Threat Intelligence / CVE / CVE-2021-35394

CVE-2021-35394 — Realtek Rtl819x Jungle Software Development Kit

CISA KEV

CVSS v3.1 9.8 (CRITICAL) · EPSS 99.8% (higher than 99.9% of all scored CVEs) · Priority 9/10 · Published 2021-08-16

As of 2025-10-21, CVE-2021-35394 is a CRITICAL-severity vulnerability in Realtek Rtl819x Jungle Software Development Kit, CVSS v3.1 9.8, EPSS 99.8% (99.9th percentile). It is listed in the CISA Known Exploited Vulnerabilities catalog (added 2021-12-10), with a US federal remediation deadline of 2021-12-24. Threadlinqs Intelligence links 1 tracked threat campaign to CVE-2021-35394, most recently “Fodcha — Cross-Architecture DDoS Botnet Spreading via N-Day Exploits (CVE-2021-22205, CVE-2021-35394) and Telnet/SSH Brute-Force, Later Adding Ransom DDoS”.

Last updated: 2025-10-21

What is CVE-2021-35394?

Realtek Jungle SDK version v2.x up to v3.4.14B provides a diagnostic tool called 'MP Daemon' that is usually compiled as 'UDPServer' binary. The binary is affected by multiple memory corruption vulnerabilities and an arbitrary command injection vulnerability that can be exploited by remote unauthenticated attackers.

The record classifies CVE-2021-35394 under weakness class 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 1854 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): 99.8% probability of exploitation in the next 30 days, higher than 99.9% of all scored CVEs
CISA KEV: Listed since 2021-12-10, federal remediation deadline 2021-12-24
Threadlinqs priority: 9/10 — CISA KEV-listed, which Threadlinqs floors at 9
Published: 2021-08-16, last modified 2025-10-21

Is CVE-2021-35394 being exploited?

CISA added CVE-2021-35394 to the Known Exploited Vulnerabilities catalog on 2021-12-10, which means the agency holds evidence of exploitation in the wild; US federal civilian agencies had to remediate it by 2021-12-24 under BOD 22-01. Weaponised exploit code for CVE-2021-35394 is publicly available. 1 public proof-of-concept repository is tracked for this identifier. A ProjectDiscovery Nuclei detection template exists (javascript/cves/2021/CVE-2021-35394.yaml). It currently carries a trending score of 45 in the Threadlinqs vulnerability feed.

trickest/cve (trickest)

Affected products and versions

Realtek: Rtl819x Jungle Software Development Kit

How to fix CVE-2021-35394

The record marks a vendor fix as available for CVE-2021-35394. Patch reference: https://www.realtek.com/en/cu-1-en/cu-1-taiwan-en. Vendor advisory: https://www.realtek.com/en/cu-1-en/cu-1-taiwan-en. Because CVE-2021-35394 is KEV-listed, US federal civilian agencies were required to apply the vendor fix, or stop using the product, by 2021-12-24. Apply the vendor fix referenced above to every affected product listed in this record, then confirm the running version against the vendor advisory.

Threat activity tracking CVE-2021-35394

1 tracked threat in the Threadlinqs corpus references CVE-2021-35394, either in the campaign’s CVE list or as an indicator on the campaign record.

Fodcha — Cross-Architecture DDoS Botnet Spreading via N-Day Exploits (CVE-2021-22205, CVE-2021-35394) and Telnet/SSH Brute-Force, Later Adding Ransom DDoS — HIGH · 2026-06-10

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 2026-06-22. This product uses the NVD API but is not endorsed or certified by the NVD.

Other references

Full detection coverage & IOCs for threats exploiting CVE-2021-35394 are available via the Threadlinqs MCP server (Purple tier). View plans →

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