CVE-2022-27516 is a vulnerability identified in Citrix Gateway and Citrix ADC products, categorized under CWE-693, which relates to protection mechanism failures. Specifically, this vulnerability allows an attacker to bypass the user login brute force protection functionality. Normally, brute force protection mechanisms are designed to detect and block repeated login attempts to prevent unauthorized access through credential guessing. However, due to this flaw, the protection mechanism can be circumvented, enabling an attacker to perform unlimited login attempts without triggering lockouts or alerts. The vulnerability has a CVSS v3.1 base score of 5.3, indicating a medium severity level. The vector metrics are AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N, meaning the attack can be launched remotely over the network without any privileges or user interaction, and it impacts the integrity of the system by potentially allowing unauthorized access through compromised credentials, but does not affect confidentiality or availability. No known exploits in the wild have been reported as of the publication date (November 8, 2022), and no patches are currently linked, suggesting that mitigation may require vendor updates or configuration changes once available. Citrix Gateway and ADC are widely used for secure remote access and application delivery, making this vulnerability significant in environments relying on these products for authentication and access control.

For European organizations, the bypass of brute force protection in Citrix Gateway and ADC can lead to increased risk of unauthorized access through credential stuffing or brute force attacks. Since these products are commonly deployed in enterprise environments to provide secure remote access to internal networks and applications, successful exploitation could allow attackers to gain footholds within corporate networks, potentially leading to lateral movement and data integrity compromise. Although confidentiality and availability are not directly impacted by this vulnerability, the integrity impact (unauthorized access) can result in further exploitation, including data manipulation or deployment of additional malware. Critical sectors such as finance, healthcare, government, and telecommunications in Europe that rely on Citrix infrastructure for remote access are particularly at risk. The medium CVSS score reflects that while exploitation does not require privileges or user interaction, the impact is limited to integrity and does not directly cause data leakage or service disruption. However, the ease of exploitation and the widespread use of Citrix products in Europe elevate the risk profile for organizations that have not implemented compensating controls or applied patches once available.

1. Immediate mitigation should include monitoring and alerting on anomalous login attempts and patterns indicative of brute force attacks against Citrix Gateway and ADC instances. 2. Implement network-level protections such as rate limiting, IP blacklisting, or geo-blocking to reduce exposure to automated login attempts. 3. Enforce strong multi-factor authentication (MFA) on all Citrix Gateway and ADC access points to mitigate the risk of credential compromise even if brute force attempts succeed. 4. Regularly review and update access control lists and ensure that only necessary users and IP ranges have access to Citrix services. 5. Apply vendor patches or updates as soon as they become available to address the vulnerability directly. 6. Consider deploying Web Application Firewalls (WAF) or Intrusion Prevention Systems (IPS) with signatures or heuristics tuned to detect brute force bypass attempts targeting Citrix products. 7. Conduct periodic penetration testing and vulnerability assessments focused on authentication mechanisms in Citrix environments to identify and remediate weaknesses proactively.