CVE-2026-114426 in Secure Email Gateway
Summary
by MITRE • 11/04/2026
SEPPmail Secure Email Gateway before 15.1.1 processes and writes v1 file-interface upload data before authenticating the caller and without an absolute request-size limit. An unauthenticated remote attacker can occupy workers and consume temporary storage with concurrent or slow requests, causing service unavailability.
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Analysis
by VulDB Data Team • 11/04/2026
The vulnerability identified in SEPPmail Secure Email Gateway versions prior to 15.1.1 represents a critical failure in the application's authentication and input validation mechanisms within its file-interface upload functionality. Specifically, the system is designed to process and write data associated with v1 file uploads before verifying the identity of the caller or enforcing strict limits on request size. This architectural flaw allows an unauthenticated remote attacker to interact directly with the backend processing workers without first passing through standard authentication gates. By exploiting this sequence error, where resource allocation precedes access control verification, attackers can bypass security controls that are intended to restrict such operations to authorized users only.
From a technical perspective, the core issue lies in the lack of an absolute request-size limit combined with premature data processing. When a client initiates an upload, the server immediately begins allocating memory and disk space for the incoming payload before checking credentials or validating the integrity of the connection parameters. This behavior creates two distinct vectors for exploitation: resource exhaustion through volume and denial-of-service via concurrency control failures. An attacker can submit multiple concurrent requests to saturate the available worker threads, effectively blocking legitimate traffic from being processed. Alternatively, by sending slow but continuous streams of data, an attacker can keep connections open indefinitely, tying up server resources over time without ever completing a valid transaction.
The operational impact of this vulnerability is severe, primarily manifesting as a denial-of-service condition that compromises the availability of the email gateway service. Since SEPPmail serves as a critical infrastructure component for organizational communication, any disruption affects business continuity and potentially exposes sensitive data if fallback mechanisms are triggered or if attackers use the distraction to attempt other attacks. The consumption of temporary storage can also lead to disk space exhaustion on the underlying host system, which may cause broader system instability beyond just the application layer. This aligns with CWE-787: Out-of-bounds Write and CWE-400: Uncontrolled Resource Consumption, as the system fails to properly limit resource usage based on untrusted input.
In terms of threat modeling, this vulnerability is consistent with ATT&CK technique T1496: Resource Hijacking, where adversaries consume computational resources to degrade service performance or cause outages. It also reflects CWE-287: Improper Authentication, as the system processes sensitive operations without verifying user identity first. The ability to occupy workers and fill temporary storage demonstrates a classic server-side request forgery pattern combined with resource exhaustion tactics often seen in high-volume DDoS attacks but executed here through application-layer logic flaws rather than network-level flooding alone.
To mitigate this vulnerability, organizations running SEPPmail Secure Email Gateway must immediately upgrade to version 15.1.1 or later, where these authentication and size-limiting checks have been corrected. Until the patch is applied, administrators should consider implementing network-level controls such as rate limiting at the firewall or load balancer level to restrict the number of concurrent connections from single IP addresses. Additionally, configuring web application firewalls to detect and block unusually large POST requests can help reduce the impact of resource exhaustion attempts. It is also advisable to review logging configurations to ensure that failed authentication attempts on upload endpoints are monitored closely for signs of automated scanning or exploitation activity.