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No exploitation reportedFix available

CVE-2021-25664

No exploitation reported by the sources we read.

  • Published2021-04-22
  • WeaknessCWE-835

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 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 the Hop-by-Hop extension header in IPv6 packets and its options lacks any checks against the length field of the header, allowing attackers to put the function into an infinite loop by supplying arbitrary length values.

Timeline

dates in UTC
  1. 2021-04-2221:15CVE publishedNVD

Observed activity

isMalicious corpus · updated 2026-10-23 21:37 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-2021-25664?format=txt
  • CSV export: https://api.ismalicious.com/edl/cve/CVE-2021-25664?format=csv
  • TAXII collection of exploited CVEs
  • The EDL and CSV take an API key on the Pro plan.

Versions per branch

NVD
Siemens capital vstar
BranchAffectedFixed in
—all versionsno fix published
Siemens nucleus net
BranchAffectedFixed in
—all versionsno fix published
Siemens nucleus readystart v3
BranchAffectedFixed in
2017.2< 2017.02.42017.02.4

2 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-21-103-05 CISA6 known affected

    Siemens Nucleus Products IPv6 Stack

    Capital Embedded AR Classic 431-422 · Capital Embedded AR Classic R20-11 · Nucleus NET · +3 more

Full record on NVD

Fix

  1. Vendor fix CISA ICSA-21-103-05 · 1 productUpdate to V2017.02.4 or later version
  2. Vendor fix CISA ICSA-21-103-05 · 1 productUpdate to V2303 or later version
  3. Vendor fix CISA ICSA-21-103-05 · 1 productUpdate to V4.1.0 or later version
  4. Vendor fix CISA ICSA-21-103-05 · 1 productContact customer support to receive patch and update information
  5. Mitigation from the vendor CISA ICSA-21-103-05 · 1 productContact customer support or your local Nucleus Sales team for mitigation advice
  6. Mitigation from the vendor CISA ICSA-21-103-05 · 2 productsDisable IPv6 functionality, if feature not used, by deselecting the TcpIpIpV6General/IpV6Enabled Pre-Compile configuration option

Advisories and patches

Detection

Nuclei template
none so far
ProjectDiscovery
Exploit-DB
no entry
Exploit-DB
Proof-of-concept repositories
none listed
PoC-in-GitHub

Sources

  • CNACVSS 4.08.7read 2026-10-23
  • CNACVSS 3.17.5read 2026-10-23
  • NVDCVSS 3.17.5read 2026-10-23
  • NVDCVSS 2.05read 2026-10-23
  • CNAweakness (CWE)CWE-835read 2026-10-23
  • FIRST EPSSEPSS score1.9 %2026-10-22

Technical details

CVSS v3 Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CVSS 4.0 vector
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Published
2021-04-22
Last Modified
2026-06-17
NVD status
Modified

Frequently asked questions

What is CVE-2021-25664?

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 the Hop-by-Hop extension header in IPv6 packets and its options lacks any checks against the length field of the header, allowing attackers to put the function into an infinite loop by supplying arbitrary length values.

Is CVE-2021-25664 actively exploited?

Active exploitation of CVE-2021-25664 has not been confirmed. Its EPSS score was 1.9% on 2026-10-22, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2021-25664?

CVE-2021-25664 has a CVSS v3 base score of 7.5 (HIGH severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

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