When a security "shield" becomes a backdoor: Critical flaws threaten enterprise email gateways

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In the world of technology, security tools are often viewed as robust shields protecting an organization's digital assets. However, a worrying reality has emerged when the defensive system itself becomes a gateway for malicious actors.

Recently, researchers uncovered a series of critical weaknesses within the SEPPMail Secure E-Mail Gateway - a solution widely trusted by enterprises to filter, encrypt, and secure internal email communications.

Turning a protective shield into a hacker's access point

Instead of blocking threats from the internet, these newly found flaws transform the system into a lucrative "backdoor" for cybercriminals. Attackers can exploit these gaps to compromise the system, intercept and read all email traffic passing through the gateway, covertly install persistent remote control tools, and take over servers without needing any valid login credentials.

*A series of serious vulnerabilities have just been discovered within SEPPMail Secure E-Mail Gateway.*

According to experts, at least 7 security flaws have been identified. Among them, the most dangerous threat allows unauthorized actors to write arbitrary files directly onto the system and execute malicious code remotely, completely bypassing identity verification.

To pull this off, attackers only need to send malicious requests via the web interface to overwrite or modify system configuration files. They then force the logging service (syslog) to reload this new configuration, silently opening a reverse shell (a connection back to the attacker's machine) to discreetly gain full control over the device.

A closer look at the discovered vulnerabilities

Beyond the threat of full remote control, this chain of weaknesses opens up several other dangerous exploitation paths for unauthenticated attackers, including:

Viewing and deleting arbitrary files on the server.
Bypassing standard login checks to access administrative functions.
Running remote control commands.
Leaking environment variables, which often store sensitive system configuration data.

Here is the detailed list of the identified vulnerability codes:

CVE-2026-2743 (CVSS Severity Score: 10): A path traversal flaw located in the Large File Transfer (LFT) feature of the SeppMail user web interface. This allows attackers to write arbitrary files to the system, paving the way for Remote Code Execution (RCE).
CVE-2026-7864 (CVSS Score: 6.9): An information disclosure flaw that leaks sensitive system environment variables through an unauthenticated endpoint in the new GINA interface.
CVE-2026-44125 (CVSS Score: 9.3): A lack of authentication checks across multiple endpoints in the new GINA interface, allowing unauthenticated remote attackers to access functions that should require a valid login session.
CVE-2026-44126 (CVSS Score: 9.2): An untrusted data deserialization flaw. Attackers can send a specially crafted serialized object to force the system to execute malicious code without authentication.
CVE-2026-44127 (CVSS Score: 8.8): An unauthenticated path traversal vulnerability in the /api.app/attachment/preview endpoint. It permits remote attackers to read arbitrary local files or trigger file deletions within target directories under the privileges of the "api.app" process.
CVE-2026-44128 (CVSS Score: 9.3): An eval injection vulnerability within the /api.app/template feature. Because the system passes the user-supplied upldd parameter directly into Perl's eval() function without data validation or filtering, attackers can execute remote code without logging in.
CVE-2026-44129 (CVSS Score: 8.3): Improper handling of special components in the template engine. This allows remote attackers to execute arbitrary template expressions, potentially leading to remote code execution depending on which template plugins are enabled.

Severe impacts on enterprise security

The reason this chain of weaknesses translates into a security disaster is due to SEPPMail’s strategic position within the corporate network architecture. This gateway stands directly between all internal email traffic and the outside internet.

Doanh nghiệp cần nhanh chóng thực hiện các biện pháp phòng thủ — *Businesses need to quickly implement defensive measures.*

If this gatekeeper is compromised, attackers essentially hold a "master key" to manipulate the organization through highly dangerous activities:

Monitoring and reading the emails of all employees.
Eavesdropping on confidential internal communications.
Stealing all valuable document attachments.
Harvesting credentials or triggering unauthorized password reset processes.
Turning the gateway itself into a launchpad to attack deeper into the enterprise's internal network.

Urgent recommendations for organizations

To prevent the risk of valuable data leaks, the manufacturer has released patched, secure versions. Enterprises must quickly check and upgrade their SEPPMail systems to the following versions:

15.0.2.1
15.0.3
15.0.4

In addition to immediate software updates, experts recommend that system administrators thoroughly review access logs. Pay close attention to any unusual requests directed at API endpoints or file upload modules to promptly detect signs of intrusion.

For more detailed information regarding this vulnerability discovery, please refer to the original reporting on The Hacker News and Zeros Day.