No exploitation reportedFix available

CVE-2021-27391

Q: Is CVE-2021-27391 actively exploited?

Active exploitation of CVE-2021-27391 has not been confirmed. Its EPSS score was 3.4% on 2026-10-22, the estimated probability of exploitation in the next 30 days.

Q: What is the CVSS score for CVE-2021-27391?

CVE-2021-27391 has a CVSS v3 base score of 9.8 (CRITICAL severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

No exploitation reported by the sources we read.

Published2021-09-14
WeaknessCWE-120

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

Description

A vulnerability has been identified in APOGEE MBC (PPC) (P2 Ethernet) (All versions >= V2.6.3), APOGEE MEC (PPC) (P2 Ethernet) (All versions >= V2.6.3), APOGEE PXC Compact (BACnet) (All versions < V3.5.3), APOGEE PXC Compact (P2 Ethernet) (All versions >= V2.8), APOGEE PXC Modular (BACnet) (All versions < V3.5.3), APOGEE PXC Modular (P2 Ethernet) (All versions >= V2.8), TALON TC Compact (BACnet) (All versions < V3.5.3), TALON TC Modular (BACnet) (All versions < V3.5.3). The web server of affected devices lacks proper bounds checking when parsing the Host parameter in HTTP requests, which could lead to a buffer overflow. An unauthenticated remote attacker could exploit this vulnerability to execute arbitrary code on the device with root privileges.

Timeline

dates in UTC

2021-09-1411:15CVE publishedNVD

Observed activity

isMalicious corpus · updated 2026-10-23 18:48 UTC

Indicators tagged with this CVE, per day0 indicators over 7 days

Block these indicators

Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2021-27391?format=txt
CSV export: https://api.ismalicious.com/edl/cve/CVE-2021-27391?format=csv
TAXII collection of exploited CVEs
The EDL and CSV take an API key on the Pro plan.

Versions per branch

NVD

Siemens apogee mbc \(ppc\) \(p2 ethernet\) firmwareversion to verify

Branch	Affected	Fixed in	Source
2.6	≤ 2.6.3	no fix published	NVD

Siemens apogee mec \(ppc\) \(p2 ethernet\) firmwareversion to verify

Branch	Affected	Fixed in	Source
2.6	≤ 2.6.3	no fix published	NVD

Siemens apogee pxc bacnet automation controller firmwareversion to verify

Branch	Affected	Fixed in	Source
3.5	< 3.5.3	3.5.3	NVD

5 more products in the sources.

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Distribution builds and vendor advisories

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Vendor advisories

ICSA-21-257-07 CISA8 known affected
Siemens APOGEE and TALON
APOGEE MBC (PPC) (P2 Ethernet) · APOGEE MEC (PPC) (P2 Ethernet) · APOGEE PXC Compact (BACnet) · +5 more

Full record on NVD

Fix

Vendor fix CISA ICSA-21-257-07 · 4 productsUpdate to V3.5.3 or later version
Mitigation from the vendor CISA ICSA-21-257-07 · 8 productsPlease contact your local Siemens office for support
Mitigation from the vendor CISA ICSA-21-257-07 · 8 productsRestrict access to the device, especially to the web interface (80/tcp and 443/tcp), to trusted IP addresses only
Mitigation from the vendor CISA ICSA-21-257-07 · 8 productsDisable the integrated web server
No fix available, says the vendor CISA ICSA-21-257-07 · 4 productsCurrently no remediation is available

Advisories and patches

cert-portal.siemens.comPatch · Vendor Advisory

Detection

Nuclei template: none so far
Exploit-DB: no entry
Proof-of-concept repositories: none listed

Sources

CISA-ADPSSVC decisionnone2025-04-23
OpenCVESSVC decisionnone—
CISA-ADPCVSS 3.19.82025-04-23
NVDCVSS 3.19.8read 2026-10-23
NVDCVSS 2.010read 2026-10-23
CNAweakness (CWE)CWE-120read 2026-10-23
FIRST EPSSEPSS score3.4 %2026-10-22

Technical details

CVSS v3 Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Published: 2021-09-14
Last Modified: 2026-06-17
NVD status: Modified

Frequently asked questions

What is CVE-2021-27391?

Is CVE-2021-27391 actively exploited?

Active exploitation of CVE-2021-27391 has not been confirmed. Its EPSS score was 3.4% on 2026-10-22, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2021-27391?

CVE-2021-27391 has a CVSS v3 base score of 9.8 (CRITICAL severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

Running APOGEE MBC (PPC) (P2 Ethernet)? Hear about its next vulnerability

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