CVE-2026-67277
CVE-2026-67277 is a security flaw in MikroTik RouterOS, the operating system on MikroTik’s routers. Attackers can get into MikroTik RouterOS without a valid password. The US Cybersecurity and Infrastructure Security Agency (CISA) added it to its catalog of flaws known to be used in attacks on 10 Sep 2026.[1]
MikroTik RouterOS is business software or equipment. Most families won’t have it, but attackers break into it to get inside companies, and from there to what those companies hold about their customers, patients and staff. Fixed in version 7.24.2, 7.23.4 and 6.49.21 of RouterOS.
Description
CISA calls it a missing authentication for critical function in MikroTik RouterOS. In its words: “MikroTik RouterOS contains a missing authentication for critical function vulnerability which allows kernel memory disclosure and denial of service in the btest service.”[1]
The CVE record adds: “RouterOS accepts a "related" btest connection before the corresponding primary session has completed authentication. An unauthenticated client can use this state to start an IPv4 UDP test. With "random-data=false", the sender transmits an uninitialized tail from a kernel packet buffer. A separate unchecked, inverted packet-size interval causes unsigned integer underflow, anomalously large fragmented output, and can restart the RouterOS kernel. This issue was fixed in versions: 6.49.21 (Long-term), 7.23.4 (Long-term) and 7.24.2 (Stable)”[2]
The underlying weakness is missing authentication (CWE-306), in MITRE’s list of common software weaknesses.
It scores 8.2 out of 10 on the Common Vulnerability Scoring System, which rates it high, scored by NVD using CVSS 3.1.[2]
Affected versions
NVD’s record lists these fixed versions: in each line, everything before the version shown is affected.[2]
| Product | Fixed in |
|---|---|
| RouterOS | 7.24.2 |
| RouterOS | 7.23.4 |
| RouterOS | 6.49.21 |
Most families won’t have MikroTik RouterOS; it’s for whoever looks after IT at work.
Exploitation
CISA added it to its catalog of known exploited vulnerabilities on 10 Sep 2026, 5 days after it was made public. CISA lists a flaw only when it has reliable evidence of it being exploited, and gave US federal agencies until 13 Sep 2026 to fix it.[1]
FIRST’s Exploit Prediction Scoring System, which estimates how likely a flaw is to be used in attacks in the next 30 days from what it sees across the internet, puts it at 2%. That’s in the top 25% of the flaws it scores.[4]
CISA assesses it as automatable: attackers can run it against many targets at once.
CISA doesn’t say who was attacked, or how.
Fix
MikroTik has published a fix or advice.[3] CISA’s required action: “Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes).”[1]
- Check whether you use it.MikroTik RouterOS is business software or equipment, so most families won’t have it. If you run a business, or work from home on company equipment, ask whoever looks after your IT.
- Send this page to your IT person.Ask them to confirm it’s fixed (fixed in version 7.24.2, 7.23.4 and 6.49.21 of RouterOS), or not in use. CISA gave US government agencies until 13 Sep 2026 to fix it.
- If it can’t be fixed, take it offline.CISA’s advice when there’s no fix is to stop using the product, or take it off the internet, until there is one.
You can’t fix someone else’s server, but you can watch for what follows a break-in like this: a breach notice, a password reset you didn’t ask for, or a scam message that knows things it shouldn’t. HARD watches for those for you and your family.
Timeline
| Date | Event |
|---|---|
| The flaw is made public in the National Vulnerability Database, with a severity score of 8.2.[2] | |
| CISA adds it to its catalog of flaws known to be used in attacks.[1] | |
| CISA’s deadline for US government agencies to fix it.[1] | |
| FIRST puts the odds of it being used in attacks in the next 30 days at 2%.[4] |
See also
Other MikroTik RouterOS flaws
- CVE-2026-67279: improper enforcement of behavioral workflow ·
- CVE-2026-86060: improper neutralization of argument delimiters in a command ·
- CVE-2018-7445: stack-based buffer overflow ·
- CVE-2018-14847: router OS directory traversal ·
Other missing authentication flaws
- CVE-2026-111357, Ivanti Connect Secure: missing authentication for critical function ·
- CVE-2026-81578, PaperCut NG/MF: missing authentication for critical function ·
- CVE-2026-72529, TrueConf Server: missing authentication for critical function ·
- CVE-2026-56164, Microsoft SharePoint Server: missing authentication for critical function ·
- CVE-2026-20253, Splunk Enterprise: missing authentication for critical function ·
Added the same day
- CVE-2026-86060, MikroTik RouterOS: improper neutralization of argument delimiters in a command ·
Every MikroTik flaw on CISA’s list · Everything added in September 2026
References
- ^ Cybersecurity and Infrastructure Security Agency. “MikroTik RouterOS Missing Authentication for Critical Function Vulnerability”. Known Exploited Vulnerabilities Catalog, added 10 Sep 2026.
- ^ National Institute of Standards and Technology. “CVE-2026-67277 Detail”. National Vulnerability Database, published 5 Sep 2026.
- ^ MikroTik. Advisories and fixes: mikrotik.com, cert.pl, forum.mikrotik.com, forum.mikrotik.com, forum.mikrotik.com.
- ^ FIRST. “Exploit Prediction Scoring System”. EPSS 0.016, percentile 75.2, 31 Oct 2026.
- CVE Program. “CVE-2026-67277”. The official CVE record.
This article is built from CISA’s catalog (version 2026.10.30), NVD’s record and FIRST’s scores, kept in HARD’s database and checked every morning. The plain English is HARD’s.