TLS server impersonation possible in Mikrotik RouterOS

Description

MikroTik RouterOS accepts malformed RSA/PKCS#1 v1.5 signatures during X.509 validation. 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. This issue affects only 7.x branch was fixed in versions: 7.23.4 (Long-term) and 7.24.2 (Stable)

Also Affects

Downstream vendors/products affected by this vulnerability

References

• https://cert.pl/en/posts/2026/09/mikrotik-routeros-cve(third-party-advisory)
• https://cert.pl/en/posts/2026/09/vulnerabilities-in-mikrotik-routeros-actively-exploited/(technical-description)
• https://npratley.net/reversing-mikrotiks-silent-patch-the-routeros-7-23-4-fix-they-wouldnt-explain/(exploit)
• https://mikrotik.com/supportsec/september-2026-vulnerability/(vendor-advisory)
• https://forum.mikrotik.com/t/7-23-4-long-term-is-released/272801(release-notes)
• https://forum.mikrotik.com/t/7-24-2-stable-is-released/272800(release-notes)

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