CVE-2023-32683

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.

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.

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.

These are all security issues fixed in the matrix-synapse-1.85.2-1.1 package on the GA media of openSUSE Tumbleweed.

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.

It was discovered that Synapse network policies could be bypassed via specially crafted URLs. An attacker could possibly use this issue to bypass authentication mechanisms. (CVE-2023-32683)

It was discovered that Synapse exposed cached device information. An attacker could possibly use this issue to gain access to sensitive information. (CVE-2023-43796)

It was discovered that Synapse could be tricked into rejecting state changes in rooms. An attacker could possibly use this issue to cause Synapse to stop functioning properly, resulting in a denial of service. This issue was only fixed in Ubuntu 20.04 LTS and Ubuntu 22.04 LTS. (CVE-2022-39374)

It was discovered that Synapse stored user credentials in a server's database temporarily. An attacker could possibly use this issue to gain access to sensitive information. This issue was only fixed in Ubuntu 22.04 LTS. (CVE-2023-41335)

It was discovered that Synapse could incorrectly respond to server authorization events. An attacker could possibly use this issue to bypass authentication mechanisms. This issue was only fixed in Ubuntu 22.04 LTS. (CVE-2022-39335)

It was discovered that Synapse could be manipulated to mark messages as read when they had not been viewed. An attacker could possibly use this issue to perform repudiation-based attacks. This issue was only fixed in Ubuntu 22.04 LTS. (CVE-2023-42453)

It was discovered that Synapse had several memory-related issues. An attacker could possibly use this issue to cause Synapse to crash, resulting in a denial of service. This issue was only fixed in Ubuntu 22.04 LTS. (CVE-2024-31208)

It was discovered that Synapse could run external tools due to a unchecked thumbnail rendering routine. An attacker could possibly use this issue to cause Synapse to crash, resulting in a denial of service, or execute arbitrary code. This issue was only fixed in Ubuntu 22.04 LTS. (CVE-2024-53863)