CVE-2026-61554 in emp3r0r
Summary
by MITRE • 09/15/2026
emp3r0r is a C2 designed by Linux users for Linux environments. Prior to version 4.2.5, the `http_poll` C2 transport accepts attacker-controlled HTTP polling sessions before CBOR `MsgAuth` authentication is completed. A remote unauthenticated attacker can create arbitrary polling sessions and send request bodies that are forwarded into the C2 dispatch path. This can consume server resources and trigger pre-auth C2 processing. Version 4.2.5 patches the issue.
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Analysis
by VulDB Data Team • 09/15/2026
The vulnerability identified in emp3r0r versions prior to 4.2.5 represents a critical authentication bypass within its command-and-control communication architecture. Emp3r0r is designed as a Linux-native C2 framework, and like many such tools, it relies on specific transport protocols to facilitate interaction between the operator's controller and compromised hosts. The core of this flaw lies in the http_poll transport mechanism, which handles HTTP-based polling sessions from clients seeking instructions or sending data back to the server. In vulnerable versions, the system fails to enforce authentication checks before accepting incoming connections for these polling sessions. This architectural oversight allows a remote unauthenticated attacker to establish communication channels with the C2 infrastructure without providing valid credentials, effectively bypassing the intended access controls that are supposed to restrict interaction to authorized operators only.
From a technical perspective, the issue stems from the order of operations in the request handling pipeline. When an HTTP polling session is initiated, the server accepts the connection and begins processing the incoming data before verifying the CBOR MsgAuth authentication payload. This sequence error means that any client can inject arbitrary request bodies into the C2 dispatch path immediately upon connection establishment. The dispatcher then processes these requests as if they were authenticated commands or valid operational inputs. This behavior not only violates the principle of least privilege but also exposes internal processing logic to external actors who should have no access to the system's command structure.
The operational impact of this vulnerability is significant, primarily due to resource exhaustion and potential unauthorized execution. Since an unauthenticated attacker can create arbitrary polling sessions, they can flood the server with connections, leading to a denial-of-service condition by consuming CPU cycles, memory, and network bandwidth associated with maintaining these fake sessions. Furthermore, because request bodies are forwarded into the dispatch path before authentication, there is a risk that maliciously crafted payloads could trigger unintended side effects within the C2 logic. While emp3r0r may not execute arbitrary code directly from HTTP polls in all configurations, the ability to interact with the internal dispatcher opens avenues for further exploitation, such as probing system capabilities or attempting to escalate privileges through subsequent authenticated interactions if other flaws exist.
This vulnerability aligns closely with CWE-287 Improper Authentication and CWE-362 Concurrent Execution using Shared Resource with Improper Synchronization (if race conditions are involved in session handling), though it is most directly categorized under CWE-306 Missing Authentication for Critical Function. In the context of the MITRE ATT&CK framework, this flaw facilitates Initial Access by allowing an adversary to establish a foothold or communication channel without detection via credential theft. It also supports Discovery and Command and Control tactics, as the attacker can interact with the C2 server's internal mechanisms to understand its capabilities and potentially issue commands if additional vulnerabilities are present in the unauthenticated dispatch path.
To mitigate this risk, organizations using emp3r0r must upgrade immediately to version 4.2.5 or later, where the authentication check is correctly positioned before accepting polling sessions. For environments that cannot patch instantly due to operational constraints, network-level controls should be implemented to restrict access to the C2 server's HTTP endpoints exclusively to known operator IP addresses using firewall rules or reverse proxy configurations with strict ACLs. Additionally, implementing rate limiting on incoming connections can help mitigate denial-of-service attempts resulting from session flooding. Regular security audits of custom-built or open-source C2 frameworks are essential to ensure that authentication and authorization checks are applied consistently across all communication channels before any processing occurs.