Is CVE-2021-21404 in the CISA KEV catalog?

No. CVE-2021-21404 is not currently on the CISA Known Exploited Vulnerabilities list.

What is the CVSS severity of CVE-2021-21404?

CVE-2021-21404 has a CVSS v3 base score of 7.5 (HIGH).

What is the EPSS score for CVE-2021-21404?

CVE-2021-21404 has an EPSS score of 1.97% (78th percentile), estimating the probability of exploitation in the next 30 days.

How do I fix CVE-2021-21404?

Upgrade syncthing on debian 11 to 1.12.1~ds1-3 or later. Fixes are available for 3 affected products.

CVE & CISA-KEV Catalog

CVE-2021-21404

HIGHEPSS 78th pctl

7.5

CVSS v3

NVD

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.

CWE-20Improper Input Validation

How to fix

Remediation Available

syncthingDebian

Fixed in:1.12.1~ds1-3CVE-2021-21404

SyncTrayzorWindows application

Affected:1.15.0Fixed in:1.15.0SyncTrayzor

SyncthingWindows application

Affected:1.15.0Fixed in:1.15.0The Syncthing Authors

Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.

CVSS v3 Vector

Exploitability

Attack VectorNetwork

Attack ComplexityLow

Privileges RequiredNone

User InteractionNone

ScopeUnchanged

Impact

ConfidentialityNone

IntegrityNone

AvailabilityHigh

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Exploit Intelligence

1.97%probability of exploitation in 30 days

78thpercentile

Elevated risk: more likely to be exploited than 78% of all known CVEs.

References

Patch1

github.com

Third-Party Advisory3

Related Vulnerabilities

Other CWE-20 (Improper Input Validation) vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2024-3400	Critical	10.0	100%	KEV + Ransom	-
CVE-2021-45105	Medium	5.9	100%	-	Fix
CVE-2021-44228	Critical	10.0	100%	KEV + Ransom	Fix
CVE-2021-21985	Critical	9.8	100%	KEV + Ransom	Fix
CVE-2018-7600	Critical	9.8	100%	KEV + Ransom	Fix
CVE-2020-3452	High	7.5	100%	KEV	Fix

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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2024-11-21.