CVE-2021-35394
CVE-2021-35394 is a security flaw in Realtek Jungle Software Development Kit (SDK). Attackers can run their own code on Realtek Jungle Software Development Kit (SDK) from anywhere, without logging in. The US Cybersecurity and Infrastructure Security Agency (CISA) added it to its catalog of flaws known to be used in attacks on 10 Dec 2021.[1]
Realtek Jungle Software Development Kit (SDK) is in things households have, such as phones, computers, browsers and everyday apps, so the fix matters at home as much as at work. Realtek has published a fix or advice.
Description
CISA calls it a jungle SDK remote code execution in Realtek Jungle Software Development Kit (SDK). In its words: “RealTek Jungle SDK contains multiple memory corruption vulnerabilities which can allow an attacker to perform remote code execution.”[1]
The CVE record adds: “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.”[2]
The underlying weakness is OS command injection (CWE-78), CWE-138, in MITRE’s list of common software weaknesses.
It scores 9.8 out of 10 on the Common Vulnerability Scoring System, which rates it critical, scored by NVD using CVSS 3.1.[2]
Affected versions
NVD’s record doesn’t list version ranges for it; Realtek’s advisory has them[3]. CISA names the product as Realtek Jungle Software Development Kit (SDK).
Every device with Realtek Jungle Software Development Kit (SDK) needs the update.
Exploitation
CISA added it to its catalog of known exploited vulnerabilities on 10 Dec 2021, 116 days after it was made public. CISA lists a flaw only when it has reliable evidence of it being exploited, and gave US federal agencies until 24 Dec 2021 to fix it.[1]
FIRST’s Exploit Prediction Scoring System, which estimates how likely a flaw is to be used in attacks in the next 30 days from what it sees across the internet, puts it at over 99%. That’s in the top 1% of the flaws it scores.[4]
CISA assesses it as automatable: attackers can run it against many targets at once.
CISA doesn’t say who was attacked, or how.
Fix
Realtek has published a fix or advice.[3] CISA’s required action: “Apply updates per vendor instructions.”[1]
- Update Realtek Jungle Software Development Kit (SDK) now.Install the latest update from Realtek on every device that has it, and restart when asked. Then turn on automatic updates, so the next fix arrives on its own.
- If there’s no update, stop using it.CISA’s advice when a flaw being used in attacks has no fix is to stop using the product until it does.
Timeline
| Date | Event |
|---|---|
| The flaw is made public in the National Vulnerability Database, with a severity score of 9.8.[2] | |
| CISA adds it to its catalog of flaws known to be used in attacks.[1] | |
| CISA’s deadline for US government agencies to fix it.[1] | |
| FIRST puts the odds of it being used in attacks in the next 30 days at over 99%.[4] |
See also
Other Realtek flaws
- CVE-2014-8361, Realtek SDK: improper input validation ·
- CVE-2021-35395, Realtek AP-Router SDK: buffer overflow ·
Other OS command injection flaws
- CVE-2026-110447, Collabora Online – Built-in CODE Server: online – built-in CODE server OS command injection ·
- CVE-2026-106931, EG Secure Solutions SiteGuard Server Edition: OS command injection ·
- CVE-2026-83549, SonicWall SMA1000 Appliances: OS command injection ·
- CVE-2026-49869, Kestra OSS: OSS OS command injection ·
- CVE-2026-73570, Synacor Zimbra Collaboration Suite (ZCS): OS command injection ·
Added the same day
- CVE-2021-44515, Zoho Desktop Central: authentication bypass ·
- CVE-2021-44228, Apache Log4j2: remote code execution ·
- CVE-2021-44168, Fortinet FortiOS: arbitrary file download ·
- CVE-2020-8816, Pi-hole AdminLTE: remote code execution ·
- CVE-2020-17463, Fuel CMS: SQL injection ·
Every Realtek flaw on CISA’s list · Everything added in December 2021
References
- ^ Cybersecurity and Infrastructure Security Agency. “Realtek Jungle SDK Remote Code Execution Vulnerability”. Known Exploited Vulnerabilities Catalog, added 10 Dec 2021.
- ^ National Institute of Standards and Technology. “CVE-2021-35394 Detail”. National Vulnerability Database, published 16 Aug 2021.
- ^ Realtek. Advisories and fixes: realtek.com.
- ^ FIRST. “Exploit Prediction Scoring System”. EPSS 0.999, percentile 100.0, 31 Oct 2026.
- CVE Program. “CVE-2021-35394”. The official CVE record.
This article is built from CISA’s catalog (version 2026.10.30), NVD’s record and FIRST’s scores, kept in HARD’s database and checked every morning. The plain English is HARD’s.