CVE-2021-20124
CVE-2021-20124 is a security flaw in DrayTek VigorConnect, routers for homes and small offices. Attackers can read files on DrayTek VigorConnect that should be out of reach 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 3 Sep 2024.[1]
DrayTek VigorConnect is in things households have: home and small-office routers, so the fix matters at home as much as at work. DrayTek has published a fix or advice.
Description
CISA calls it a path traversal in DrayTek VigorConnect. In its words: “Draytek VigorConnect contains a path traversal vulnerability in the file download functionality of the WebServlet endpoint. An unauthenticated attacker could leverage this vulnerability to download arbitrary files from the underlying operating system with root privileges.”[1]
The underlying weakness is path traversal (CWE-22), in MITRE’s list of common software weaknesses.[2]
It scores 7.5 out of 10 on the Common Vulnerability Scoring System, which rates it high, scored by NVD using CVSS 3.1.[2]
Affected versions
NVD’s record doesn’t list version ranges for it; DrayTek’s advisory has them[3]. CISA names the product as DrayTek VigorConnect.
Every device with DrayTek VigorConnect needs the update.
Exploitation
CISA added it to its catalog of known exploited vulnerabilities on 3 Sep 2024, 1,056 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 Sep 2024 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 96%. 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
DrayTek has published a fix or advice.[3] CISA’s required action: “Apply mitigations per vendor instructions or discontinue use of the product if mitigations are unavailable.”[1]
- Update DrayTek VigorConnect now.Open the router’s app, or its admin page in a browser, and look for a firmware update. Then turn on automatic updates, so the next fix arrives on its own.
- If the maker has stopped updating it, replace it.Routers stop getting fixes after a few years, and attackers keep a list of the ones that did. If there’s no newer firmware, it won’t be fixed.
Timeline
| Date | Event |
|---|---|
| The flaw is made public in the National Vulnerability Database, with a severity score of 7.5.[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 96%.[4] |
See also
Other DrayTek VigorConnect flaws
- CVE-2021-20123: path traversal ·
Other DrayTek flaws
- CVE-2024-12987, DrayTek Vigor Routers: OS command injection ·
- CVE-2020-15415, DrayTek Multiple Vigor Routers: OS command injection ·
- CVE-2020-8515, DrayTek Multiple Vigor Routers: multiple drayTek vigor routers web management page ·
Other path traversal flaws
- CVE-2025-61624, Fortinet products: path traversal ·
- CVE-2021-3199, ONLYOFFICE Docs: server path traversal ·
- CVE-2026-104286, Fortinet FortiMail: path traversal ·
- CVE-2026-93616, Check Point products: path traversal ·
- CVE-2026-66384, JFrog Artifactory: improper limitation of a pathname to a restricted directory ·
Added the same day
- CVE-2024-7262, Kingsoft WPS Office: path traversal ·
- CVE-2021-20123, DrayTek VigorConnect: path traversal ·
Every DrayTek flaw on CISA’s list · Everything added in September 2024
References
- ^ Cybersecurity and Infrastructure Security Agency. “Draytek VigorConnect Path Traversal Vulnerability”. Known Exploited Vulnerabilities Catalog, added 3 Sep 2024.
- ^ National Institute of Standards and Technology. “CVE-2021-20124 Detail”. National Vulnerability Database, published 13 Oct 2021.
- ^ DrayTek. Advisories and fixes: draytek.com.
- ^ FIRST. “Exploit Prediction Scoring System”. EPSS 0.959, percentile 99.9, 31 Oct 2026.
- CVE Program. “CVE-2021-20124”. 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.