Is CVE-2020-26257 in the CISA KEV catalog?

No. CVE-2020-26257 is not currently on the CISA Known Exploited Vulnerabilities list.

What is the CVSS severity of CVE-2020-26257?

CVE-2020-26257 has a CVSS v3 base score of 6.5 (MEDIUM).

What is the EPSS score for CVE-2020-26257?

CVE-2020-26257 has an EPSS score of 2.36% (82th percentile), estimating the probability of exploitation in the next 30 days.

How do I fix CVE-2020-26257?

Upgrade matrix-synapse on debian unstable to 1.24.0-1 or later.

CVE & CISA-KEV Catalog

CVE-2020-26257

MEDIUMEPSS 82th pctl

6.5

CVSS v3

NVD

Description

Matrix is an ecosystem for open federated Instant Messaging and VoIP. Synapse is a reference "homeserver" implementation of Matrix. A malicious or poorly-implemented homeserver can inject malformed events into a room by specifying a different room id in the path of a `/send_join`, `/send_leave`, `/invite` or `/exchange_third_party_invite` request. This can lead to a denial of service in which future events will not be correctly sent to other servers over federation. This affects any server which accepts federation requests from untrusted servers. The Matrix Synapse reference implementation before version 1.23.1 the implementation is vulnerable to this injection attack. Issue is fixed in version 1.23.1. As a workaround homeserver administrators could limit access to the federation API to trusted servers (for example via `federation_domain_whitelist`).

CWE-79Cross-Site Scripting (XSS)CWE-400Resource Exhaustion

How to fix

Remediation Available

matrix-synapseDebian

Fixed in:1.24.0-1CVE-2020-26257

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 RequiredLow

User InteractionNone

ScopeUnchanged

Impact

ConfidentialityNone

IntegrityNone

AvailabilityHigh

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

Exploit Intelligence

2.36%probability of exploitation in 30 days

82ndpercentile

Elevated risk: more likely to be exploited than 82% of all known CVEs.

References

Patch2

Third-Party Advisory2

Other references2

Related Vulnerabilities

Other CWE-79 (Cross-Site Scripting (XSS)) vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2020-11022	Medium	6.9	99%	-	Fix
CVE-2019-3929	Critical	9.8	99%	KEV	Fix
CVE-2020-9496	Medium	6.1	99%	-	-
CVE-2023-28341	Medium	6.1	99%	-	Fix
CVE-2018-12998	Medium	6.1	98%	-	-
CVE-2025-4123	High	7.6	98%	-	Fix

Embed a live status badge for CVE-2020-26257

Markdown

[![CVE-2020-26257](https://tridentstack.com/cve/badge/CVE-2020-26257.svg)](https://tridentstack.com/cve/CVE-2020-26257)

HTML

<a href="https://tridentstack.com/cve/CVE-2020-26257"><img src="https://tridentstack.com/cve/badge/CVE-2020-26257.svg" alt="CVE-2020-26257"></a>

Find and fix vulnerabilities across your fleet

TridentStack Control continuously scans your Windows, macOS, and Linux fleet for known vulnerabilities, prioritizes them by severity and active exploitation, and patches them automatically.

Start free

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.