CVE-2025-53537 is a high-severity vulnerability identified in libhtp, a security-aware HTTP protocol parser used by the Open Information Security Foundation (OISF) in their Suricata intrusion detection and prevention system. The vulnerability is classified under CWE-401, which pertains to missing release of memory after its effective lifetime, commonly known as a memory leak. Specifically, in libhtp versions 0.5.50 and below, certain traffic patterns induce a memory leak that can progressively consume available memory resources within the process. This memory exhaustion can lead to a denial of service condition by starving the Suricata process of memory, thereby causing loss of visibility into network traffic and potentially allowing malicious activity to go undetected. The vulnerability does not impact confidentiality or integrity directly but severely impacts availability and operational reliability of network security monitoring. The issue arises from the improper handling of memory allocations related to the LZMA compression feature within the HTTP protocol parser. The vendor recommends a temporary workaround by disabling the LZMA feature via the Suricata configuration parameter `suricata.yaml app-layer.protocols.http.libhtp.default-config.lzma-enabled` set to false. The vulnerability is fixed in libhtp version 0.5.51. The CVSS v3.1 base score is 7.5, reflecting a network attack vector with low attack complexity, no privileges or user interaction required, and a high impact on availability. No known exploits are reported in the wild as of the publication date, but the potential for denial of service in critical network monitoring infrastructure makes this a significant concern.

For European organizations, the impact of CVE-2025-53537 can be substantial, particularly for those relying on Suricata or other security tools that embed libhtp for HTTP traffic analysis. The memory leak can degrade or disable network intrusion detection capabilities, leading to blind spots in monitoring and increased risk of undetected cyberattacks. This is especially critical for sectors with stringent cybersecurity requirements such as finance, telecommunications, critical infrastructure, and government agencies. Loss of visibility can delay incident detection and response, increasing the likelihood of successful exploitation by threat actors. Additionally, organizations with high network traffic volumes may experience accelerated memory exhaustion, exacerbating the denial of service impact. The vulnerability does not compromise data confidentiality or integrity directly but undermines the security posture by impairing detection capabilities, which can indirectly facilitate data breaches or service disruptions.

To mitigate this vulnerability, European organizations should promptly upgrade libhtp to version 0.5.51 or later where the memory leak is fixed. Until the upgrade can be applied, the recommended workaround is to disable the LZMA compression feature in the Suricata configuration by setting `suricata.yaml app-layer.protocols.http.libhtp.default-config.lzma-enabled` to false. Organizations should also monitor memory usage of Suricata processes closely to detect abnormal consumption patterns indicative of exploitation. Implementing resource limits or containerization can help contain the impact of memory leaks. Regularly updating Suricata and libhtp components as part of patch management is critical. Network security teams should validate that their monitoring tools are not impacted and consider fallback detection mechanisms to maintain visibility. Finally, reviewing network traffic for unusual patterns that may trigger the memory leak can help preempt denial of service conditions.