CVE-2026-35540
Description
A flaw was found in Roundcube Webmail. Insufficient sanitization of Cascading Style Sheets (CSS) in HTML e-mail messages may allow a remote attacker to perform Server-Side Request Forgery (SSRF) or disclose sensitive information. This can occur if malicious stylesheet links within an e-mail point to internal network hosts, potentially allowing an attacker to make requests from the server or gain unauthorized access to data.
Statement
Red Hat Product Security has determined that this vulnerability does not affect any currently supported Red Hat product. This assessment may evolve based on further analysis and discovery. For more information about this vulnerability and the products it affects, please see the linked references.
Understanding the Weakness (CWE)
Confidentiality
Technical Impact: Read Application Data
Integrity
Technical Impact: Execute Unauthorized Code or Commands
Access Control
Technical Impact: Bypass Protection Mechanism
By providing URLs to unexpected hosts or ports, attackers can make it appear that the server is sending the request, possibly bypassing access controls such as firewalls that prevent the attackers from accessing the URLs directly. The server can be used as a proxy to conduct port scanning of hosts in internal networks, use other URLs such as that can access documents on the system (using file://), or use other protocols such as gopher:// or tftp://, which may provide greater control over the contents of requests.
Frequently Asked Questions
Not sure what something means? Check out our Security Glossary.
Want to get errata notifications? Sign up here.
