CVE-2023-42453

Improper validation of receipts allows forged read receipts in matrix synapse

MEDIUM
4.3
CVSS Score
Published: September 26, 2023 at 08:49 PM UTC
Updated: June 17, 2026 at 06:23 AM UTC
3 products affected across 3 vendorsFedoraSynapseSynapse

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Severity
MEDIUM4.3
Exploit prediction
EPSS 0.8%
SSVC
No known exploit

Description

Synapse is an open-source Matrix homeserver written and maintained by the Matrix.org Foundation. Users were able to forge read receipts for any event (if they knew the room ID and event ID). Note that the users were not able to view the events, but simply mark it as read. This could be confusing as clients will show the event as read by the user, even if they are not in the room. This issue has been patched in version 1.93.0. Users are advised to upgrade. There are no known workarounds for this issue.

Affected

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

1.34.0 ≤ v < 1.93.0
Affected range stops below 1.93.0, so it looks safe — our inference, not a vendor statement
v < 1.93.0
Affected range stops below 1.93.0, 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:

SSVC — Action Prioritization

SSVCNo known exploitNot automatablePartial impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

Attack Vector
NETWORK
Complexity
LOW
Privileges
LOW
User Interaction
NONE
Scope
UNCHANGED
Confidentiality
NONE
Integrity
LOW
Availability
NONE
Vector?

Quick Info

StatusMODIFIED
CWE
CWE-285NVD-CWE-Other

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