CVE-2023-42453

What it is

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.

At a glance

Exploitability

Can be exploited over the network with a low-privilege account. Limited direct impact.

Exploit odds

0.8% chance of exploitation in the next 30 days (EPSS).

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2023-09-27 15:19 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-06-17 06:23 UTC Last updatedMost recent change to the record

Why it ranks here

• Exploited in the wild: no, CISA does not list it.
• Exploit odds: 0.8% in the next 30 days (EPSS).
• Severity: 3.1 LOW (CVSS).
• Fix: a patch or advisory is linked.

Details

Published

2023-09-27 15:19 UTC

Last modified

2026-06-17 06:23 UTC

Exploit probability

0.8% · EPSS, next 30 days

Weakness

CWE-285

Record status

Modified

Affected

• Matrix Synapse < 1.93.0
• Fedoraproject Fedora 37
• Fedoraproject Fedora 38

Attack profile CVSS 3.1 · 3.1

Attack vector

Network

Complexity

High

Privileges needed

Low

User interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

Low

Availability

None

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2023-42453.md and follow it. Check whether this project is affected by CVE-2023-42453. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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