CVE-2026-97666 in Nexus Repository
Summary
by MITRE • 10/15/2026
Sonatype Nexus Repository 3 allows an unauthenticated remote attacker to supply attacker-controlled input to a Java class loading call through an ExtDirect endpoint. This allows the attacker to learn whether specific classes are present in the application. The issue does not by itself allow code execution.
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Analysis
by VulDB Data Team • 10/15/2026
The vulnerability identified in Sonatype Nexus Repository 3 stems from improper validation of user-supplied input within the ExtDirect API endpoints, which serve as a primary interface for client-server communication in this repository management platform. An unauthenticated remote attacker can exploit this flaw by crafting specific HTTP requests that target internal Java class loading mechanisms exposed through these endpoints. The core technical issue lies in the application's failure to adequately sanitize or restrict input parameters before they are processed by reflection-based class resolution routines. When a request is received, the backend logic attempts to load and inspect classes based on the provided identifiers without sufficient verification of whether those inputs correspond to legitimate, expected types within the application context. This lack of strict allow-listing or rigorous type checking creates an information disclosure vector that allows external actors to probe the internal structure of the Java Virtual Machine environment hosting the Nexus instance.
The operational impact of this vulnerability is primarily centered on reconnaissance and intelligence gathering rather than immediate system compromise. By sending carefully constructed requests, an attacker can determine whether specific classes are present in the classpath by observing differences in server responses or error messages. This capability enables a detailed mapping of the application's dependencies, including third-party libraries, framework versions, and internal modules that may not be visible through standard interface interactions. While this vulnerability does not directly facilitate arbitrary code execution due to restrictions on how classes are instantiated and invoked, it significantly lowers the barrier for subsequent attacks. Knowledge of specific class availability can aid attackers in identifying known vulnerabilities within those particular library versions or in crafting more sophisticated exploits that rely on the presence of certain components, such as deserialization gadgets or insecure configuration handlers.
From a classification perspective, this issue aligns with CWE-209, which describes the generation of error messages containing sensitive information about an environment, and CWE-754, relating to improper check for unusual or exceptional conditions during class loading. The exploitation technique falls under MITRE ATT&CK tactic TA0006, Discovery, specifically sub-technique T1583.002, Acquire Infrastructure: Domains, although in this context it is more accurately mapped to information gathering about the target environment's software composition. This phase of an attack chain is critical for adversaries seeking to understand the technical landscape before attempting privilege escalation or data exfiltration. The ability to fingerprint internal classes effectively reveals the underlying technology stack and potential weak points that are not exposed through normal user workflows, thereby expanding the effective attack surface beyond what is immediately apparent from public documentation or default configurations.
Mitigation strategies for this vulnerability require a multi-layered approach focusing on input validation and access control. First, administrators should ensure that all ExtDirect endpoints enforce strict authentication requirements, preventing unauthenticated users from accessing any API functionality regardless of intent. Second, the application logic must implement rigorous allow-listing for class names or identifiers passed to reflection-based loading methods, ensuring that only explicitly approved classes can be resolved. Input sanitization routines should reject any input containing characters or patterns indicative of path traversal or invalid type specifications. Additionally, deploying a Web Application Firewall with rules tuned to detect abnormal API request patterns related to class loading and reflection abuse can provide an additional layer of defense. Regular patching is essential; users must upgrade Sonatype Nexus Repository 3 to the latest version where these input validation checks have been hardened by the vendor. Continuous monitoring for unusual HTTP requests targeting internal APIs should also be implemented to detect potential probing activities in real-time, allowing security teams to respond before further reconnaissance or exploitation attempts occur.