CVE-2026-67277: MikroTik RouterOS bandwidth-test server leaks memory and crashes

Exploited in the wild High 8.8 EPSS 1.6% MikroTik RouterOS

The RouterOS bandwidth-test (btest) server accepts a related connection before the main session has logged in. An unauthenticated attacker can use it to leak uninitialised kernel memory and, through an integer underflow, make the router restart. CISA added it to the Known Exploited Vulnerabilities catalog on 10 September 2026. Fixed in RouterOS 6.49.21, 7.23.4 and 7.24.2.

What do these terms mean? CVE · CVSS score · exploited (KEV) · EPSS · backported fix · all terms

What to do now

  1. Check whether you run MikroTik RouterOS and which version (commands below).
  2. Install the fixed version for your system: see “Patch it” below.
  3. Installing a RouterOS update always reboots the router. On RouterBOARD hardware, run /system routerboard upgrade afterwards and reboot a second time so the matching RouterBOOT firmware is loaded. Plan for two short outages and make sure you have out-of-band or local access in case the router does not come back.
  4. If you cannot patch today, apply the temporary mitigation below and patch as soon as possible.
  5. Because this flaw is being exploited, also check the server for signs of compromise.

Affected and fixed versions

Affected:

Fixed in:

Am I affected?

/system resource print   # version, architecture-name, board-name
/system package update print   # channel, installed-version, latest-version
/system routerboard print   # current-firmware vs upgrade-firmware (not on CHR/x86)
/ip service print   # which management services are enabled, and from where
/tool bandwidth-server print   # enabled: yes means the btest server listens (TCP 2000)

Patch it

Use the commands for your system. Distribution packages often keep an older version number with the fix backported, so compare with the fixed package versions in the table below, not only with the upstream version.

Built from source
# RouterOS CLI (works on v6 and v7; v7 also accepts /system/package/update/...)
# Current releases as of 3 Nov 2026: 7.25 (stable), 7.24.6 (long-term), 6.49.23 (RouterOS 6)
/system backup save name=pre-update
/export file=pre-update
/system package update set channel=long-term   # or stable
/system package update check-for-updates
/system package update print   # status should say: New version is available
/system package update install   # downloads, installs and REBOOTS the router
# after it is back up:
/system resource print   # confirm the new version
/system routerboard upgrade   # RouterBOARD only: new RouterBOOT firmware
/system reboot   # REBOOTS again to load the firmware

General update steps for every system are on the Linux and Unix & BSD pages; after updating, see which services to restart.

If you cannot patch yet

Look for signs of exploitation

CISA 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). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines.

https://mikrotik.com/supportsec/september-2026-vulnerability/ ; BOD 26-04: https://www.cisa.gov/news-events/directives/bod-26-04-prioritizing-security-updates-based-risk ; Forensics Triage Requirements: https://www.cisa.gov/news-events/directives/bod-26-04-implementation-guidance-prioritizing-security-updates-based-risk ; https://nvd.nist.gov/vuln/detail/CVE-2026-67277

Related vulnerabilities

Sources

Page generated automatically from official sources on 2026-11-03 18:05 UTC and reviewed by an editor. Always confirm with your vendor's advisory.