CVE-2023-32683 : Security Advisory and Response

A vulnerability in Synapse allows threat actors to bypass URL deny lists via oEmbed and image URLs when generating previews, potentially leading to server-side request forgery or network policy bypass.

Understanding CVE-2023-32683

This CVE discloses a security flaw in Synapse that affects systems running versions prior to 1.85.0. The vulnerability enables threat actors to bypass specific URL deny list settings, potentially compromising server security.

What is CVE-2023-32683?

CVE-2023-32683 exposes a flaw in Synapse's handling of oEmbed and image URLs, allowing threat actors to evade deny list restrictions and potentially carry out server-side request forgery attacks or bypass network policies.

The Impact of CVE-2023-32683

The impact of this vulnerability is limited to IP addresses allowed by specific server settings related to URL previews. Systems with URL preview disabled or properly configured deny list settings are not affected. However, exploitation could lead to unauthorized access or manipulation of server resources.

Technical Details of CVE-2023-32683

The vulnerability description, affected systems, and exploitation mechanism are detailed below:

Vulnerability Description

Synapse, a Python-based Matrix protocol homeserver, fails to properly enforce deny list restrictions for oEmbed and image URLs, potentially allowing threat actors to perform unauthorized actions.

Affected Systems and Versions

Organizations running Synapse versions earlier than 1.85.0 are impacted by this vulnerability. Updating to version 1.85.0 or newer is crucial to mitigate the risk of exploitation.

Exploitation Mechanism

Threat actors can exploit this vulnerability by leveraging discovered oEmbed or image URLs to circumvent deny list settings, enabling server-side request forgery or network policy evasion.

Mitigation and Prevention

To secure your systems against CVE-2023-32683, consider the following mitigation strategies:

Immediate Steps to Take

Upgrade Synapse to version 1.85.0 or above to address the vulnerability.

Long-Term Security Practices

Regularly update and patch software to prevent known vulnerabilities.
Implement proper deny list configurations and security settings to restrict malicious activities.

Patching and Updates

Stay informed about security advisories and promptly apply patches released by the vendor to enhance system security.