CVE-2025-37756 is a vulnerability identified in the Linux kernel's implementation of TLS (Transport Layer Security) socket handling, specifically within the network subsystem. The issue arises from the kernel's inability to properly handle the disconnection of TLS sockets. The vulnerability was discovered by syzbot, an automated kernel fuzzer, which found that disconnecting a TLS socket leads to unexpected corner cases and kernel warnings, including a critical warning in the tls_strp_msg_load function. The root cause is that the Linux kernel's TLS offload mechanism does not correctly manage the disconnect operation, particularly when offload is enabled and packets need to be acknowledged before disconnecting. Since disconnect is not commonly used in TLS sockets, the kernel maintainers decided to explicitly disallow disconnect operations on TLS sockets to avoid these complex edge cases. The vulnerability manifests as a kernel warning and potentially unstable behavior in the TLS socket receive path, which could lead to kernel crashes or denial of service. The affected versions are identified by a specific commit hash, indicating that the vulnerability exists in certain Linux kernel builds prior to the patch. No known exploits are reported in the wild as of the publication date, and no CVSS score has been assigned yet. The vulnerability primarily impacts the confidentiality, integrity, and availability of systems using Linux kernel TLS offload features, especially in environments where TLS socket disconnect operations might be invoked.

For European organizations, this vulnerability poses a risk primarily to servers and infrastructure running Linux kernels with TLS offload enabled. Such systems are common in data centers, cloud providers, and enterprise environments that rely on Linux for secure communications. The vulnerability could lead to kernel panics or denial of service conditions, disrupting critical services and potentially exposing sensitive communications to interruption. Although no direct remote code execution or privilege escalation is indicated, the instability caused by improper TLS socket disconnect handling could degrade service availability. Organizations in sectors such as finance, healthcare, telecommunications, and government, which heavily depend on secure and reliable Linux-based infrastructure, may experience operational disruptions. Additionally, the lack of a known exploit does not preclude future weaponization, especially as attackers often target kernel vulnerabilities to cause widespread outages or to facilitate further attacks. The impact is heightened in environments using advanced TLS offload features for performance optimization, which are more prevalent in high-throughput network environments.

European organizations should take the following specific actions to mitigate this vulnerability: 1) Identify and inventory Linux systems running kernel versions affected by the commit hash referenced in the vulnerability report. 2) Apply the latest Linux kernel patches that explicitly disallow TLS socket disconnect operations, ensuring that the kernel source or distribution-provided updates include this fix. 3) Disable TLS offload features temporarily if patching is not immediately feasible, as this reduces exposure to the disconnect-related corner cases. 4) Audit applications and services to detect any use of TLS socket disconnect calls and modify them to avoid invoking disconnect on TLS sockets. 5) Implement kernel crash monitoring and alerting to quickly detect and respond to any instability related to TLS socket operations. 6) Engage with Linux distribution vendors for timely security updates and verify that security advisories are followed. 7) Conduct penetration testing and fuzzing on critical systems to identify any residual issues related to TLS socket handling. These measures go beyond generic patching by focusing on configuration adjustments and operational monitoring tailored to the TLS offload context.