# CVE-2021-36380 — Sunhillo Sureline

**CISA KEV**

> As of 2025-10-21, CVE-2021-36380 is a CRITICAL-severity vulnerability in Sunhillo Sureline, CVSS v3.1 9.8, EPSS 97.6% (99.9th percentile). It is listed in the CISA Known Exploited Vulnerabilities catalog (added 2024-03-05), with a US federal remediation deadline of 2024-03-26. Threadlinqs Intelligence links 2 tracked threat campaigns to CVE-2021-36380, most recently “ClingSTUN Linux Backdoor Turns Unpatched IoT Devices Into Proxy Nodes via Public STUN Infrastructure”.

**Last updated:** 2025-10-21

## What is CVE-2021-36380?

Sunhillo SureLine before 8.7.0.1.1 allows Unauthenticated OS Command Injection via shell metacharacters in ipAddr or dnsAddr /cgi/networkDiag.cgi.

The record classifies CVE-2021-36380 under weakness class [CWE-78](https://intel.threadlinqs.com/cwe/CWE-78). Its CVSS v3 base vector states that the flaw is reachable remotely over the network, needs no prior authentication, needs no user interaction, and has high impact on confidentiality, integrity, availability. 1 affected-product entry is recorded, across 1 vendor, listed below. The identifier was first published 1898 days ago.

## Severity and exploitation probability

- **CVSS v3.1 base score:** 9.8 — CRITICAL (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **EPSS (FIRST):** 97.6% probability of exploitation in the next 30 days, higher than 99.9% of all scored CVEs
- **CISA KEV:** Listed since 2024-03-05, federal remediation deadline 2024-03-26
- **Threadlinqs priority:** 9/10 — CISA KEV-listed, which Threadlinqs floors at 9
- **Published:** 2021-08-13, last modified 2025-10-21

## Is CVE-2021-36380 being exploited?

CISA added CVE-2021-36380 to the Known Exploited Vulnerabilities catalog on 2024-03-05, which means the agency holds evidence of exploitation in the wild; US federal civilian agencies had to remediate it by 2024-03-26 under BOD 22-01. Weaponised exploit code for CVE-2021-36380 is publicly available. 1 public proof-of-concept repository is tracked for this identifier. A ProjectDiscovery Nuclei detection template exists (`http/cves/2021/CVE-2021-36380.yaml`). It currently carries a trending score of 50 in the Threadlinqs vulnerability feed.

- [trickest/cve](https://github.com/trickest/cve/blob/main/2021/CVE-2021-36380.md) (trickest)

## Affected products and versions

- **Sunhillo**: Sureline

## How to fix CVE-2021-36380

Because CVE-2021-36380 is KEV-listed, US federal civilian agencies were required to apply the vendor fix, or stop using the product, by 2024-03-26. No vendor patch reference has been recorded for CVE-2021-36380 in the tracked sources. Follow the references below for a fix, and treat the products listed above as exposed until the vendor states otherwise.

## Threat activity tracking CVE-2021-36380

2 tracked threats in the Threadlinqs corpus reference CVE-2021-36380, either in the campaign’s CVE list or as an indicator on the campaign record.

- [ClingSTUN Linux Backdoor Turns Unpatched IoT Devices Into Proxy Nodes via Public STUN Infrastructure](https://intel.threadlinqs.com/threat/TL-2026-2934) — HIGH · 2026-10-05
- [Cling IoT botnet masquerades as Google STUN traffic for C2, exploiting Realtek Jungle SDK CVE-2021-35394](https://intel.threadlinqs.com/threat/TL-2026-2857) — CRITICAL · 2026-10-03

## Sources

Enriched from CVE.org, NVD, FIRST EPSS, CISA KEV, GitHub Security Advisories, public proof-of-concept repositories, ProjectDiscovery Nuclei. Last verified by Threadlinqs on 2026-10-10. This product uses the NVD API but is not endorsed or certified by the NVD.

**Other references**

- [sunhillo.com](https://www.sunhillo.com/product/sureline/)
- [research.nccgroup.com](https://research.nccgroup.com/2021/07/26/technical-advisory-sunhillo-sureline-unauthenticated-os-command-injection-cve-2021-36380/)

Canonical: https://intel.threadlinqs.com/cve/CVE-2021-36380
Full detection coverage and IOCs for threats exploiting CVE-2021-36380 via the Threadlinqs MCP server (Purple tier): https://intel.threadlinqs.com/mcp