Synapse has URL deny list bypass via oEmbed and image URLs when generating previews
Impact
A discovered oEmbed or image URL can bypass the url_preview_url_blacklist setting potentially allowing server side request forgery or bypassing network policies. Impact is limited to IP addresses allowed by the url_preview_ip_range_blacklist setting (by default this only allows public IPs) and by the limited information returned to the client:
- For discovered oEmbed URLs, any non-JSON response or a JSON response which includes non-oEmbed information is discarded.
- For discovered image URLs, any non-image response is discarded.
Systems which have URL preview disabled (via the url_preview_enabled setting) or have not configured a url_preview_url_blacklist are not affected.
Because of the uncommon configuration required, the limited information a malicious user, and the amount of guesses/time the attack would need; the severity is rated as low.
Patches
The issue is fixed by #15601.
Workarounds
The default configuration of the url_preview_ip_range_blacklist should protect against requests being made to internal infrastructure, URL previews of public URLs is expected.
Alternately URL previews could be disabled using the url_preview_enabled setting.
Affected software
Click a technology to see all vulnerabilities affecting it.
| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Python (PyPI) | matrix-synapse | < 1.85.0 | 1.85.0 |
References
- https://github.com/matrix-org/synapse/security/advisories/GHSA-98px-6486-j7qc
- https://github.com/matrix-org/synapse/pull/15601
- https://nvd.nist.gov/vuln/detail/CVE-2023-32683
- https://github.com/matrix-org/synapse
- https://github.com/matrix-org/synapse/releases/tag/v1.85.0
- https://github.com/pypa/advisory-database/tree/main/vulns/matrix-synapse/PYSEC-2023-85.yaml
- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/X6DH5A5YEB5LRIPP32OUW25FCGZFCZU2
- CVSS vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:N/I:L/A:N- Weakness (CWE)
CWE-863, CWE-918- Platform
- Python (PyPI)
- Package
matrix-synapse- Disclosed
- 06.06.2023
- Updated
- 11.10.2026 11:20
Sources and licenses
OSV / GitHub Advisory Database - PYSEC-2023-85 - PyPA Advisory Database; CC BY 4.0
OSV / GitHub Advisory Database - GHSA-98px-6486-j7qc - CC BY 4.0
Vulnerability history: matrix-synapse
All published vulnerabilities of this package (Python (PyPI)), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 45
- First → latest
- 03.2019 05.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- High 21
- Medium 21
- Low 3
Disclosures per year
- 2019: 3
- 2020: 3
- 2021: 12
- 2022: 7
- 2023: 9
- 2024: 7
- 2025: 2
- 2026: 2
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Synapse has URL deny list bypass via oEmbed and image URLs when generating previews this entry
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