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CVE-2020-26890

25
FAUCET Score

CVE-2020-26890 is a denial-of-service vulnerability affecting Matrix Synapse versions prior to 1.20.0, as well as related Fedora products. It arises from Synapse's improper handling of non-standard JSON values (NaN, Infinity, -Infinity) in m.room.member events. This vulnerability carries a CVSS score of 7.5 (High), indicating it can be exploited remotely with low attack complexity, leading to a complete denial of service. The impact is persistent, affecting both federation and Matrix clients, and requires manual event redaction to remediate. There is currently no evidence of active exploitation, nor are there known public exploits or Metasploit modules available. Community discussion and media coverage for this CVE are minimal.

Impacted Technologies

VendorProductVersion(s)CPE
< 1.20.0CPE matchmatch criteria
cpe:2.3:a:matrix:synapse:*:*:*:*:*:*:*:*
32CPE matchmatch criteria
cpe:2.3:o:fedoraproject:fedora:32:*:*:*:*:*:*:*
33CPE matchmatch criteria
cpe:2.3:o:fedoraproject:fedora:33:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.1

7.5HIGH

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

Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
NONE
Integrity Impact
NONE
Availability Impact
HIGH
Exploitability Score
3.9
Impact Score
3.6
CvssVersion
3.1

Exploit Intelligence

EPSS Score
2.97%
Probability of exploitation in next 30 days
EPSS Percentile
85.8%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
This CVE's current EPSS score of 0.0297 is in the 75th percentile among its peer group of 51,506 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.0 Reddit, 0.1 Bluesky, 0.1 Mastodon, and 0.4 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.1 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Patch Available

Vendor Patches (2)

github_advisorypatch availablevia nvd_reference
View patch
pippatch availablevia ghsa
Product: matrix-synapseFixed in: 1.20.0

Vendor Advisories (1)

pipGHSA-4mp3-385r-v63fhigh

Denial of service attack due to invalid JSON

Nov 24, 2020

References

github.com / matrix-org/synapse/security/advisories/GHSA-4mp3-385r-v63f
PatchThird Party Advisory
lists.fedoraproject.org / archives/list/package-announce%40lists.fedoraproject.org/message/G7YXMMYQP46PYL664JQUXCA3LPBJU7DQ
lists.fedoraproject.org / archives/list/package-announce%40lists.fedoraproject.org/message/U34DPP4ZLOEDUY2ZCWOHQPU5GA5LYNUQ