Treck TCP/IP stack Out-of-Bounds Read Vulnerability (CVE-2020-11899)
Published In CISA KEV since Sources: CVE.org, Schneider Electric
What is affected, what to do
The Treck TCP/IP stack before 6.0.1.66 has an IPv6 Out-of-bounds Read.
The vulnerability is being actively exploited; treat it as a priority. Update Treck TCP/IP stack IPv6 to version 6.0.1.66. Immediate actions, mitigation and detection rules are in the runbook below.
- Affected
- Treck TCP/IP stack IPv6
lt *..6.0.1.66
- Treck TCP/IP stack IPv6
- Fixed in
- Treck TCP/IP stack IPv6
6.0.1.66
- Treck TCP/IP stack IPv6
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Metrics
5.4
Priority
XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.
Source: NVD, CVSS v3
5.4
CVSS v3
Severity Medium on the scale from 0 to 10.
Source: CVE.org, Schneider Electric
18.4 %
EPSS score
Elevated — model estimates 10-50% exploitation likelihood.
Source: FIRST EPSS, percentile 97.2
Show all metrics
- Severity
- Critical
Priority (0–325)
The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first?
Read in glossary- 202.63 Methodology
Exploit maturity
An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack.
Read in glossary- actively exploited
XIEM Effective CVSS
XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command.
Read in glossary- 5.4 Methodology
CVSS v3
CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.
Read in glossary- 5.4
EPSS score
The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“.
Read in glossary- 18.4 %
- Elevated — model estimates 10-50% exploitation likelihood.
EPSS percentile
The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking.
Read in glossary- 97.2
- Critical — this CVE ranks in the top fifth of all CVEs scored today (rank ≥ 80%).
KEV status
The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.
Read in glossary- Actively exploited
- Published
In CISA KEV since
The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.
Read in glossary
Response and mitigation
Why act now?
Prioritisation rationale
CVE-2020-11899 is one of the "Ripple20" vulnerabilities in the Treck TCP/IP stack, added to CISA KEV because of the stack's extremely broad deployment across OT, IoT, medical, and thin-client environments where patching is slow and network segmentation is often absent. The CVSS 3.1 score of 5.4 (AV:A) reflects the adjacent-network requirement, but in flat OT networks or unsegmented thin-client deployments that precondition is routinely met by any attacker who has reached the LAN. The EPSS score of 18.56 % (97th percentile) places this CVE among the most likely to be actively targeted relative to all published CVEs — a strong signal to prioritise remediation even without a CISA ransomware-campaign flag. Organisations running Dell Wyse Thin Clients or any Treck-embedded device in KRITIS-relevant infrastructure should treat this as high priority, weighting the difficult patch logistics of embedded firmware against the high exploitation probability.
Runbook step 1
Immediate response (0-24 h)
- Update the Treck TCP/IP stack to version 6.0.1.66 or later — patch available directly from Treck Inc.; verify the exact build number in the vendor advisory at treck.com.
- Apply Dell firmware updates for all affected Wyse Thin Client models (5030, 5050 AIO, 7030) via the Dell Security Advisory for CVE-2020-11899 — confirm target firmware version in the Dell advisory before deployment.
- Disable IPv6 on all affected devices where it is not operationally required — this eliminates the attack vector entirely until patching is complete.
- Isolate affected devices into a dedicated VLAN and block inbound IPv6 traffic from untrusted network segments at the nearest Layer-2/Layer-3 boundary (ACL: DROP ip6 from untrusted sources to affected segment).
- Build a complete inventory of all assets running the Treck stack — pay particular attention to OT, medical, and industrial environments where Treck is embedded in firmware and patching cycles are long.
Runbook step 2
Mitigation layers
- Network segmentation: Place affected devices behind a firewall that drops all inbound ICMPv6 and IPv6 packets originating outside explicitly trusted management sources; deny IPv6 transit between user VLANs and OT/thin-client segments.
- IPS/IDS signature: Deploy a Suricata rule targeting malformed IPv6 headers — flag packets where the IPv6 Payload Length field exceeds the actual captured packet size, or where Extension Header lengths are inconsistent:
alert ipv6 any any -> $TRECK_HOSTS any (msg:"CVE-2020-11899 malformed IPv6 header"; sid:2020118990;). - RA-Guard / DHCPv6 snooping: Enable IPv6 Router Advertisement Guard on all switches connected to Treck-device segments to prevent attackers from injecting IPv6 into otherwise IPv4-only environments.
- Endpoint hardening: Disable IPv6 at the OS or firmware level where feasible. On Windows hosts: set
HKLM\SYSTEM\CurrentControlSet\Services\Tcpip6\Parameters\DisabledComponents = 0xFF. For embedded devices, consult the manufacturer's hardening guide. - Least privilege / access control: Restrict management interfaces of affected Wyse Thin Clients to a dedicated management VLAN; ensure no direct reachability from end-user or guest networks.
Runbook step 3
Detection rules
- Network telemetry (Zeek/Suricata): Alert on IPv6 packets with inconsistent header lengths or unexpected Extension Header chains destined for Treck-device segments — use the Suricata SID above as a starting point and tune thresholds per environment.
- Flow data (SIEM/SPL): Detect unexpected IPv6 flows to assets that should be IPv4-only:
index=netflow ip_version=6 dest_ip IN($TRECK_ASSET_LIST) | stats count by src_ip, dest_ip, _time— any result warrants investigation. - Availability correlation: A spike in ICMP Unreachable responses or TCP RSTs from Treck devices following IPv6 traffic may indicate a crash or reboot caused by the out-of-bounds read — alert on > 3 such events within 60 seconds from the same source IP.
- Thin-client management platform: Monitor Dell Wyse Management Suite (or equivalent) for unexpected device disconnections or reboots as an indicator of successful DoS exploitation.
- Windows Event Log: On Windows hosts running Treck-based applications, correlate Event ID 1000 (Application Error) and 1001 (Windows Error Reporting) for crashes in Treck-related processes or services.
Detection rules
No NEOSEC detection rule is available for this vulnerability yet.
Classification under NIS2 and CRA
Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.
NIS2
NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.
Read in glossary- Actively exploited: treat the vulnerability as a priority in vulnerability handling under Art. 21(2)(e) NIS2. If it is exploited in your environment, check the reporting obligation under Art. 23 (early warning within 24 hours).
CRA
The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.
Read in glossary- Since 11.09.2026, manufacturers of affected products with digital elements must report actively exploited vulnerabilities under Art. 14 CRA, with an early warning within 24 hours via ENISA's single reporting platform.
ISO/IEC 27001
ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.
Read in glossary- Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.
Description
The Treck TCP/IP stack before 6.0.1.66 has an IPv6 Out-of-bounds Read.
Source: NVD (NIST), CISA KEV Catalog, cvelistv5, schneider_csaf
Affected products
The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| treck | tcp\/ip |
|
|
| Schneider Electric | NMC3 AOS |
|
|
Vendors and products
Affected operating systems
| Family | Vendor | Product | Version |
|---|---|---|---|
| Other | dell | wyse_5030_firmware | — |
| Other | dell | wyse_5050_all-in-one_firmware | — |
| Other | dell | wyse_7030_firmware | — |
Public exploit references
Publicly reported proof-of-concepts, exploit modules and detection templates for this vulnerability. NEOSEC links to the original sources only and does not provide any exploit code.
| Source | Reference | Maturity | Published |
|---|---|---|---|
| CISA KEV Catalog | CISA Known Exploited Vulnerability (opens in a new tab)cisa.gov | actively exploited |
References & sources
- cwe.mitre.orgdata/definitions/125.htmlx_refsource_MISC, Technical description
- kb.cert.orgvuls/id/257161x_refsource_MISC, Mitigation, Third-party advisory, US government resource
- treck.comx_refsource_MISC, Product, Vendor advisory
- jsof-tech.comvulnerability-disclosure-policyx_refsource_MISC, Broken link, Third-party advisory
- intel.comcontent/www/us/en/security-center/advisory/intel-sa-00295.htmlx_refsource_CONFIRM, Third-party advisory
- kb.cert.orgVU#257161Third-party advisory, x_refsource_CERT-VN, Third-party advisory, US government resource
- jsof-tech.comripple20x_refsource_MISC, Broken link, Exploit, Third-party advisory
- tools.cisco.com20200617 Multiple Vulnerabilities in Treck IP Stack Affecting Cisco Products: June 2020Vendor advisory, x_refsource_CISCO, Third-party advisory
- arubanetworks.comassets/alert/ARUBA-PSA-2020-006.txtx_refsource_CONFIRM, Broken link, Third-party advisory
- security.netapp.comadvisory/ntap-20200625-0006x_refsource_CONFIRM, Third-party advisory
- dell.comsupport/article/de-de/sln321836/dell-response-to-the-ripple20-v…x_refsource_MISC, Third-party advisory
- cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2020-11899government-resource, US government resource
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<a href="https://intel.neosec.eu/en/cve/CVE-2020-11899"><img src="https://intel.neosec.eu/badge/cve/CVE-2020-11899.svg?lang=en" alt="CVE-2020-11899 – NEOSEC Intel" height="20"></a>