CVE-2026-67278

MikroTik RouterOS 7.x improperly verifies RSA/PKCS#1 v1.5 signatures when validating X.509 certificate chains, accepting malformed signatures (CWE-347, Improper Verification of Cryptographic Signature). Because the RouterOS trust store includes a root CA whose public key uses the small exponent e=3, an attacker who can control or redirect one of the router's outbound TLS connections (for example via a network man-in-the-middle position, DNS hijacking, or a compromised upstream path) can forge an intermediate CA signed with the root's public key, without ever holding its private key, and mint trusted certificates for arbitrary hostnames. This lets the attacker impersonate TLS servers the router connects to, with low confidentiality and integrity impact per the CVSS 4.0 score of 6.3 (medium), which reflects the network vector, no privileges required, but a high attack requirement of holding such a network position. Any deployment running RouterOS 7.x before 7.23.4 (Long-term) or 7.24.2 (Stable) is affected, spanning home/SOHO, enterprise, and ISP/WISP infrastructure; the 6.x branch is not listed as affected. No public proof-of-concept is known, the issue is not in CISA's KEV, and EPSS gives a 0.2% probability of exploitation within 30 days, although related headlines note other MikroTik flaws have recently been chained to hack routers.

What to do: Upgrade RouterOS 7.x to 7.23.4 (Long-term track) or 7.24.2 (Stable track). Until patched, reduce the chance an attacker can sit on the router's outbound TLS path by hardening DNS resolvers, avoiding untrusted upstream networks, and restricting management-plane exposure, since exploitation requires controlling or redirecting an outbound connection. Given other RouterOS flaws have recently been chained in router hijacks, prioritize patching internet-exposed and ISP/WISP infrastructure devices.