How severe is CVE-2021-25663?

CVE-2021-25663 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2021-25663 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (77th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-25663?

CVE-2021-25663 primarily affects Siemens Capital Vstar. In total, 4 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-25663?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2021-25663 published?

CVE-2021-25663 was published on 2021-04-22 and last updated on 2026-06-17.

CVE-2021-25663

CVE-2021-25663 is a high-severity vulnerability in Siemens Capital Vstar with a CVSS 3.x base score of 7.5. 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-835.

Key facts

Severity: High (CVSS 3.x base score 7.5)
CVSS v2: 5.0
CVSS v4: 8.7
EPSS exploit prediction: 2% (77th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-835
Affected product: Siemens Capital Vstar
Published: 2021-04-22
Last modified: 2026-06-17

Description

A vulnerability has been identified in Capital Embedded AR Classic 431-422 (All versions), Capital Embedded AR Classic R20-11 (All versions < V2303), Nucleus NET (All versions), Nucleus ReadyStart V3 (All versions < V2017.02.4), Nucleus ReadyStart V4 (All versions < V4.1.0), Nucleus Source Code (All versions including affected IPv6 stack). The function that processes IPv6 headers does not check the lengths of extension header options, allowing attackers to put this function into an infinite loop with crafted length values.

Frequently asked questions

What is CVE-2021-25663?: A vulnerability has been identified in Capital Embedded AR Classic 431-422 (All versions), Capital Embedded AR Classic R20-11 (All versions < V2303), Nucleus NET (All versions), Nucleus ReadyStart V3 (All versions < V2017.02.4), Nucleus ReadyStart V4 (All versions < V4.1.0), Nucleus Source Code (All versions including affected IPv6 stack). The function that processes IPv6 headers does not check the lengths of extension header options, allowing attackers to put this function into an infinite loop with crafted length values.
How severe is CVE-2021-25663?: CVE-2021-25663 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2021-25663 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (77th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-25663?: CVE-2021-25663 primarily affects Siemens Capital Vstar. In total, 4 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-25663?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2021-25663 published?: CVE-2021-25663 was published on 2021-04-22 and last updated on 2026-06-17.

References

Affected products (4)

cpe:2.3:a:siemens:capital_vstar:-:*:*:*:*:*:*:*
cpe:2.3:a:siemens:nucleus_net:*:*:*:*:*:*:*:*
cpe:2.3:a:siemens:nucleus_readystart:*:*:*:*:*:*:*:*
cpe:2.3:a:siemens:nucleus_source_code:-:*:*:*:*:*:*:*

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