RCE/DoS in widely deployed Siemens building/automation controllers; can disrupt facilities and operational infrastructure across organizations.
CVE-2021-31886
FTP USER buffer overflow in Siemens building controllers allows remote code execution or DoS.
Is CVE-2021-31886 being exploited?
Not confirmed. CVE-2021-31886 does not appear in CISA's Known Exploited Vulnerabilities catalog, which records only exploitation that has been observed and reported publicly. That is evidence of absence of a report, not evidence the flaw is unattacked. EPSS currently estimates a 3.0% probability of exploitation in the next 30 days.
How severe is CVE-2021-31886?
CVE-2021-31886 is rated Critical with a CVSS score of 9.8. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.
Is there a patch for CVE-2021-31886?
Yes. A fix has been recorded for CVE-2021-31886. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2021-31886 affect?
CVE-2021-31886 affects Siemens APOGEE PXC (Compact/Modular), Siemens APOGEE MBC/MEC, Siemens Desigo PXC series, Siemens TALON TC (Compact/Modular), and 1 further product or version. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2021-31886?
Apply Siemens updates immediately; block/limit FTP, isolate controllers, monitor logs.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Remote code execution or denial of service via crafted FTP USER command, enabling full control or outage of building controllers.
Immediate action required
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As published in the CVE Program record. A version outside these ranges is not a statement that it is unaffected — vendors sometimes understate a range, and distribution-backported builds carry upstream numbers that do not reflect what was patched into them.