vulntracker.iovulntracker.io
© 2026 vulntracker.io

CVE-2021-40823

MEDIUM
5.9
CVSS Score
Published: September 13, 2021 at 06:45 PM UTC
Updated: June 17, 2026 at 04:07 AM UTC
1 product affected across 1 vendorJavaScript SDK

Using N/A by N/A?

Get instant alerts when new vulnerabilities affect N/A - before attackers find them.

Real-time alertsTrack your software stackFree plan available
Start FreeSign In
Severity
MEDIUM5.9
Exploit prediction
EPSS 0.7%

Description

A logic error in the room key sharing functionality of matrix-js-sdk (aka Matrix Javascript SDK) before 12.4.1 allows a malicious Matrix homeserver present in an encrypted room to steal room encryption keys (via crafted Matrix protocol messages) that were originally sent by affected Matrix clients participating in that room. This allows the homeserver to decrypt end-to-end encrypted messages sent by affected clients.

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

JavaScript SDK· Matrixnpm
95%
v < 12.4.1
Affected range stops below 12.4.1, so it looks safe — our inference, not a vendor statement

Remediation

No guide yet

No remediation guidance has been written for this CVE yet. What the record does show:

Patch and advisory references

References (2)

x_refsource_MISCThird Party Advisory
Source: [email protected]
https://github.com/matrix-org/matrix-js-sdk/releases/tag/v12.4.1
x_refsource_MISCVendor Advisory
Source: [email protected]
https://matrix.org/blog/2021/09/13/vulnerability-disclosure-key-sharing

CVSS

5.9MEDIUM[email protected]
Attack Vector
NETWORK
Complexity
HIGH
Privileges
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality
HIGH
Integrity
NONE
Availability
NONE
Vector?

Quick Info

StatusMODIFIED
CWE
CWE-290

Get alerted

Stop reading CVE feeds looking for your own stack

Track the products you run and VulnTracker tells you when a new CVE affects them — with what is known about fixing it, and nothing about the rest.

Create accountSign in
Free plan, no card