CVE-2025-8396 is a medium-severity vulnerability affecting the Temporal OSS Server, specifically versions prior to 1.26.3, 1.27.3, and 1.28.1. The root cause is insufficiently specific bounds checking on the authorization header, which can lead to excessive memory allocation. This vulnerability is categorized under CWE-770, which involves allocation of resources without limits or throttling. An attacker can exploit this flaw remotely without any authentication or user interaction by sending specially crafted authorization headers to the Temporal OSS Server. The excessive memory allocation can cause a denial of service (DoS) condition, potentially crashing the server or severely degrading its performance. Temporal Cloud services are not impacted by this vulnerability, limiting the scope to self-hosted OSS Server deployments. The CVSS 4.0 base score is 6.9, reflecting a medium severity with network attack vector, low attack complexity, no privileges or user interaction required, and a low impact on availability. No known exploits are currently reported in the wild. The vulnerability affects all platforms running the vulnerable versions, making it a cross-platform issue. The lack of throttling or limits on resource allocation in processing authorization headers is the key technical weakness, allowing attackers to consume excessive server memory and cause service disruption.

For European organizations using Temporal OSS Server in their infrastructure, this vulnerability poses a risk of denial of service attacks that can disrupt critical workflow orchestration and automation services. Temporal OSS Server is often used in microservices orchestration, business process automation, and distributed system coordination. A successful DoS attack could lead to downtime, loss of productivity, and potential cascading failures in dependent systems. Since the attack requires no authentication or user interaction, it can be launched by any remote attacker with network access to the server, increasing the risk profile. Organizations in sectors such as finance, manufacturing, telecommunications, and public services that rely on Temporal OSS Server for orchestrating backend processes may experience operational disruptions. Although the vulnerability does not directly compromise confidentiality or integrity, the availability impact can have significant business consequences. The fact that Temporal Cloud services are unaffected means organizations using managed cloud offerings are not at risk, but those running on-premises or private cloud OSS Server instances must prioritize patching. The medium severity rating suggests the threat is notable but not critical, yet the ease of exploitation and potential service impact warrant timely remediation.

European organizations should immediately identify all Temporal OSS Server instances running vulnerable versions (prior to 1.26.3, 1.27.3, and 1.28.1). The primary mitigation is to upgrade these servers to the fixed versions 1.26.3, 1.27.3, 1.28.1, or later. If immediate patching is not feasible, organizations can implement network-level protections such as rate limiting and deep packet inspection on authorization headers to detect and block anomalous or excessively large authorization header values. Deploying Web Application Firewalls (WAFs) or Intrusion Prevention Systems (IPS) with custom rules to throttle or drop suspicious requests targeting Temporal OSS Server endpoints can reduce exposure. Monitoring server memory usage and setting resource limits or container memory caps can help mitigate impact. Additionally, restricting network access to Temporal OSS Server to trusted internal networks or VPNs reduces attack surface. Organizations should also review logs for unusual authorization header patterns indicative of exploitation attempts. Finally, integrating vulnerability management processes to track Temporal OSS Server versions and automate patch deployment will prevent recurrence.