Security readout for executives and security teams
Plain-English summary
CVE-2021-21960 is a critical remote code execution risk in Sealevel Systems SeaConnect 370W v1.3.34. A malformed network packet sent to its LLMNR functionality can overflow stack memory. For executives, treat exposed affected devices as high-priority operational technology risk because compromise could allow full attacker control of the device.
Executive priority
Prioritize this as urgent if affected devices are deployed and network reachable. The score and impact justify rapid inventory, segmentation, and vendor remediation review, even though active exploitation is not confirmed by the provided sources.
Technical view
The issue is a CWE-121 stack-based buffer overflow in the SeaConnect 370W v1.3.34 LLMNR functionality. CVSS 3.0 is 10.0 with network attack vector, low complexity, no privileges, no user interaction, changed scope, and high confidentiality, integrity, and availability impact.
Likely exposure
Exposure is likely limited to organizations running Sealevel Systems SeaConnect 370W v1.3.34 with LLMNR functionality reachable on a network. The provided sources do not identify other affected versions, CPEs, or dependent products.
Exploitation context
The sources state that a specially crafted network packet can trigger remote code execution. The CVE is not listed as KEV in the provided bundle, and no cited source here confirms active exploitation in the wild.
Researcher notes
Evidence supports unauthenticated network-triggered RCE in SeaConnect 370W v1.3.34 LLMNR handling. The bundle does not provide exploit-in-the-wild evidence, affected-version range beyond v1.3.34, or a named patch level, so avoid broader claims.
Mitigation direction
- Identify any SeaConnect 370W devices and confirm firmware version 1.3.34.
- Check Sealevel and Talos guidance for fixed firmware or vendor-recommended mitigations.
- Restrict network access to affected devices, especially LLMNR-reachable segments.
- Isolate confirmed affected devices from untrusted networks until remediated.
- Monitor for unexpected traffic to affected device discovery services.
Validation and detection
- Review asset inventory for Sealevel Systems SeaConnect 370W deployments.
- Confirm device firmware versions through approved administrative channels.
- Map whether LLMNR functionality is reachable from user, guest, or external networks.
- Verify firewall and segmentation rules limit access to affected devices.
- Document remediation status and any vendor guidance gaps.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-121: Exact CWE lookup
Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupExecution behavior lookup
The CVE wording references code or command execution, so execution technique review may help defensive triage. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.
Open ATT&CK lookupCVE-2021-21960 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- Critical
- CVSS
- 10 (3.0)
- Known Exploited
- No
- Published
Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H3.96Primary CVE scoreVulnerability scoring details
Base CVSS 3.0 score
10CriticalVector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
Source materials
- CVE List V5 sourceCVE List V5
- https://talosintelligence.com/vulnerability_reports/TALOS-2021-1389CVE reference · x_refsource_MISC
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Stack-based Buffer Overflow
Stack-based Buffer Overflow represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.