CVE-2026-23735 is a concurrency-related vulnerability classified under CWE-362 (Race Condition) affecting graphql-hive's graphql-modules library, a popular toolset for building modular GraphQL servers. The vulnerability arises when two or more parallel requests invoke the same service, and the context injection mechanism via the @ExecutionContext() decorator improperly synchronizes shared resources. Specifically, the context object, which often carries authentication tokens and user-specific data, can become intermingled between concurrent requests. This leads to a scenario where one request might inadvertently access or manipulate another request's context, potentially exposing sensitive information or allowing unauthorized actions. The flaw exists in graphql-modules versions from 2.2.1 up to but not including 2.4.1, and from 3.0.0 up to but not including 3.1.1. The vulnerability is remotely exploitable without any authentication or user interaction, increasing its risk profile. The CVSS 4.0 vector (AV:N/AC:L/AT:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N) highlights network attack vector, low complexity, no privileges or user interaction required, and high impact on confidentiality. The vulnerability was publicly disclosed on January 16, 2026, and patched in versions 2.4.1 and 3.1.1. Although no active exploits have been reported, the nature of the flaw makes it a significant risk for any GraphQL API relying on these versions, especially where authentication tokens are passed via ExecutionContext. Attackers could exploit this to gain unauthorized access to user data or perform actions on behalf of other users.

For European organizations, this vulnerability poses a serious risk to the confidentiality and integrity of user data handled by GraphQL APIs using the affected graphql-modules versions. Since the flaw allows context leakage between concurrent requests, sensitive authentication tokens and user-specific information could be exposed or misused, leading to unauthorized data access or privilege escalation. This could result in data breaches, regulatory non-compliance (e.g., GDPR violations), reputational damage, and potential financial penalties. Organizations in sectors with high data sensitivity such as finance, healthcare, and government are particularly at risk. The vulnerability's ease of exploitation without authentication or user interaction increases the likelihood of automated attacks or exploitation by malicious insiders. Additionally, the shared resource race condition could cause inconsistent application behavior, impacting service reliability and availability indirectly. Given the widespread adoption of GraphQL in modern web services, the scope of affected systems across Europe could be substantial if unpatched.

European organizations should immediately identify any deployments of graphql-hive graphql-modules within the affected version ranges (>=2.2.1 and <2.4.1, >=3.0.0 and <3.1.1). The primary mitigation is to upgrade to patched versions 2.4.1 or 3.1.1 as soon as possible. If immediate upgrade is not feasible, organizations should implement strict request serialization or limit concurrency on services using @ExecutionContext() to reduce the risk of context mixing. Additionally, review and enhance logging and monitoring around GraphQL API requests to detect anomalous access patterns or context leakage. Employ runtime application self-protection (RASP) or web application firewalls (WAF) with custom rules to monitor and potentially block suspicious concurrent request patterns. Conduct thorough code reviews to ensure proper synchronization when handling shared resources in custom modules. Finally, enforce strict token scopes and short token lifetimes to minimize the impact of any leaked authentication context.