CVE-2021-40824

MEDIUM
5.9
CVSS Score
Published: September 13, 2021 at 06:49 PM UTC
Updated: June 17, 2026 at 04:07 AM UTC
2 products affected across 1 vendorElementMatrix Android SDK2

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Severity
MEDIUM5.9
Exploit prediction
EPSS 0.7%

Description

A logic error in the room key sharing functionality of Element Android before 1.2.2 and matrix-android-sdk2 (aka Matrix SDK for Android) before 1.2.2 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 attacker 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.

v < 1.2.2
Affected range stops below 1.2.2, so it looks safe — our inference, not a vendor statement
v < 1.2.2
Affected range stops below 1.2.2, 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:

CVSS

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

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