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PatchSiren cyber security CVE debrief

CVE-2026-2743 SeppMail CVE debrief

A critical arbitrary file write vulnerability in SeppMail's Large File Transfer (LFT) feature enables unauthenticated remote code execution through path traversal during file upload operations. The vulnerability affects SeppMail versions 15.0.2.1 and earlier, with a CVSS 4.0 score of 10.0 (Critical). The attack vector is network-accessible with low attack complexity, requiring no privileges or user interaction. Successful exploitation allows complete compromise of confidentiality, integrity, and availability across both the vulnerable component and subsequent systems. The vulnerability was disclosed on March 5, 2026, and modified in the NVD on May 19, 2026. Multiple related CVEs (CVE-2026-7864, CVE-2026-44127, CVE-2026-44128) were identified in the same research effort by InfoGuard Labs and reported through Swiss NCSC.

Vendor
SeppMail
Product
Unknown
CVSS
CRITICAL 10
CISA KEV
Not listed in stored evidence
Original CVE published
2026-03-05
Original CVE updated
2026-05-19
Advisory published
2026-03-05
Advisory updated
2026-05-19

Who should care

Organizations operating SeppMail secure email gateways; security teams managing email security infrastructure; incident responders tracking email gateway compromises; compliance officers evaluating data loss prevention controls

Technical summary

The SeppMail User Web Interface contains a path traversal vulnerability in its Large File Transfer (LFT) upload functionality. Insufficient input validation on filename parameters allows attackers to traverse directory structures and write files to arbitrary locations on the underlying filesystem. This primitive enables remote code execution through placement of executable code in web-accessible directories or system locations processed by the operating system. The vulnerability is exploitable without authentication, presenting maximum severity risk for exposed instances.

Defensive priority

CRITICAL

Recommended defensive actions

  • Immediately upgrade SeppMail to a version newer than 15.0.2.1 per vendor release notes
  • Restrict network access to SeppMail User Web Interface LFT endpoints to authorized administrative hosts only
  • Implement Web Application Firewall (WAF) rules to detect and block path traversal sequences (../, ..%2f, etc.) in file upload requests
  • Enable comprehensive file upload validation including whitelist-based filename character restrictions and server-side path canonicalization
  • Monitor for anomalous file system writes outside designated upload directories and unexpected process executions from web service contexts
  • Review and rotate credentials for any SeppMail-integrated systems following potential compromise
  • Assess related CVEs CVE-2026-7864, CVE-2026-44127, and CVE-2026-44128 for coordinated remediation

Evidence notes

Vulnerability confirmed through NVD CPE criteria (cpe:2.3:a:seppmail:seppmail:*:*:*:*:*:*:*:*) with version bound ≤15.0.2.1. CWE-22 (Path Traversal) and CWE-434 (Unrestricted Upload of File with Dangerous Type) classified. CVSS 4.0 vector confirms network attack vector, no required privileges, and high impacts across all security properties. Source references include vendor release notes and third-party security research from InfoGuard Labs.

Official resources

2026-03-05T07:16:14.670Z