1 base score of 7.5, rated HIGH. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.
Technical 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.
Remediation
Check the references section for vendor advisories and patches from syncthing. Update syncthing to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.
Affected Products
| Vendor | Product | Versions | Status |
|---|---|---|---|
| syncthing | syncthing | >= 0, < 1.15.0 | Affected |
References
Frequently Asked Questions
What is CVE-2021-21404?
CVE-2021-21404 is a high-severity vulnerability affecting syncthing syncthing. It was published on April 6, 2021 and has a CVSS 3.1 base score of 7.5 (HIGH).
How severe is CVE-2021-21404?
This vulnerability has a CVSS 3.1 base score of 7.5, rated HIGH. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.
How do I fix or remediate CVE-2021-21404?
Check the references section for vendor advisories and patches from syncthing. Update syncthing to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.
How can CyberStrike help with CVE-2021-21404?
CyberStrike's AI-powered security agents can automatically detect CVE-2021-21404 across your infrastructure using autonomous pentesting, DAST scanning, and HackBrowser. The platform continuously monitors for known vulnerabilities and provides actionable remediation guidance prioritized by real-world exploitability.
How CyberStrike Helps
AI agents map your attack surface to find vulnerabilities like this one.
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