CVE-2021-27137

CRITICALPre-NVD 8.19.0▲
EchelonGraph scoreHIGH confidence

Score elevated to 9.0 because this CVE is listed on the CISA Known Exploited Vulnerabilities catalog (added 2026-07-21), indicating real-world exploitation has been confirmed by US federal agencies. a secondary CVSS source baseline 8.1 retained for reference (NVD's own analysis pending). Confidence: HIGH.

Triggered by: CISA KEV (actively exploited)
Sources: cisa_kev, epss, ghsa, secondary
Trending — 4 sources updated this weekExploited in the wild
9.0EG
EchelonGraph verdictPatch nowTreat as an emergency — this is being exploited.
  • Actively exploited in the wild (CISA-KEV)
CISA-KEV: ExploitedEPSS PROB: 4%CVSS: 8.1Exploit: cisa kev · ssvc activeExposed: 0

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

An issue was discovered in router/upnp/src/ssdp.c in DD-WRT before 45724. An unsafe strcpy in the UPnP handling functionality allows an unauthenticated remote attacker to send a request that would overflow an internal fixed buffer. Exploitation requires the DD-WRT user to enable UPnP (which is off by default, and only listens on internal interfaces by default). This occurs in ssdp_msearch (reachable by an M-SEARCH request).

CVSS v3
8.1
EG Score
9.0(high)
EG Risk
81(Attend)
EG Risk 81/100SSVC: Attend

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
Severity90% × 45%
Exploitation100% × 40%
Automatability0% × 15%
Action: Remediate soon — notable exploitation risk.
EPSS PROB
4%
EPSS %ILE
90%
KEV
⚠ Exploited

Published

July 16, 2026

Last Modified

July 22, 2026

Advisory Details (5)

Auto-updated Jul 16, 2026
⚠️ Active exploitation confirmed. No patch confirmed yet.
generic🟡 PoC Available

SSD Advisory – DD-WRT UPNP Buffer Overflow - SSD Secure Disclosure

https://ssd-disclosure.com/ssd-advisory-dd-wrt-upnp-buffer-overflow/
generic🔴 Active Exploitation

Inside the Cross-Platform Propagation of a New Gafgyt Variant C0XMO | FortiGuard Labs

https://www.fortinet.com/blog/threat-research/inside-cross-platform-propagation-of-new-gafgyt-variant-c0xmo
generic

C0XMO botnet spreads via DD-WRT router flaw, kills rival malware

https://www.bleepingcomputer.com/news/security/c0xmo-botnet-spreads-via-dd-wrt-router-flaw-kills-rival-malware/
generic

Changeset 45724 – DD-WRT

https://svn.dd-wrt.com/changeset/45724
generic

IoT Botnet C0XMO Adds Competitor-Killing Capability

https://securityaffairs.com/193290/uncategorized/iot-botnet-c0xmo-adds-competitor-killing-capability.html

Vendor Advisories for CVE-2021-27137(1)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Weakness Classification(1)

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

Data Freshness Timeline

(refreshed 57× in last 7d / 248× 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 509 total refreshes for this CVE.

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

Frequently asked(6)

What is CVE-2021-27137?
CVE-2021-27137 is a critical vulnerability published on July 16, 2026. An issue was discovered in router/upnp/src/ssdp.c in DD-WRT before 45724. An unsafe strcpy in the UPnP handling functionality allows an unauthenticated remote attacker to send a request that would overflow an internal fixed buffer. Exploitation requires the DD-WRT user to enable UPnP (which is off…
When was CVE-2021-27137 disclosed?
CVE-2021-27137 was first published in the National Vulnerability Database on July 16, 2026, with the most recent update on July 22, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2021-27137 actively exploited?
Yes. CISA added CVE-2021-27137 to the Known Exploited Vulnerabilities catalog on July 21, 2026, affecting DD-WRT DD-WRT. KEV listing indicates confirmed exploitation in the wild; this CVE warrants immediate patching attention.
What is the CVSS score of CVE-2021-27137?
CVE-2021-27137 has a CVSS v3 base score of 8.1 (NVD). EchelonGraph synthesises NVD + CISA KEV + FIRST EPSS + GHSA into a combined EG score of 9.0.
Which products are affected by CVE-2021-27137?
CVE-2021-27137 affects DD-WRT DD-WRT. 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-2021-27137?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-27137, 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-2021-27137

Explore →

Is Your Infrastructure Affected by CVE-2021-27137?

EchelonGraph automatically scans your cloud infrastructure and maps CVE exposure using blast radius analysis.

Start Free Scan →Browse All CVEs