CVE-2026-27445 is a cryptographic signature verification vulnerability affecting SEPPmail Secure Email Gateway versions before 15.0.1. The vulnerability arises from improper verification of PGP signatures, specifically failing to confirm that a signature was generated by the expected cryptographic key. This flaw corresponds to CWE-347, which describes improper verification of cryptographic signatures. In practice, this means that an attacker can craft a malicious email with a forged PGP signature that appears valid to the gateway, bypassing the intended cryptographic trust model. The vulnerability is remotely exploitable without requiring authentication or user interaction, as the gateway processes incoming emails over the network. The CVSS v4.0 base score is 6.9 (medium severity), reflecting the network attack vector, low attack complexity, no privileges required, no user interaction, and limited impact on integrity (partial compromise of signature trust). The scope is high, indicating that the vulnerability affects components beyond the immediate vulnerable code. No known exploits have been reported in the wild as of publication. The vulnerability undermines the fundamental security guarantees of PGP signatures, potentially allowing attackers to impersonate trusted senders, conduct phishing or social engineering attacks, or distribute malicious content under the guise of legitimate signed emails. The issue is resolved in SEPPmail Secure Email Gateway version 15.0.1 and later, where proper cryptographic signature verification is enforced.

The primary impact of CVE-2026-27445 is the compromise of email authenticity and integrity within organizations using vulnerable SEPPmail Secure Email Gateway versions. Attackers can spoof PGP signatures, making malicious emails appear as if they were signed by trusted entities. This can lead to successful phishing campaigns, social engineering attacks, and the delivery of malware or fraudulent instructions disguised as legitimate communications. The trust model of secure email is fundamentally weakened, potentially causing financial loss, data breaches, or operational disruption. Since the vulnerability can be exploited remotely without authentication or user interaction, it poses a significant risk to any organization relying on SEPPmail for secure email processing. The medium severity rating reflects that while confidentiality and availability are not directly impacted, the integrity and authenticity of communications are critically undermined. Organizations in sectors with high reliance on secure email, such as finance, government, healthcare, and critical infrastructure, are particularly vulnerable to targeted attacks leveraging this flaw.

To mitigate CVE-2026-27445, organizations should promptly upgrade SEPPmail Secure Email Gateway to version 15.0.1 or later, where the cryptographic signature verification logic has been corrected. Until the upgrade is applied, administrators should implement additional email security controls such as enhanced monitoring for anomalous signed emails, strict email filtering policies, and user awareness training to recognize suspicious messages. Deploying complementary security solutions like DMARC, DKIM, and SPF can help reduce the risk of spoofed emails, although they do not directly address PGP signature verification. Network segmentation and limiting exposure of the email gateway to untrusted networks can reduce attack surface. Regularly auditing email gateway logs for unusual signature validation failures or unexpected key usage can aid in early detection of exploitation attempts. Organizations should also review their incident response plans to address potential phishing or spoofing incidents arising from this vulnerability.