CVE-2026-2743 in Web Interface
Summary
by MITRE • 03/05/2026
Arbitrary File Write via Path Traversal upload to Remote Code Execution in SeppMail User Web Interface. The affected feature is the large file transfer (LFT).
This issue affects SeppMail: 15.0.2.1 and before
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Analysis
by VulDB Data Team • 05/18/2026
The vulnerability identified as CVE-2026-2743 represents a critical path traversal flaw within the SeppMail user web interface that enables attackers to achieve arbitrary file writing and subsequently execute remote code. This security weakness specifically impacts the large file transfer functionality, which serves as an entry point for malicious actors to manipulate the system's file structure. The vulnerability affects all versions of SeppMail up to and including version 15.0.2.1, making it a widespread concern for organizations utilizing this email server solution. The issue stems from inadequate input validation and sanitization mechanisms within the file upload process, allowing attackers to manipulate file paths and write content to arbitrary locations on the target system.
The technical exploitation of this vulnerability involves crafting malicious file upload requests that leverage path traversal sequences to bypass normal file system restrictions. Attackers can manipulate the file naming and destination parameters during the large file transfer process to write files to sensitive system directories such as web root folders, configuration files, or system binaries. This arbitrary file writing capability directly maps to CWE-22, which describes improper limitation of a pathname to a restricted directory, commonly known as path traversal or directory traversal attacks. The vulnerability's progression from file writing to remote code execution typically involves uploading malicious scripts or binaries that can be executed by the web server or system processes, thereby providing attackers with persistent access to the compromised system.
The operational impact of CVE-2026-2743 extends beyond simple data compromise, as it provides attackers with full system control through the execution of arbitrary code. Organizations running affected SeppMail versions face significant risk of unauthorized access, data exfiltration, system compromise, and potential lateral movement within their network infrastructure. The vulnerability's presence in the user web interface makes it particularly dangerous as it can be exploited by unauthenticated attackers, reducing the attack surface and increasing the likelihood of successful exploitation. From an attack chain perspective, this vulnerability aligns with ATT&CK technique T1059.007 for command and script interpreter, where attackers can execute code through uploaded malicious files, and T1078.004 for valid accounts, as the compromised system may be used to establish persistent access. The large file transfer feature represents a legitimate functionality that attackers can abuse to gain unauthorized system access.
Mitigation strategies for CVE-2026-2743 should prioritize immediate patching of affected SeppMail installations to version 15.0.2.2 or later, which contains the necessary security fixes. Organizations should implement input validation controls that sanitize all file paths and prevent directory traversal sequences from being processed during file upload operations. Network segmentation and access controls should be strengthened to limit exposure of the affected web interface to untrusted networks. Additionally, monitoring systems should be configured to detect unusual file upload patterns and suspicious file operations within the web server environment. Security teams should conduct thorough vulnerability assessments to identify any potential exploitation attempts and ensure proper log retention for forensic analysis. The remediation process must also include reviewing and updating security policies to address the specific threat vectors presented by this vulnerability, incorporating lessons learned into broader security program improvements and incident response procedures.