CVE-2021-20090

CRITICALNVD 9.89.8—
EchelonGraph scoreHIGH confidence

Score elevated to 9.8 because this CVE is listed on the CISA Known Exploited Vulnerabilities catalog (added 2021-11-03), indicating real-world exploitation has been confirmed by US federal agencies. NVD baseline CVSS 9.8 retained for reference. Confidence: HIGH.

Triggered by: CISA KEV (actively exploited)
Sources: cisa_kev, epss, ghsa, nvd
Trending — 3 sources updated this weekExploited in the wild
9.8EG
EchelonGraph verdictPatch nowTreat as an emergency — this is being exploited.
  • Actively exploited in the wild (CISA-KEV)
CISA-KEV: ExploitedEPSS PROB: 100%CVSS: 9.8Exploit: cisa kev · ssvc active · epss top5pct · epss high · public exploitExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

A path traversal vulnerability in the web interfaces of Buffalo WSR-2533DHPL2 firmware version <= 1.02 and WSR-2533DHP3 firmware version <= 1.24 could allow unauthenticated remote attackers to bypass authentication.

CVSS v3
9.8
EG Score
9.8(high)
EG Risk
99(Act)
EG Risk 99/100SSVC: Act

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity98% × 45%
Exploitation100% × 40%
Automatability100% × 15%
Action: Fix now — active exploitation, automatable, high impact.
EPSS PROB
100%
EPSS %ILE
100%
KEV
⚠ Exploited

Published

April 29, 2021

Last Modified

November 3, 2025

Advisory Details (4)

Auto-updated Sep 24, 2026
⚠️ Active exploitation confirmed. Patch available. Sources: cert, cisa.
cisa Patch Available🔴 Active Exploitation

Known Exploited Vulnerabilities Catalog | CISA

Known Exploited Vulnerabilities Catalog | CISA. Listed in CISA Known Exploited Vulnerabilities catalog.

https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-20090
generic🟡 PoC Available

Multiple Vulnerabilities in Buffalo and Arcadyan manufactured routers - Research Advisory | Tenable®

https://www.tenable.com/security/research/tra-2021-13
generic🔴 Active Exploitation

Arcadyan-Based Routers and Modems Under Active Exploitation | SecPod

https://www.secpod.com/blog/arcadyan-based-routers-and-modems-under-active-exploitation/
cert

VU#914124 - Arcadyan-based routers and modems vulnerable to authentication bypass

https://www.kb.cert.org/vuls/id/914124

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 45× in last 7d / 189× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

Showing the most recent 100 of 714 total refreshes for this CVE.

  1. 2026-09-25 14:55 UTCCISA KEV update
  2. 2026-09-25 14:11 UTCGHSA enrichment
  3. 2026-09-25 09:54 UTCGHSA enrichment
  4. 2026-09-25 05:37 UTCGHSA enrichment
  5. 2026-09-25 01:20 UTCGHSA enrichment
  6. 2026-09-24 21:03 UTCGHSA enrichment
  7. 2026-09-24 19:31 UTCCISA KEV update
  8. 2026-09-24 16:46 UTCGHSA enrichment
  9. 2026-09-24 12:29 UTCGHSA enrichment
  10. 2026-09-24 08:11 UTCGHSA enrichment
  11. 2026-09-24 03:55 UTCGHSA enrichment
  12. 2026-09-23 23:38 UTCGHSA enrichment
  13. 2026-09-23 19:20 UTCGHSA enrichment
  14. 2026-09-23 15:03 UTCGHSA enrichment
  15. 2026-09-23 10:47 UTCGHSA enrichment
  16. 2026-09-23 06:30 UTCGHSA enrichment
  17. 2026-09-23 02:13 UTCGHSA enrichment
  18. 2026-09-22 21:56 UTCGHSA enrichment
  19. 2026-09-22 19:36 UTCCISA KEV update
  20. 2026-09-22 17:39 UTCGHSA enrichment
  21. 2026-09-22 13:21 UTCGHSA enrichment
  22. 2026-09-22 09:04 UTCGHSA enrichment
  23. 2026-09-22 04:46 UTCGHSA enrichment
  24. 2026-09-22 00:29 UTCGHSA enrichment
  25. 2026-09-21 20:12 UTCGHSA enrichment
Show 75 more
  1. 2026-09-21 19:09 UTCCISA KEV update
  2. 2026-09-21 15:55 UTCGHSA enrichment
  3. 2026-09-21 11:38 UTCGHSA enrichment
  4. 2026-09-21 07:20 UTCGHSA enrichment
  5. 2026-09-21 03:02 UTCGHSA enrichment
  6. 2026-09-20 22:43 UTCEG score recompute
  7. 2026-09-20 22:43 UTCGHSA enrichment
  8. 2026-09-20 18:26 UTCGHSA enrichment
  9. 2026-09-20 14:09 UTCGHSA enrichment
  10. 2026-09-20 09:52 UTCGHSA enrichment
  11. 2026-09-20 05:35 UTCGHSA enrichment
  12. 2026-09-20 01:18 UTCGHSA enrichment
  13. 2026-09-19 21:01 UTCGHSA enrichment
  14. 2026-09-19 16:44 UTCGHSA enrichment
  15. 2026-09-19 12:27 UTCGHSA enrichment
  16. 2026-09-19 08:10 UTCGHSA enrichment
  17. 2026-09-19 03:53 UTCGHSA enrichment
  18. 2026-09-18 23:36 UTCGHSA enrichment
  19. 2026-09-18 19:20 UTCCISA KEV update
  20. 2026-09-18 19:17 UTCGHSA enrichment
  21. 2026-09-18 15:00 UTCGHSA enrichment
  22. 2026-09-18 14:15 UTCCISA KEV update
  23. 2026-09-18 10:43 UTCGHSA enrichment
  24. 2026-09-18 06:26 UTCGHSA enrichment
  25. 2026-09-18 02:09 UTCGHSA enrichment
  26. 2026-09-17 21:52 UTCGHSA enrichment
  27. 2026-09-17 17:34 UTCGHSA enrichment
  28. 2026-09-17 13:18 UTCGHSA enrichment
  29. 2026-09-17 09:01 UTCGHSA enrichment
  30. 2026-09-17 04:44 UTCGHSA enrichment
  31. 2026-09-17 00:27 UTCGHSA enrichment
  32. 2026-09-16 20:10 UTCGHSA enrichment
  33. 2026-09-16 15:53 UTCEG score recompute
  34. 2026-09-16 15:53 UTCGHSA enrichment
  35. 2026-09-16 14:10 UTCCISA KEV update
  36. 2026-09-16 14:05 UTCEPSS rescore
  37. 2026-09-16 14:04 UTCEPSS rescore
  38. 2026-09-16 11:35 UTCGHSA enrichment
  39. 2026-09-16 07:17 UTCGHSA enrichment
  40. 2026-09-16 03:00 UTCGHSA enrichment
  41. 2026-09-15 22:43 UTCGHSA enrichment
  42. 2026-09-15 18:26 UTCGHSA enrichment
  43. 2026-09-15 14:09 UTCGHSA enrichment
  44. 2026-09-15 09:52 UTCGHSA enrichment
  45. 2026-09-15 05:35 UTCGHSA enrichment
  46. 2026-09-15 01:18 UTCGHSA enrichment
  47. 2026-09-14 21:01 UTCGHSA enrichment
  48. 2026-09-14 19:24 UTCCISA KEV update
  49. 2026-09-14 16:39 UTCGHSA enrichment
  50. 2026-09-14 12:22 UTCGHSA enrichment
  51. 2026-09-14 08:05 UTCGHSA enrichment
  52. 2026-09-14 03:48 UTCGHSA enrichment
  53. 2026-09-13 23:31 UTCGHSA enrichment
  54. 2026-09-13 19:14 UTCGHSA enrichment
  55. 2026-09-13 14:57 UTCGHSA enrichment
  56. 2026-09-13 10:40 UTCGHSA enrichment
  57. 2026-09-13 06:23 UTCGHSA enrichment
  58. 2026-09-13 02:05 UTCGHSA enrichment
  59. 2026-09-12 21:49 UTCGHSA enrichment
  60. 2026-09-12 17:32 UTCGHSA enrichment
  61. 2026-09-12 13:14 UTCGHSA enrichment
  62. 2026-09-12 08:57 UTCGHSA enrichment
  63. 2026-09-12 04:40 UTCGHSA enrichment
  64. 2026-09-12 00:23 UTCGHSA enrichment
  65. 2026-09-11 20:06 UTCGHSA enrichment
  66. 2026-09-11 18:49 UTCCISA KEV update
  67. 2026-09-11 15:49 UTCGHSA enrichment
  68. 2026-09-11 11:31 UTCGHSA enrichment
  69. 2026-09-11 07:07 UTCGHSA enrichment
  70. 2026-09-11 02:50 UTCGHSA enrichment
  71. 2026-09-10 22:33 UTCGHSA enrichment
  72. 2026-09-10 19:28 UTCCISA KEV update
  73. 2026-09-10 18:16 UTCGHSA enrichment
  74. 2026-09-10 13:57 UTCGHSA enrichment
  75. 2026-09-10 09:40 UTCGHSA enrichment

Publicly available exploits

(1 reference)

Working exploit code is in the public domain. Defenders should treat patch urgency accordingly — public PoCs typically lead to mass-exploitation within 24-72 hours.

  • Nucleihttp/cves/2021/CVE-2021-20090.yaml
    First seen Jan 1, 2021

    Buffalo WSR-2533DHPL2 - Path Traversal

    Open source ↗

Related CVEs(same CWE)

Frequently asked(6)

What is CVE-2021-20090?
CVE-2021-20090 is a critical vulnerability published on April 29, 2021. A path traversal vulnerability in the web interfaces of Buffalo WSR-2533DHPL2 firmware version <= 1.02 and WSR-2533DHP3 firmware version <= 1.24 could allow unauthenticated remote attackers to bypass authentication.
When was CVE-2021-20090 disclosed?
CVE-2021-20090 was first published in the National Vulnerability Database on April 29, 2021, with the most recent update on November 3, 2025. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2021-20090 actively exploited?
Yes. CISA added CVE-2021-20090 to the Known Exploited Vulnerabilities catalog on November 3, 2021, affecting Arcadyan Buffalo Firmware. KEV listing indicates confirmed exploitation in the wild; this CVE warrants immediate patching attention.
What is the CVSS score of CVE-2021-20090?
CVE-2021-20090 has a CVSS v3 base score of 9.8 (NVD).
Which products are affected by CVE-2021-20090?
CVE-2021-20090 affects Arcadyan Buffalo Firmware. The full affected-products list, including version ranges and fixed versions, is shown in the Affected Packages section of this page.
How do I remediate CVE-2021-20090?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-20090, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

Explore the affected products and dependency analysis for CVE-2021-20090

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