CVE-2026-29144 is a vulnerability identified in SEPPmail Secure Email Gateway prior to version 15.0.3, categorized under CWE-20 (Improper Input Validation). The issue arises because the product fails to correctly sanitize email subject fields when they contain Unicode lookalike characters. Attackers can exploit this by crafting email subjects that visually appear sanitized but actually contain malicious or forged security tags due to the use of Unicode characters that resemble standard ASCII characters. This bypasses the gateway's subject sanitization mechanisms, potentially allowing forged security tags to be inserted into emails. These forged tags can mislead recipients or automated security systems into trusting malicious emails or bypassing security checks. The vulnerability has a CVSS 4.0 base score of 7.8, reflecting its network attack vector (AV:N), low attack complexity (AC:L), no privileges or user interaction required (PR:N, UI:N), and a high scope impact (SI:H). The vulnerability affects confidentiality minimally but impacts integrity by allowing forged tags and potentially impacts availability slightly due to trust erosion. No known exploits have been reported in the wild as of the publication date. The vulnerability was reserved on March 4, 2026, and published on April 2, 2026. The lack of patch links suggests the fix is included in version 15.0.3, which users should upgrade to. The vulnerability is particularly relevant for organizations relying on SEPPmail Secure Email Gateway for secure email processing, as it undermines the trustworthiness of email subject sanitization and security tagging.

The primary impact of CVE-2026-29144 is on the integrity of email security mechanisms within organizations using SEPPmail Secure Email Gateway. By bypassing subject sanitization and forging security tags, attackers can cause malicious emails to appear legitimate or sanitized, increasing the risk of phishing, social engineering, or malware delivery. This can lead to compromised user credentials, data breaches, or the spread of malware within corporate networks. The vulnerability does not require authentication or user interaction, making it easier for remote attackers to exploit. The erosion of trust in email security tags can also impact automated security systems that rely on these tags for filtering or policy enforcement, potentially allowing malicious emails to bypass defenses. While confidentiality and availability impacts are limited, the overall effect on organizational security posture and user trust is significant. The scope is high as the vulnerability affects all instances of the product prior to version 15.0.3, potentially impacting any organization using this gateway for email security worldwide.

To mitigate CVE-2026-29144, organizations should immediately upgrade SEPPmail Secure Email Gateway to version 15.0.3 or later, where the input validation and subject sanitization issues are resolved. In addition to patching, organizations should implement enhanced email filtering rules that detect and flag suspicious Unicode characters in email subjects and headers, particularly those that resemble ASCII characters but differ in encoding. Security teams should monitor email logs for unusual patterns or forged security tags and consider deploying additional layers of email security such as DMARC, DKIM, and SPF to validate sender authenticity. User awareness training should emphasize caution with emails that have unusual subject lines or formatting. Network-level protections such as intrusion detection systems can be tuned to detect exploitation attempts targeting this vulnerability. Finally, organizations should maintain up-to-date threat intelligence feeds to stay informed about any emerging exploits targeting this vulnerability.