# CVE-2023-42453: Improper validation of receipts allows forged read receipts in matrix synapse

> Attackers can forge read receipts for any event in Matrix Synapse, misleading clients about user activity without viewing the content.

- **Severity:** Low 3.1 (`CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 26 Sep 2023
- **Updated:** 18 Jun 2025
- **Also known as:** GHSA-7565-cq32-vx2x, PYSEC-2023-180, UBUNTU-CVE-2023-42453

## What is CVE-2023-42453?

CVE-2023-42453 is a low-severity vulnerability in Fedoraproject Fedora, published on 26 Sep 2023. Any signed-in user can exploit it over the network, with no action from the victim.

### Official 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.

Weakness: CWE-285 (Improper Authorization)

## Which versions are affected by CVE-2023-42453?

3 open source packages ship an affected version, including matrix-synapse. It affects 2 products.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `matrix-synapse` | PyPI | From 0.34.0 | 1.93.0 |
| `matrix-synapse` | PyPI | From 0.34.0 | 1.93.0 |
| `matrix-synapse` | PyPI | From 1.34.0 | 1.93.0 |

Products: Fedoraproject Fedora, Matrix Synapse.

## How do I fix CVE-2023-42453?

Upgrade matrix-synapse to 1.93.0 or later.

## Is CVE-2023-42453 being exploited?

There is no known exploitation of CVE-2023-42453 in the wild and no public exploit code.

## Other vulnerabilities in Fedoraproject Fedora

- [CVE-2024-4577](https://insights.sbomify.com/CVE-2024-4577/): PHP-CGI OS Command Injection (critical 9.8, exploited in the wild)
- [CVE-2021-39226](https://insights.sbomify.com/CVE-2021-39226/): Grafana Authentication Bypass (critical 9.8, exploited in the wild)
- [CVE-2019-5544](https://insights.sbomify.com/CVE-2019-5544/): VMware ESXi and Horizon DaaS OpenSLP Heap-Based Buffer Overflow (critical 9.8, exploited in the wild)
- [CVE-2024-4947](https://insights.sbomify.com/CVE-2024-4947/): Google Chromium V8 Type Confusion (critical 9.6, exploited in the wild)
- [CVE-2024-4671](https://insights.sbomify.com/CVE-2024-4671/): Google Chromium Visuals Use-After-Free (critical 9.6, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2023-42453 and fix it if it is affected.

What it is: CVE-2023-42453 is a low-severity vulnerability in Fedoraproject Fedora, published on 26 Sep 2023. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2023-42453 in the wild and no public exploit code.

Affected packages and fixed versions:
- matrix-synapse (PyPI): affected from 0.34.0; fixed in 1.93.0
- matrix-synapse (PyPI): affected from 0.34.0; fixed in 1.93.0
- matrix-synapse (PyPI): affected from 1.34.0; fixed in 1.93.0

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2023-42453/ (Markdown: https://insights.sbomify.com/CVE-2023-42453/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2023-42453
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2023-42453
- OSV: https://osv.dev/vulnerability/CVE-2023-42453

---
From sbomify Insights: https://insights.sbomify.com/CVE-2023-42453/
Summaries are generated and may contain mistakes; the official description above is the record.