CVE-2021-27239

HIGHNVD 8.88.8—
EchelonGraph scoreMEDIUM confidence

This high-severity CVE scores 8.8 under NVD CVSS v3. EPSS exploit probability: 0.7%, top 49% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).

Triggered by: NVD CVSS baseline
Sources: epss, nvd
8.8
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS: 1%CVSS: 8.8Exploit: NoneExposed: 0

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

This vulnerability allows network-adjacent attackers to execute arbitrary code on affected installations of NETGEAR R6400 and R6700 firmware version 1.0.4.98 routers. Authentication is not required to exploit this vulnerability. The specific flaw exists within the upnpd service, which listens on UDP port 1900 by default. A crafted MX header field in an SSDP message can trigger an overflow of a fixed-length stack-based buffer. An attacker can leverage this vulnerability to execute code in the context of root. Was ZDI-CAN-11851.

CVSS v3
8.8
EG Score
8.8(medium)
EG Risk
44(Track)
EG Risk 44/100SSVC: Track

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
Severity88% × 45%
Exploitation1% × 40%
Automatability30% × 15%
Action: Routine — remediate on your standard cadence.
EPSS
51.0%
KEV
Not listed

Published

March 29, 2021

Last Modified

November 21, 2024

References (4)

Weakness Classification(1)

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

Data Freshness Timeline

(refreshed 13× in last 7d / 48× 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.

  1. 2026-07-23 14:16 UTCEPSS rescore
  2. 2026-07-23 01:59 UTCEG score recompute
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  72. 2026-05-26 19:04 UTCGHSA enrichment
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Frequently asked(5)

What is CVE-2021-27239?
CVE-2021-27239 is a high vulnerability published on March 29, 2021. This vulnerability allows network-adjacent attackers to execute arbitrary code on affected installations of NETGEAR R6400 and R6700 firmware version 1.0.4.98 routers. Authentication is not required to exploit this vulnerability. The specific flaw exists within the upnpd service, which listens on…
When was CVE-2021-27239 disclosed?
CVE-2021-27239 was first published in the National Vulnerability Database on March 29, 2021, with the most recent update on November 21, 2024. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2021-27239 actively exploited?
CVE-2021-27239 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 51.0% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2021-27239?
CVE-2021-27239 has a CVSS v3 base score of 8.8 (NVD).
How do I remediate CVE-2021-27239?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-27239, 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.

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