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 — 4 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 Jul 28, 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 30× in last 7d / 169× 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 354 total refreshes for this CVE.

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