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1Repair Windows errors before they cause bigger problems2Scan for outdated or missing drivers - takes under a minute3Clear out junk files and repair common Windows errorsRouterOS’s SSH authorized-key check omitted the RSA public exponent, creating CVE-2026-67276. CERT Polska says attackers used this flaw as part of the broader MikroTrick vulnerability chain against routers with SSH reachable from public networks. The exponent flaw is serious, but it is not, by itself, the separate rekey flaw CERT describes as enabling unauthenticated command execution.
What did MikroTik’s SSH key check miss?
When checking an offered RSA key against a user’s authorized key, RouterOS compared the key type and modulus but did not compare the public exponent, according to CERT Polska’s MikroTrick analysis. The exponent is part of an RSA public key, so leaving it out meant the check did not establish that the offered key matched the authorized key in full.
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CERT says an attacker who knew the target username and authorized RSA modulus could supply a key with an exponent of one. RouterOS then verified the signature using the client-supplied key. That could allow the attacker to forge a signature and open an SSH command channel as the target account without possessing its corresponding private key.
This is a public-key authentication flaw, not a password bypass. CERT Polska assigned it CVE-2026-67276 and a CVSS severity score of 9.2 in 2026. The score describes vulnerability severity; it is not a count or estimate of affected routers.
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How CVE-2026-67276 fits into MikroTrick
MikroTrick is CERT Polska’s name for a chain of RouterOS vulnerabilities. CERT reported active exploitation of devices with SSH reachable from public networks. The three issues described in the chain have distinct roles:
| CVE | Role in the chain |
|---|---|
| CVE-2026-67276 | SSH authorized-key comparison omitted the RSA public exponent, enabling the described public-key authentication bypass. |
| CVE-2026-86060 | Crafted usernames could manipulate privileges. |
| CVE-2026-67279 | An SSH rekey-state flaw; CERT describes this separate flaw in the chain as enabling unauthenticated command execution. |
Do not treat CVE-2026-67276 alone as the complete unauthenticated takeover chain. CERT’s account is that attackers combined vulnerabilities; the exponent omission concerns authentication as a target account, while the rekey flaw is a separate part of the chain.
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Which RouterOS versions contain the fixes?
MikroTik’s security bulletin lists fixes for the September 2026 issues in RouterOS 7.24.3, 7.23.6, and 6.49.21, or later applicable releases. Select the fixed release for your device’s RouterOS branch and check the bulletin for the current release before upgrading.
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Random freezes, missing sound and display glitches usually trace back to one bad driver. Find and replace yours safely.Free scan · under a minuteThe bulletin also warns that the earlier fixes for CVE-2026-67278 in RouterOS 7.24.2 and 7.23.4 were incomplete. The complete fix is in 7.24.3 and 7.23.6. This correction concerns CVE-2026-67278; it is a reason to verify the exact branch and release rather than assume that any earlier update resolved every issue in the September incident.
What to do if your router may be exposed or compromised
1. Reduce exposure while preparing to update
Update promptly to the fixed release that applies to your branch. If you cannot update immediately, CERT Polska recommends restricting or disabling SSH, WebFig, and bandwidth-test access from outside trusted management networks. These are temporary exposure controls, not a substitute for installing the fix. CERT also advises against initiating TLS or built-in SSH client connections from an unpatched device over untrusted paths.
2. Review logs and configuration
After securing the management services, check logs and configuration for changes you do not recognize. CERT advises looking for unknown users, scripts, scheduler tasks, proxy servers, tunnels, and other unrecognized changes. It lists these log artifacts as indicators to investigate:
login failure for user -2 from <ip> via sshuser <name> added by ssh:-2@<ip>- A privileged user named
ops
These indicators call for investigation; they are not, by themselves, a complete account of what happened on a router.
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3. Treat the “Flagged” marker as a warning, not an all-clear test
CERT’s check can mark selected traces as “Flagged.” A marker is meaningful evidence that warrants investigation, but the check examines only selected traces. CERT cautions: “The absence of the marker does not rule out an earlier compromise.”
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- FAST & CONVENIENT LOGIN: Plug in your YubiKey 5 via USB and tap it to authenticate. No batteries, no internet connection, and no extra fees required.
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4. If compromise is suspected, preserve evidence before recovery
CERT recommends isolating the router and preserving logs and configuration before resetting it. Restore from a trusted configuration, then change passwords, keys, and other secrets. Do not blindly restore a backup from a device that may have been compromised.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Why public exposure matters
CERT Polska confirmed exploitation against devices whose SSH service was reachable from public networks. That makes exposure of management services a practical risk factor: an internet-reachable SSH service gave attackers a path to target. A CVSS score does not indicate how many devices were exposed or compromised, and no source-backed population figure is established here.
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