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CVE-2019-18835

30
FAUCET Score

CVE-2019-18835 is a critical vulnerability affecting Matrix Synapse versions prior to 1.5.0, where the software improperly validates signatures on federation APIs for /send_join, /send_leave, and /invite events. This allows for the potential acceptance of unsigned or spoofed events from unexpected servers. With a CVSS score of 9.8 (Critical), it presents a high-impact, low-complexity remote attack vector, leading to potential complete compromise of confidentiality, integrity, and availability. While there is no evidence of active exploitation, nor publicly available exploit code in common databases, the vulnerability has garnered significant community discussion, indicating awareness within the security community.

Impacted Technologies

VendorProductVersion(s)CPE
< 1.5.0CPE matchmatch criteria
cpe:2.3:a:matrix:synapse:*:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.1

9.8CRITICAL

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

Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
HIGH
Integrity Impact
HIGH
Availability Impact
HIGH
Exploitability Score
3.9
Impact Score
5.9
CvssVersion
3.1

Exploit Intelligence

EPSS Score
0.86%
Probability of exploitation in next 30 days
EPSS Percentile
54.8%
Percentile rank of EPSS score among Peer Group
As of 2026-07-25
Model: v2026.06.15
This CVE's current EPSS score of 0.0086 is in the 39th percentile among its peer group of 36,833 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.1 Reddit, 0.3 Bluesky, 0.3 Mastodon, and 2.4 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.3 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: 1.5.0

Vendor Advisories (1)

pipGHSA-cppw-2mf8-qpm5high

Improper Verification of Cryptographic Signature in matrix-synapse

May 24, 2022

References

github.com / matrix-org/synapse/pull/6262
PatchThird Party Advisory
github.com / matrix-org/synapse/releases/tag/v1.5.0
Release NotesThird Party Advisory