CVE-2022-24825 is a Server-Side Request Forgery (SSRF) vulnerability identified in the Stripe Smokescreen HTTP proxy, specifically in versions prior to 0.0.3. Smokescreen is designed to act as a protective proxy that prevents SSRF attacks by filtering and controlling outbound HTTP requests from applications, effectively blocking access to unauthorized or potentially dangerous URLs. It achieves this by implementing a deny list to restrict access to certain external or internal URLs. The vulnerability arises from inadequate normalization and validation of user-supplied URLs, allowing attackers to bypass the deny list by appending a trailing dot to URLs or by manipulating the letter casing of the URLs. This bypass enables an attacker to trick Smokescreen into forwarding requests to otherwise blocked destinations, potentially allowing unauthorized access to internal infrastructure or sensitive services behind the proxy. Exploiting this vulnerability does not require authentication or user interaction, as it targets the proxy's URL filtering mechanism directly. Although no known exploits have been reported in the wild, the flaw presents a significant risk because SSRF can be leveraged to perform internal network reconnaissance, access internal-only services, or exploit trust relationships within the network. The recommended remediation is to upgrade Smokescreen to version 0.0.3 or later, where proper normalization and case-insensitive checks have been implemented to close this bypass vector.

For European organizations, the impact of this SSRF vulnerability can be substantial, especially for those relying on Smokescreen to secure internal services and prevent unauthorized outbound requests. Successful exploitation could lead to unauthorized access to internal systems, potentially exposing sensitive data or enabling lateral movement within corporate networks. This is particularly critical for sectors with stringent data protection requirements such as finance, healthcare, and government agencies. The vulnerability could also facilitate reconnaissance activities that precede more severe attacks, including data exfiltration or disruption of services. Given the reliance on internal APIs and microservices in modern European enterprises, an SSRF vulnerability undermines the integrity and confidentiality of internal communications. While availability impact is generally lower for SSRF, attackers could potentially use it to trigger denial-of-service conditions on internal services by flooding them with requests. The medium severity rating reflects the balance between the ease of exploitation (no authentication needed) and the requirement that the vulnerable proxy is in use and exposed to attacker-controlled input.

To mitigate this vulnerability effectively, European organizations should: 1) Immediately upgrade all instances of Stripe Smokescreen to version 0.0.3 or later to ensure proper URL normalization and deny list enforcement. 2) Implement strict input validation and sanitization on all user-supplied URLs before they reach the proxy to reduce the risk of malformed or obfuscated URLs bypassing filters. 3) Employ network segmentation and strict egress filtering to limit the proxy’s ability to reach sensitive internal services, reducing the impact of any SSRF exploitation. 4) Monitor proxy logs for unusual URL patterns, such as URLs with trailing dots or mixed case variations, which may indicate attempts to exploit this vulnerability. 5) Conduct regular security assessments and penetration tests focusing on SSRF vectors to identify and remediate similar weaknesses. 6) Where possible, implement allow lists instead of deny lists for outbound requests to minimize the attack surface. 7) Educate developers and security teams about SSRF risks and secure proxy configuration best practices.