CVE-2021-27391

Severity: critical (CVSS 9.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 3.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2021-09-14 · updated 2026-06-17
Weakness: CWE-120

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.

Affected products

Siemens Apogee Mbc (Ppc) (P2 Ethernet) Firmware: through 2.6.3
Siemens Apogee Mec (Ppc) (P2 Ethernet) Firmware: through 2.6.3
Siemens Apogee Pxc Bacnet Automation Controller Firmware: before 3.5.3 — fixed in 3.5.3
Siemens Apogee Pxc Compact (P2 Ethernet) Firmware: through 2.8
Siemens Apogee Pxc Modular (Bacnet) Firmware: before 3.5.3 — fixed in 3.5.3
Siemens Apogee Pxc Modular (P2 Ethernet) Firmware: through 2.8
Siemens Talon Tc Compact (Bacnet) Firmware: before 3.5.3 — fixed in 3.5.3
Siemens Talon Tc Modular (Bacnet) Firmware: before 3.5.3 — fixed in 3.5.3

How to fix

Upgrade to a fixed version: Siemens Apogee Pxc Bacnet Automation Controller Firmware 3.5.3; Siemens Apogee Pxc Modular (Bacnet) Firmware 3.5.3; Siemens Talon Tc Compact (Bacnet) Firmware 3.5.3; Siemens Talon Tc Modular (Bacnet) Firmware 3.5.3. Check the vendor advisory for mitigations.

References

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