# CVE-2023-43796: Synapse vulnerable to leak of remote user device information

> Attackers can enumerate remote users known to a Synapse homeserver by querying cached device information, exposing user metadata.

- **Severity:** Medium 5.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 31 Oct 2023
- **Updated:** 13 Feb 2025
- **Also known as:** GHSA-mp92-3jfm-3575, PYSEC-2023-230, UBUNTU-CVE-2023-43796, openSUSE-SU-2024:13392-1

## What is CVE-2023-43796?

CVE-2023-43796 is a medium-severity vulnerability in Fedoraproject Fedora, published on 31 Oct 2023. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Synapse is an open-source Matrix homeserver Prior to versions 1.95.1 and 1.96.0rc1, cached device information of remote users can be queried from Synapse. This can be used to enumerate the remote users known to a homeserver. System administrators are encouraged to upgrade to Synapse 1.95.1 or 1.96.0rc1 to receive a patch. As a workaround, the `federation_domain_whitelist` can be used to limit federation traffic with a homeserver.

Weakness: CWE-200 (Exposure of Sensitive Information to an Unauthorized Actor)

## Which versions are affected by CVE-2023-43796?

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


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `matrix-synapse` | PyPI | All versions | 1.95.1 |
| `matrix-synapse` | PyPI | All versions | 1.95.1 |
| `matrix-synapse` | PyPI | All versions | 1.95.1 |
| `matrix-synapse` | openSUSE:Tumbleweed | All versions | 1.95.1-1.1 |

Products: Fedoraproject Fedora, Matrix Synapse.

## How do I fix CVE-2023-43796?

Upgrade matrix-synapse to 1.95.1 or later.

## Is CVE-2023-43796 being exploited?

There is no known exploitation of CVE-2023-43796 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-2023-43796 and fix it if it is affected.

What it is: CVE-2023-43796 is a medium-severity vulnerability in Fedoraproject Fedora, published on 31 Oct 2023. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2023-43796 in the wild and no public exploit code.

Affected packages and fixed versions:
- matrix-synapse (PyPI): affected all versions; fixed in 1.95.1
- matrix-synapse (PyPI): affected all versions; fixed in 1.95.1
- matrix-synapse (PyPI): affected all versions; fixed in 1.95.1

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-2023-43796/ (Markdown: https://insights.sbomify.com/CVE-2023-43796/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2023-43796
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2023-43796
- OSV: https://osv.dev/vulnerability/CVE-2023-43796

---
From sbomify Insights: https://insights.sbomify.com/CVE-2023-43796/
Summaries are generated and may contain mistakes; the official description above is the record.