Is CVE-2021-21333 in the CISA KEV catalog?

No. CVE-2021-21333 is not currently on the CISA Known Exploited Vulnerabilities list.

What is the CVSS severity of CVE-2021-21333?

CVE-2021-21333 has a CVSS v3 base score of 6.1 (MEDIUM).

What is the EPSS score for CVE-2021-21333?

CVE-2021-21333 has an EPSS score of 1.39% (69th percentile), estimating the probability of exploitation in the next 30 days.

How do I fix CVE-2021-21333?

Upgrade matrix-synapse on debian unstable to 1.27.0-1 or later.

CVE & CISA-KEV Catalog

CVE-2021-21333

MEDIUM

6.1

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 1.27.0, the notification emails sent for notifications for missed messages or for an expiring account are subject to HTML injection. In the case of the notification for missed messages, this could allow an attacker to insert forged content into the email. The account expiry feature is not enabled by default and the HTML injection is not controllable by an attacker. This is fixed in version 1.27.0.

CWE-74Injection CWE-79Cross-Site Scripting (XSS)

How to fix

Remediation Available

matrix-synapseDebian

Fixed in:1.27.0-1CVE-2021-21333

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 RequiredNone

User InteractionRequired

ScopeChanged

Impact

ConfidentialityNone

IntegrityHigh

AvailabilityNone

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

Exploit Intelligence

1.39%probability of exploitation in 30 days

69thpercentile

Moderate risk: more likely to be exploited than 69% of all known CVEs.

References

Patch3

Third-Party Advisory1

github.com

Other references1

lists.fedoraproject.org

Related Vulnerabilities

Other CWE-74 (Injection) vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2013-2251	Critical	9.8	100%	KEV	Fix
CVE-2023-22527	Critical	9.8	100%	KEV + Ransom	Fix
CVE-2019-2725	Critical	9.8	100%	KEV + Ransom	Fix
CVE-2022-46169	Critical	9.8	100%	KEV	Fix
CVE-2022-35914	Critical	9.8	100%	KEV	-
CVE-2019-17558	High	7.5	99%	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.