CVE-2021-27137

HIGHPre-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 — KEV-added this weekExploited in the wild
8.1
EchelonGraph verdictPatch nowTreat as an emergency — this is being exploited.
  • Actively exploited in the wild (CISA-KEV)
CISA-KEV: ExploitedEPSS: 11%CVSS: 8.1Exploit: NoneExposed: 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)
EPSS
95.4%
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 102× in last 7d / 102× 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 102 total refreshes for this CVE.

  1. 2026-07-22 14:06 UTCEPSS rescore
  2. 2026-07-22 14:06 UTCEPSS rescore
  3. 2026-07-22 13:40 UTCGHSA enrichment
  4. 2026-07-22 09:31 UTCGHSA enrichment
  5. 2026-07-22 05:22 UTCEG score recompute
  6. 2026-07-22 05:21 UTCGHSA enrichment
  7. 2026-07-22 05:20 UTCGHSA enrichment
  8. 2026-07-22 05:19 UTCGHSA enrichment
  9. 2026-07-22 05:18 UTCGHSA enrichment
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  24. 2026-07-22 05:03 UTCGHSA enrichment
  25. 2026-07-22 05:02 UTCGHSA enrichment
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  1. 2026-07-22 05:00 UTCGHSA enrichment
  2. 2026-07-22 04:59 UTCGHSA enrichment
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  4. 2026-07-22 04:57 UTCGHSA enrichment
  5. 2026-07-22 04:54 UTCGHSA enrichment
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  9. 2026-07-22 04:48 UTCGHSA enrichment
  10. 2026-07-22 04:46 UTCGHSA enrichment
  11. 2026-07-22 04:45 UTCGHSA enrichment
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  14. 2026-07-22 04:42 UTCGHSA enrichment
  15. 2026-07-22 04:40 UTCGHSA enrichment
  16. 2026-07-22 04:39 UTCGHSA enrichment
  17. 2026-07-22 00:29 UTCGHSA enrichment
  18. 2026-07-21 20:19 UTCEG score recompute
  19. 2026-07-21 20:19 UTCGHSA enrichment
  20. 2026-07-21 20:16 UTCGHSA enrichment
  21. 2026-07-21 20:16 UTCGHSA enrichment
  22. 2026-07-21 20:13 UTCGHSA enrichment
  23. 2026-07-21 20:11 UTCGHSA enrichment
  24. 2026-07-21 20:10 UTCGHSA enrichment
  25. 2026-07-21 20:09 UTCGHSA enrichment
  26. 2026-07-21 20:08 UTCGHSA enrichment
  27. 2026-07-21 20:08 UTCGHSA enrichment
  28. 2026-07-21 20:07 UTCGHSA enrichment
  29. 2026-07-21 20:05 UTCGHSA enrichment
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  47. 2026-07-21 19:36 UTCGHSA enrichment
  48. 2026-07-21 19:34 UTCGHSA enrichment
  49. 2026-07-21 19:31 UTCGHSA enrichment
  50. 2026-07-21 19:30 UTCGHSA enrichment
  51. 2026-07-21 19:29 UTCGHSA enrichment
  52. 2026-07-21 19:27 UTCGHSA enrichment
  53. 2026-07-21 19:25 UTCGHSA enrichment
  54. 2026-07-21 19:23 UTCGHSA enrichment
  55. 2026-07-21 19:21 UTCGHSA enrichment
  56. 2026-07-21 19:20 UTCGHSA enrichment
  57. 2026-07-21 19:20 UTCGHSA enrichment
  58. 2026-07-21 17:19 UTCEG score recompute
  59. 2026-07-21 17:19 UTCGHSA enrichment
  60. 2026-07-21 16:01 UTCEG score recompute
  61. 2026-07-21 16:01 UTCGHSA enrichment
  62. 2026-07-21 15:22 UTCEPSS rescore
  63. 2026-07-21 15:22 UTCEPSS rescore
  64. 2026-07-21 14:40 UTCEG score recompute▲ 0.90
  65. 2026-07-21 14:39 UTCGHSA enrichment
  66. 2026-07-21 14:37 UTCCISA KEV update
  67. 2026-07-20 17:05 UTCEPSS rescore
  68. 2026-07-19 14:28 UTCEPSS rescore
  69. 2026-07-19 02:36 UTCEG score recompute
  70. 2026-07-19 02:36 UTCGHSA enrichment
  71. 2026-07-19 02:27 UTCEPSS rescore
  72. 2026-07-19 02:27 UTCEPSS rescore
  73. 2026-07-18 10:02 UTCEPSS rescore
  74. 2026-07-18 10:02 UTCEPSS rescore
  75. 2026-07-17 06:23 UTCGHSA enrichment

Related CVEs(same CWE)

Frequently asked(6)

What is CVE-2021-27137?
CVE-2021-27137 is a high 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

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