URL deny list bypass via oEmbed and image URLs when generating previews in Synapse
Key facts
- Attack vector
- Network
- Privileges required
- Low
- User interaction
- None
- Attack complexity
- Low
- Impact type
- Security bypass
- Confidentiality · integrity · availability
- Low · Low · None
- Fix status
- Fixed
Attack profile from CVSS 3.1 · NVD. Fix status from CNA and GitHub. Impact type from CWE-863.
Summary
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.
Why it matters now
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- None
- Automatable
- No
- Technical impact
- Partial
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| matrix-org | synapse | before 1.85.0 | 1.85.0 | Patch available | CNA |
| — | matrix-synapse (PyPI) | before 1.85.0 | 1.85.0 | Patch available | GHSA-98px-6486-j7qc |
- synapse Vendormatrix-org Affected before 1.85.0 Fixed in 1.85.0 Patch available CNA
- matrix-synapse (PyPI) Vendor— Affected before 1.85.0 Fixed in 1.85.0 Patch available GHSA-98px-6486-j7qc
CPE configurations NVD · 1
| CPE | Versions | Role | Vendor |
|---|---|---|---|
| cpe:2.3:a:matrix:synapse:*:*:*:*:*:*:*:* | before 1.85.0 | Vulnerable | matrix-org |
- cpe:2.3:a:matrix:synapse:*:*:*:*:*:*:*:* Versions before 1.85.0 Vulnerable ·matrix-org
Remediation
- Fix · CNA synapse (matrix-org) Fixed in 1.85.0
- Fix · GHSA-98px-6486-j7qc matrix-synapse (PyPI) Fixed in 1.85.0 Advisory →
Vendor assessments
Timeline
- 2026-10-02 Threatist record created from CVE-2023-32683
- 2026-10-03 Alias added: GHSA-98px-6486-j7qc
References
Patch 2
Other 5
- https://lists.fedoraproject.org/archives/list/[email protected]/message/X6DH5A5YEB5LRIPP32OUW25FCGZFCZU2/
- 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/[email protected]/message/X6DH5A5YEB5LRIPP32OUW25FCGZFCZU2
More matrix-org Synapse vulnerabilities
- TI-2023-15617 Synapse Outgoing federation to specific hosts can be disabled by sending malicious invites CVSS 3.1MEDIUM 5.0
- TI-2024-35327 Synapse allows a a malformed invite to break the invitee's `/sync` CVSS 4.0HIGH 8.7
- TI-2019-13571 Matrix Synapse before 1.5.0 mishandles signature checking on some federation APIs. CVSS 3.1CRITICAL 9.8
- TI-2024-36056 Synapse can be forced to thumbnail unexpected file formats, invoking external, potentially untrustworthy decoders CVSS 4.0HIGH 8.2
- TI-2024-35318 Synapse allows unsupported content types to lead to memory exhaustion CVSS 4.0HIGH 8.2
- TI-2018-11846 Matrix Synapse before 0.33.3.1 allows remote attackers to spoof events and possibly have… CVSS 3.0HIGH 8.8
Sources
- CVE-2023-32683 · CVE Program
- CVE-2023-32683 · NVD
- FIRST EPSS
- GHSA-98px-6486-j7qc · GitHub Advisory Database · CC BY 4.0
- CVE-2023-32683 · Red Hat security data · CC BY 4.0
This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences