CVE-2026-84411: Integer Underflow (CVSS 9.8)

Description

The web management service in affected RouterOS versions contains an integer underflow in its HTTP request body handling that is reachable before authentication. This can be leveraged by an unauthenticated network attacker to achieve arbitrary code execution as root, or to cause a denial of service, using a single crafted request.

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CVSS v3.1 Score

9.8

CRITICAL

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

EPSS — Exploit Prediction

0.0095

Probability of exploitation

0.60%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-191 CWE-191

References

Other References

https://github.com/cisagov/CSAF/blob/develop/csaf_files/OT/white/2026/icsa-26-272-06.json https://mikrotik.com/download https://www.cisa.gov/news-events/ics-advisories/icsa-26-272-06

Frequently Asked Questions

What is CVE-2026-84411? +

The web management service in affected RouterOS versions contains an integer underflow in its HTTP request body handling that is reachable before authentication. This can be leveraged by an unauthenticated network attacker to achieve arbitrary code execution as root, or to cause a denial of service, using a single crafted request. It has a CVSS v3.1 base score of 9.8 (CRITICAL).

How severe is CVE-2026-84411? +

CVE-2026-84411 has a CVSS v3.1 score of 9.8 out of 10, rated CRITICAL. This is a critical vulnerability that should be patched immediately. The EPSS score is 0.0095, placing it in the 1th percentile for exploitation probability.

How do I check if I'm vulnerable to CVE-2026-84411? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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