# CVE-2023-42453: matrix-synapse vulnerable to improper validation of receipts allows forged read receipts

Source: https://junglewise.ai/threats/cve-2023-42453-matrix-synapse-vulnerable-to-improper-validation-of-receipts  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2023-09-27  
License: CC BY 4.0 with a link back

CVE-2023-42453 · Severity: low · CVSS 3.1 · Published 2023-09-27

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.

Technologies: [matrix-synapse (PyPI)](https://junglewise.ai/threats/technologies/matrix-synapse). Vendors: [PyPI](https://junglewise.ai/threats/vendors/pypi).

## Quick answers

**Is CVE-2023-42453 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2023-42453 being exploited in the wild.

**How severe is CVE-2023-42453?** Low severity, with a CVSS score of 3.1, published 27 September 2023.

**Which products and versions are affected?** matrix-synapse (PyPI) ECOSYSTEM:introduced=0.34.0,fixed=1.93.0, ECOSYSTEM:introduced=1.34.0,fixed=1.93.0.

**Is there a fix for CVE-2023-42453?** Yes. matrix-synapse (PyPI): upgrade to 1.93.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**Am I affected by CVE-2023-42453?** Check whether you run matrix-synapse (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- matrix-synapse (PyPI): upgrade to 1.93.0 or later

  ```sh
  pip install "matrix-synapse>=1.93.0"
  ```


## Affected products

- matrix-synapse (PyPI) ECOSYSTEM:introduced=0.34.0,fixed=1.93.0, ECOSYSTEM:introduced=1.34.0,fixed=1.93.0

## Identifiers

- CVE-2023-42453
- GHSA-7565-cq32-vx2x
- PYSEC-2023-180

## Related threats

- [PYSEC-2026-2620 - matrix-sydent and matrix-synapse Use Cryptographically Weak PRNG](https://junglewise.ai/threats/cve-2019-11842-matrix-sydent-and-matrix-synapse-use-cryptographically-weak-prng)
- [PYSEC-2026-1614 - Synapse vulnerable to federation denial of service via malformed events](https://junglewise.ai/threats/cve-2025-30355-synapse-vulnerable-to-federation-denial-of-service-via-malformed)
- [PYSEC-2026-1610 - Synapse Matrix has a partial room state leak via Sliding Sync](https://junglewise.ai/threats/cve-2024-53867-synapse-matrix-has-a-partial-room-state-leak-via-sliding-sync)
- [Synapse can be forced to thumbnail unexpected file formats, invoking external, potentially untrustworthy decoders](https://junglewise.ai/threats/cve-2024-53863-synapse-can-be-forced-to-thumbnail-unexpected-file-formats)
- [PYSEC-2026-1611 - Synapse allows a a malformed invite to break the invitee's `/sync`](https://junglewise.ai/threats/cve-2024-52815-synapse-allows-a-a-malformed-invite-to-break-the-invitee-s-sync)