CVE-2023-32683: URL deny list bypass via oEmbed and image URLs when generating previews in Synapse
First published: Tue Jun 06 2023(Updated: )
### 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.
Credit: security-advisories@github.com security-advisories@github.com
| Affected Software | Affected Version | How to fix |
|---|---|---|
| Matrix Synapse | <1.85.0 | |
| pip/matrix-synapse | <1.85.0 | 1.85.0 |
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Reference Links
- https://github.com/matrix-org/synapse/pull/15601
- https://github.com/matrix-org/synapse/security/advisories/GHSA-98px-6486-j7qc
- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/X6DH5A5YEB5LRIPP32OUW25FCGZFCZU2/
- https://github.com/matrix-org/synapse/releases/tag/v1.85.0
- https://nvd.nist.gov/vuln/detail/CVE-2023-32683
- https://github.com/pypa/advisory-database/tree/main/vulns/matrix-synapse/PYSEC-2023-85.yaml
- https://github.com/advisories/GHSA-98px-6486-j7qc (Advisory)
- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/X6DH5A5YEB5LRIPP32OUW25FCGZFCZU2
Frequently Asked Questions
What is CVE-2023-32683?
CVE-2023-32683 is a vulnerability in Synapse, a Matrix protocol homeserver, that allows bypassing network policies and potentially enables server-side request forgery.
What is the impact of CVE-2023-32683?
The impact of CVE-2023-32683 is limited to IP addresses allowed by the 'url_preview_url_blacklist' setting in Synapse.
How can CVE-2023-32683 be exploited?
CVE-2023-32683 can be exploited by using a discovered oEmbed or image URL to bypass the 'url_preview_url_blacklist' setting in Synapse, potentially leading to server-side request forgery or bypassing network policies.
How can I fix CVE-2023-32683?
To fix CVE-2023-32683, update your Synapse installation to version 1.85.0 or above.
Where can I find more information about CVE-2023-32683?
You can find more information about CVE-2023-32683 in the GitHub pull request and security advisory, as well as the Fedora Project mailing list.
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