How severe is CVE-2023-43796?

CVE-2023-43796 has a CVSS score of 5.3/10, rated MEDIUM. Review your exposure and patch according to your risk tolerance.

Which packages are affected by CVE-2023-43796?

CVE-2023-43796 affects the following packages: matrix-synapse (PyPI). Ecosystems affected: PyPI.

How do I fix CVE-2023-43796?

Update matrix-synapse to 1.95.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2023-43796 is resolved across your whole dependency graph.

How do I detect CVE-2023-43796 in my PyPI dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for matrix-synapse, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2023-43796 if there is no patch (or I can't update yet)?

Assume what was exposed is already known: rotate any credential, token or key that the affected component could return, restrict the endpoint to callers that genuinely need it, and strip sensitive fields from responses and error output at the boundary rather than relying on the client not to read them.

Is CVE-2023-43796 actively exploited in the wild?

No public exploit code has been indexed for CVE-2023-43796 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2023-43796?

CVE-2023-43796 has an EPSS (Exploit Prediction Scoring System) score of 1.2%, placing it in the 68th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2023-43796?

CVE-2023-43796 is classified as Information Exposure (CWE-200). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2023-43796 published, and has it been updated?

CVE-2023-43796 was published on October 31, 2023 and was last updated on October 28, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐍

🐍 PyPI

Not in CISA KEV

MEDIUM severity

CVE-2023-43796 — matrix-synapse

MEDIUMFix: matrix-org/synapse@daec55e

CVE-2023-43796 is a medium-severity (CVSS 5.3) Information Exposure vulnerability in matrix-synapse. A fix is available for matrix-synapse — see the affected versions and patch details below.

Synapse vulnerable to leak of remote user device information

Also known asGHSA-mp92-3jfm-3575PYSEC-2023-230

Published

Oct 31, 2023

Updated

Oct 28, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Nov 7, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗

1.2%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs68th percentile — riskier than 68% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

1 pkg affected

🐍matrix-synapse

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.

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.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐍PyPI	`matrix-synapse`	all versions	1.95.1`pip install --upgrade 'matrix-synapse==1.95.1'`

Affected Products

2 products · 3 configurations

fedorafedoraproject

2 versions

3839

Application

synapsematrix

< 1.95.1

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for matrix-synapse, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update matrix-synapse to 1.95.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2023-43796 is resolved across your whole dependency graph.
Workarounds
Assume what was exposed is already known: rotate any credential, token or key that the affected component could return, restrict the endpoint to callers that genuinely need it, and strip sensitive fields from responses and error output at the boundary rather than relying on the client not to read them.

Frequently Asked Questions

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.

O3 Security · Impact-Aware SCA

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