How severe is CVE-2021-25677?

CVE-2021-25677 has a CVSS 3.x base score of 5.3, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity low, and availability none.

Is CVE-2021-25677 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (61st percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-25677?

CVE-2021-25677 primarily affects Siemens Simotics Connect 400 Firmware. In total, 5 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-25677?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

When was CVE-2021-25677 published?

CVE-2021-25677 was published on 2021-04-22 and last updated on 2026-06-17.

CVE-2021-25677

CVE-2021-25677 is a medium-severity vulnerability in Siemens Simotics Connect 400 Firmware with a CVSS 3.x base score of 5.3. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-330.

Key facts

Severity: Medium (CVSS 3.x base score 5.3)
CVSS v2: 5.0
EPSS exploit prediction: 1% (61st percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-330
Affected product: Siemens Simotics Connect 400 Firmware
Published: 2021-04-22
Last modified: 2026-06-17

Description

A vulnerability has been identified in APOGEE PXC Compact (BACnet) (All versions < V3.5.5), APOGEE PXC Compact (P2 Ethernet) (All versions < V2.8.20), APOGEE PXC Modular (BACnet) (All versions < V3.5.5), APOGEE PXC Modular (P2 Ethernet) (All versions < V2.8.20), Nucleus NET (All versions), Nucleus ReadyStart V3 (All versions < V2017.02.3), Nucleus ReadyStart V3 (All versions < V2017.02.4), Nucleus ReadyStart V4 (All versions < V4.1.0), Nucleus Source Code (Versions including affected DNS modules), SIMOTICS CONNECT 400 (All versions < V0.5.0.0), SIMOTICS CONNECT 400 (All versions >= V0.5.0.0 < V1.0.0.0), TALON TC Compact (BACnet) (All versions < V3.5.5), TALON TC Modular (BACnet) (All versions < V3.5.5). The DNS client does not properly randomize DNS transaction IDs. That could allow an attacker to poison the DNS cache or spoof DNS resolving.

Frequently asked questions

What is CVE-2021-25677?: A vulnerability has been identified in APOGEE PXC Compact (BACnet) (All versions < V3.5.5), APOGEE PXC Compact (P2 Ethernet) (All versions < V2.8.20), APOGEE PXC Modular (BACnet) (All versions < V3.5.5), APOGEE PXC Modular (P2 Ethernet) (All versions < V2.8.20), Nucleus NET (All versions), Nucleus ReadyStart V3 (All versions < V2017.02.3), Nucleus ReadyStart V3 (All versions < V2017.02.4), Nucleus ReadyStart V4 (All versions < V4.1.0), Nucleus Source Code (Versions including affected DNS modules), SIMOTICS CONNECT 400 (All versions < V0.5.0.0), SIMOTICS CONNECT 400 (All versions >= V0.5.0.0 < V1.0.0.0), TALON TC Compact (BACnet) (All versions < V3.5.5), TALON TC Modular (BACnet) (All versions < V3.5.5). The DNS client does not properly randomize DNS transaction IDs. That could allow an attacker to poison the DNS cache or spoof DNS resolving.
How severe is CVE-2021-25677?: CVE-2021-25677 has a CVSS 3.x base score of 5.3, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity low, and availability none.
Is CVE-2021-25677 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (61st percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-25677?: CVE-2021-25677 primarily affects Siemens Simotics Connect 400 Firmware. In total, 5 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-25677?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2021-25677 published?: CVE-2021-25677 was published on 2021-04-22 and last updated on 2026-06-17.

References

Affected products (5)

cpe:2.3:o:siemens:simotics_connect_400_firmware:*:*:*:*:*:*:*:*
cpe:2.3:a:siemens:nucleus_net:*:*:*:*:*:*:*:*
cpe:2.3:a:siemens:nucleus_readystart_v3:*:*:*:*:*:*:*:*
cpe:2.3:a:siemens:nucleus_readystart_v4:*:*:*:*:*:*:*:*
cpe:2.3:a:siemens:nucleus_source_code:-:*:*:*:*:*:*:*

More vulnerabilities in Siemens Simotics Connect 400 Firmware

CVE-2019-13939 — High (CVSS 7.1): A vulnerability has been identified in APOGEE MEC/MBC/PXC (P2) (All versions < V2.8.2), APOGEE PXC Compact (BACnet)…
CVE-2020-27738 — Medium (CVSS 6.5): A vulnerability has been identified in APOGEE PXC Compact (BACnet) (All versions < V3.5.5), APOGEE PXC Compact (P2…
CVE-2020-27737 — Medium (CVSS 6.5): A vulnerability has been identified in APOGEE PXC Compact (BACnet) (All versions < V3.5.5), APOGEE PXC Compact (P2…
CVE-2020-27736 — Medium (CVSS 6.5): A vulnerability has been identified in APOGEE PXC Compact (BACnet) (All versions < V3.5.5), APOGEE PXC Compact (P2…

All CVEs affecting Siemens Simotics Connect 400 Firmware →

Other CWE-330 (Use of Insufficiently Random Values) vulnerabilities

CVE-2023-22601 — Critical (CVSS 10.0): InHand Networks InRouter 302, prior to version IR302 V3.5.56, and InRouter 615, prior to version…
CVE-2026-25072 — Critical (CVSS 9.8): XikeStor SKS8310-8X Network Switch firmware versions 1.04.B07 and prior contain a predictable session identifier…
CVE-2026-27755 — Critical (CVSS 9.8): SODOLA SL902-SWTGW124AS firmware versions through 200.1.20 contain a weak session identifier generation vulnerability…
CVE-2026-27637 — Critical (CVSS 9.8): FreeScout is a free help desk and shared inbox built with PHP's Laravel framework. Prior to version 1.8.206,…
CVE-2025-64097 — Critical (CVSS 9.8): NervesHub is a web service that allows users to manage over-the-air (OTA) firmware updates of devices in the field. A…
CVE-2025-4607 — Critical (CVSS 9.8): The PSW Front-end Login & Registration plugin for WordPress is vulnerable to Privilege Escalation in all versions up…

Browse all CWE-330 (Use of Insufficiently Random Values) vulnerabilities →