CVE-2026-67278: Forged TLS Certificates in MikroTik RouterOS 7

CVE-2026-67278 is a critical (CVSS 9.1) signature verification flaw in MikroTik RouterOS 7. The device accepts malformed RSA signatures, which lets an attacker impersonate TLS servers. Fixed in 7.23.6 (long term) and 7.24.3 (stable). Releases 7.23.4 and 7.24.2 had an incomplete fix, so update again.

What's affected

• Product: MikroTik RouterOS, the 7.x branch only. CERT Polska lists vulnerable versions as 7.0.0 below 7.23.6 and 7.24 below 7.24.3.
• Fixed versions: 7.23.6 (long term) and 7.24.3 (stable).
• Incomplete fix: releases 7.23.4 and 7.24.2 included an incomplete fix for this CVE, so devices on them need another update.
• Weakness: CWE-347 improper verification of cryptographic signature.
• Severity: CVSS 3.1 9.1, no privileges, with confidentiality and integrity impact.
• Exploitation: the CISA KEV flag in the record is false. CERT Polska reports active exploitation of a different pair of flaws from the same disclosure, an SSH chain it calls MikroTrick, and its notes do not say that this CVE was part of the observed attacks.

How to check if you're exposed

On the router, read the version and the device state:

/system/resource/print
/system/device-mode/print

The first command shows the RouterOS version. CERT Polska says the second shows a flagged marker that the fixed releases set when they find signs of unauthorized changes. The absence of the marker does not prove a device is clean.

Compare the version with 7.23.6 on the long term channel or 7.24.3 on the stable channel. Devices on 7.23.4 or 7.24.2 are still affected by this CVE. Also check which services face the internet: SSH, WWW and the bandwidth test server, per CERT Polska's guidance.

What to do now

1. Inventory RouterOS devices and their versions and channels.
2. Update to 7.23.6 (long term) or 7.24.3 (stable) or later. Update devices that are on 7.23.4 or 7.24.2 again.
3. Block SSH, web and bandwidth test access from outside trusted management networks.
4. After updating, check the logs for the compromise message and the flagged marker, and review the configuration for unknown users, scripts, scheduler tasks, proxies and tunnels.
5. Until you can update, avoid starting TLS connections from the router and avoid its built in SSH clients, especially across untrusted networks.
6. If compromise is possible, isolate the device and save logs and configuration before any reset.

Why it matters

RSA signatures using PKCS#1 version 1.5 have a strict format. A verifier that accepts loosely formatted signatures can be fooled, and this risk grows when the public exponent is very small. CERT Polska says RouterOS accepted malformed signatures and that its trust store held a root certificate with a public exponent of 3. With that combination, an attacker who controls or redirects an outbound connection can use the root's public certificate, without its private key, to forge a trusted intermediate and issue certificates for any hostname. The same permissive check weakens RSA based SSH authentication.

The affected traffic is the router's own outbound TLS, such as fetching updates or talking to services, so the exposure depends on what the router connects to and who can sit on that path. The advisory also warns that other flaws in this disclosure are under active attack, and that is a good reason to treat this whole update as urgent. A second lesson is process: two releases carried an incomplete fix, so confirm the exact version and not just that you updated once.

Quick check

Sources

• CERT Polska: vulnerabilities in MikroTik RouterOS
• CERT Polska: critical RouterOS vulnerabilities being actively exploited
• Gold record for CVE-2026-67278

Last reviewed: 19 October 2026.