CVE-2020-29557
CVE-2020-29557 is a security flaw in D-Link DIR-825 R1 Devices, routers for homes and small offices. Attackers can run their own code on D-Link DIR-825 R1 Devices 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 Nov 2021.[1]
D-Link DIR-825 R1 Devices is in things households have: home and small-office routers, so the fix matters at home as much as at work.
Description
CISA calls it a buffer overflow in D-Link DIR-825 R1 Devices. In its words: “D-Link DIR-825 R1 devices contain a buffer overflow vulnerability in the web interface that may allow for remote code execution.”[1]
The CVE record adds: “An issue was discovered on D-Link DIR-825 R1 devices through 3.0.1 before 2020-11-20. A buffer overflow in the web interface allows attackers to achieve pre-authentication remote code execution.”[2]
The underlying weakness is memory buffer error (CWE-119), 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. CISA names the product as D-Link DIR-825 R1 Devices.
Every device with D-Link DIR-825 R1 Devices needs the update.
Exploitation
CISA added it to its catalog of known exploited vulnerabilities on 3 Nov 2021, 278 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 3 May 2022 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 56%. That’s in the top 1% of the flaws it scores.[3]
CISA assesses it as automatable: attackers can run it against many targets at once.
CISA doesn’t say who was attacked, or how.
Fix
CISA’s required action: “Apply updates per vendor instructions.”[1]
- Update D-Link DIR-825 R1 Devices 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 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 56%.[3] |
See also
Other D-Link flaws
- CVE-2025-29635, D-Link DIR-823X: command injection ·
- CVE-2022-37055, D-Link Routers: buffer overflow ·
- CVE-2022-40799, D-Link DNR-322L: download of code without integrity check ·
- CVE-2020-25079, D-Link DCS-2530L and DCS-2670L Devices: DCS-2530L and DCS-2670L command injection ·
- CVE-2020-25078, D-Link DCS-2530L and DCS-2670L Devices: unspecified ·
Other memory buffer error flaws
- CVE-2026-88779, Citrix NetScaler: improper restriction of operations within the bounds of a memory buffer ·
- CVE-2026-88772, Citrix NetScaler: improper restriction of operations within the bounds of a memory buffer ·
- CVE-2026-88771, Citrix NetScaler: improper input validation ·
- CVE-2026-8452, Citrix NetScaler ADC and NetScaler Gateway: improper restriction of operations within the bounds of a memory buffer ·
- CVE-2009-3459, Adobe Acrobat and Reader: heap-based buffer overflow ·
Added the same day
- CVE-2021-42258, BQE BillQuick Web Suite: SQL injection ·
- CVE-2021-42013, Apache HTTP Server: path traversal ·
- CVE-2021-41773, Apache HTTP Server: path traversal ·
- CVE-2021-40539, Zoho ManageEngine: aDSelfService plus authentication bypass ·
- CVE-2021-40444, Microsoft MSHTML: remote code execution ·
Every D-Link flaw on CISA’s list · Everything added in November 2021
References
- ^ Cybersecurity and Infrastructure Security Agency. “D-Link DIR-825 R1 Devices Buffer Overflow Vulnerability”. Known Exploited Vulnerabilities Catalog, added 3 Nov 2021.
- ^ National Institute of Standards and Technology. “CVE-2020-29557 Detail”. National Vulnerability Database, published 29 Jan 2021.
- ^ FIRST. “Exploit Prediction Scoring System”. EPSS 0.557, percentile 99.0, 31 Oct 2026.
- CVE Program. “CVE-2020-29557”. 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.