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CVE-2026-67278: TLS server impersonation possible in Mikrotik RouterOS

• Severity: critical (CVSS 9.1 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.3% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2026-09-05 · updated 2026-09-25
• Weakness: CWE-347

Description

MikroTik RouterOS accepts malformed RSA/PKCS#1 v1.5 signatures across RSA-based services, including TLS/X.509 certificate validation and SSH host-key authentication. Because its trust store includes an e=3 root CA, an attacker controlling or redirecting an outbound RouterOS TLS connection can use the root’s public certificate - without its private key - to forge a trusted intermediate and issue certificates for arbitrary hostnames, enabling TLS server impersonation. The same permissive verification also undermines RSA-based SSH authentication. This issue affects only 7.x branch was fixed in versions: 7.23.6 (Long-term) and 7.24.3 (Stable). Releases 7.23.4 and 7.24.2 included an incomplete fix.

Affected products

• MikroTik RouterOS: from 7.0 before 7.23.6; from 7.24 before 7.24.3 — fixed in 7.23.6, 7.24.3

How to fix

Upgrade to a fixed version: MikroTik RouterOS 7.23.6, 7.24.3. Check the vendor advisory for mitigations.

References

• https://cert.pl/en/posts/2026/09/mikrotik-routeros-cve
• https://cert.pl/en/posts/2026/09/vulnerabilities-in-mikrotik-routeros-actively-exploited/
• https://forum.mikrotik.com/t/7-23-6-long-term-is-released/273139
• https://forum.mikrotik.com/t/7-24-3-stable-is-released/273138
• https://mikrotik.com/supportsec/september-2026-vulnerability/
• https://npratley.net/reversing-mikrotiks-silent-patch-the-routeros-7-23-4-fix-they-wouldnt-explain/

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