CVE-2023-32683 URL deny list bypass via oEmbed and image URLs when generating previews in Synapse
Attackers can bypass URL blacklists via oEmbed or image previews in Synapse, enabling server-side request forgery against allowed IP ranges.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2023-32683?
CVE-2023-32683 is a low-severity server-side request forgery vulnerability in matrix-org synapse, published on 6 Jun 2023. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.
Official description
Synapse is a Matrix protocol homeserver written in Python with the Twisted framework. 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: 1. For discovered oEmbed URLs, any non-JSON response or a JSON response which includes non-oEmbed information is discarded. 2. 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. This issue has been addressed in version 1.85.0. Users are advised to upgrade. User unable to upgrade may also disable URL previews.
Which versions are affected by CVE-2023-32683?
3 open source packages ship an affected version, including matrix-synapse. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
matrix-synapse PyPI | All versions | 1.85.0 |
matrix-synapse PyPI | All versions | 1.85.0 |
matrix-synapse PyPI | All versions | 1.85.0 |
Products include Matrix Synapse.
How do I fix CVE-2023-32683?
Upgrade matrix-synapse to 1.85.0 or later.
Upgrade, and send outbound requests through an allow-list that blocks internal addresses. More about Server-side request forgery.
Is CVE-2023-32683 being exploited?
There is no known exploitation of CVE-2023-32683 in the wild and no public exploit code.
Other vulnerabilities in matrix-org synapse
- CVE-2019-18835 Improper Verification of Cryptographic Signature in matrix-synapse
- CVE-2024-52815 Synapse allows a a malformed invite to break the invitee's `/sync`
- CVE-2024-52805 Synapse allows unsupported content types to lead to memory exhaustion
- CVE-2024-53863 Synapse can be forced to thumbnail unexpected file formats, invoking external, potentially untrustworthy decoders
- CVE-2024-37302 Synapse denial of service through media disk space consumption
Sources
Also known as GHSA-98px-6486-j7qc, PYSEC-2023-85, UBUNTU-CVE-2023-32683.