CVE-2025-53538 is a high-severity vulnerability affecting Suricata, an open-source network intrusion detection and prevention system (IDS/IPS) and network security monitoring (NSM) engine developed by the Open Information Security Foundation (OISF). The vulnerability arises from improper handling of data on HTTP/2 stream 0 in Suricata versions 7.0.10 and below, as well as versions 8.0.0-beta1 through 8.0.0-rc1. Specifically, Suricata fails to impose limits or throttling on resource allocation when processing HTTP/2 stream 0 frames, leading to uncontrolled memory consumption. This flaw is categorized under CWE-770 (Allocation of Resources Without Limits or Throttling) and CWE-400 (Uncontrolled Resource Consumption). The exploitation of this vulnerability does not impact confidentiality or integrity but results in a denial of service condition by exhausting memory resources, causing Suricata to lose visibility into network traffic. This can critically impair network security monitoring and intrusion detection capabilities. The vulnerability can be mitigated temporarily by disabling the HTTP/2 parser or by deploying a custom Suricata signature that drops HTTP/2 frames on stream 0, effectively preventing the problematic frames from being processed. The issue is resolved in Suricata versions 7.0.11 and 8.0.0 and later. The CVSS v3.1 base score is 7.5, reflecting a high severity due to network attack vector, no required privileges or user interaction, and a significant impact on availability.

For European organizations, the impact of this vulnerability is significant, especially for those relying on Suricata for network security monitoring and intrusion detection. The uncontrolled memory usage can lead to denial of service, causing Suricata to crash or become unresponsive, which results in loss of visibility into network traffic and potential blind spots for detecting malicious activity. This can delay incident detection and response, increasing the risk of successful cyberattacks or data breaches. Critical infrastructure sectors such as finance, energy, telecommunications, and government agencies that deploy Suricata as part of their security stack are particularly at risk. The disruption of IDS/IPS capabilities can also affect compliance with European data protection regulations like GDPR, which require adequate security measures to protect personal data. Additionally, the vulnerability could be exploited remotely without authentication, increasing the risk of widespread attacks if threat actors target exposed Suricata deployments.

European organizations should prioritize upgrading Suricata to version 7.0.11 or 8.0.0 (or later) as soon as possible to fully remediate the vulnerability. Until upgrades can be applied, organizations should disable the HTTP/2 parser in Suricata configurations to prevent processing of vulnerable HTTP/2 frames. Deploying the recommended Suricata signature that drops HTTP/2 frames on stream 0 can serve as an effective temporary workaround to limit memory exhaustion. Network administrators should monitor Suricata instances for unusual memory usage or crashes that could indicate exploitation attempts. Additionally, organizations should implement network segmentation and limit exposure of Suricata sensors to untrusted networks to reduce attack surface. Regularly reviewing and updating IDS/IPS signatures and configurations to detect anomalous HTTP/2 traffic patterns can also help mitigate risks. Finally, maintaining robust incident response plans to quickly address potential denial of service events will minimize operational impact.