Is CVE-2021-21274 in the CISA KEV catalog?

No. CVE-2021-21274 is not currently on the CISA Known Exploited Vulnerabilities list.

What is the CVSS severity of CVE-2021-21274?

CVE-2021-21274 has a CVSS v3 base score of 4.3 (MEDIUM).

What is the EPSS score for CVE-2021-21274?

CVE-2021-21274 has an EPSS score of 2.16% (80th percentile), estimating the probability of exploitation in the next 30 days.

How do I fix CVE-2021-21274?

Upgrade matrix-synapse on debian unstable to 1.25.0-1 or later.

CVE & CISA-KEV Catalog

CVE-2021-21274

MEDIUMEPSS 80th pctl

4.3

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 1.25.0, a malicious homeserver could redirect requests to their .well-known file to a large file. This can lead to a denial of service attack where homeservers will consume significantly more resources when requesting the .well-known file of a malicious homeserver. This affects any server which accepts federation requests from untrusted servers. Issue is resolved in version 1.25.0. As a workaround the `federation_domain_whitelist` setting can be used to restrict the homeservers communicated with over federation.

CWE-400Resource Exhaustion CWE-770Allocation of Resources Without Limits or Throttling

How to fix

Remediation Available

matrix-synapseDebian

Fixed in:1.25.0-1CVE-2021-21274

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 InteractionRequired

ScopeUnchanged

Impact

ConfidentialityNone

IntegrityNone

AvailabilityLow

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

Exploit Intelligence

2.16%probability of exploitation in 30 days

80thpercentile

Elevated risk: more likely to be exploited than 80% of all known CVEs.

References

Patch3

Third-Party Advisory1

github.com

Other references1

lists.fedoraproject.org

Related Vulnerabilities

Other CWE-400 (Resource Exhaustion) vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2023-44487	High	7.5	100%	KEV	Fix
CVE-2021-44228	Critical	10.0	100%	KEV + Ransom	Fix
CVE-2011-3192	High	7.8	99%	-	Fix
CVE-2019-11478	Medium	5.3	95%	-	Fix
CVE-2024-25617	Medium	5.3	89%	-	Fix
CVE-2018-1000115	High	7.5	89%	-	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.