Is CVE-2021-21393 in the CISA KEV catalog?

No. CVE-2021-21393 is not currently on the CISA Known Exploited Vulnerabilities list.

What is the CVSS severity of CVE-2021-21393?

CVE-2021-21393 has a CVSS v3 base score of 5.3 (MEDIUM).

What is the EPSS score for CVE-2021-21393?

CVE-2021-21393 has an EPSS score of 1.60% (73th percentile), estimating the probability of exploitation in the next 30 days.

How do I fix CVE-2021-21393?

Upgrade matrix-synapse on debian unstable to 1.28.0-1 or later.

CVE & CISA-KEV Catalog

CVE-2021-21393

MEDIUMEPSS 73th pctl

5.3

CVSS v3

NVD

Description

Synapse is a Matrix reference homeserver written in python (pypi package matrix-synapse). Matrix is an ecosystem for open federated Instant Messaging and VoIP. In Synapse before version 1.28.0 Synapse is missing input validation of some parameters on the endpoints used to confirm third-party identifiers could cause excessive use of disk space and memory leading to resource exhaustion. Note that the groups feature is not part of the Matrix specification and the chosen maximum lengths are arbitrary. Not all clients might abide by them. Refer to referenced GitHub security advisory for additional details including workarounds.

CWE-20Improper Input Validation

How to fix

Remediation Available

matrix-synapseDebian

Fixed in:1.28.0-1CVE-2021-21393

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 ComplexityHigh

Privileges RequiredLow

User InteractionNone

ScopeUnchanged

Impact

ConfidentialityNone

IntegrityNone

AvailabilityHigh

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

Exploit Intelligence

1.60%probability of exploitation in 30 days

73rdpercentile

Elevated risk: more likely to be exploited than 73% of all known CVEs.

References

Patch3

Third-Party Advisory1

pypi.org

Other references1

lists.fedoraproject.org

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.