Is CVE-2021-27137 actively exploited?

Yes. KEV Intelligence tracks CVE-2021-27137 as a known exploited vulnerability. Confidence is confirmed.

What exploitation activity has KEV Intelligence observed?

KEV Intelligence has not yet recorded sensor-observed exploitation attempts for CVE-2021-27137. Our sensors continue to monitor for activity targeting this CVE.

Which versions are affected?

CVE-2021-27137 affects DD-WRT DD-WRT. Reported affected version: 0 to < 45724.

Yes. CVE-2021-27137 is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog. KEV Intelligence attested it 3 hours ahead of CISA.

Vulnerability report

Exploited in the wild Confirmed confidence In CISA KEV

CVE-2021-27137

Q: How should organizations remediate it?

Prioritize remediation. Validate affected assets and apply vendor fixes on an accelerated timeline.

Q: Is it in CISA KEV?

Yes. CVE-2021-27137 is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog. KEV Intelligence attested it 3 hours ahead of CISA.

DD-WRT

DD-WRT / DD-WRT · affected before 45724

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Severity: CVSS 8.1 · High
Confidence: Confirmed
Exploit status: Exploited in the wild
EPSS: 16.5%
First observed: —
Last observed: —

Decision summary

What security teams need to know first

Direct answers before the deeper technical record.

What it is

CVE-2021-27137 is an unauthenticated vulnerability affecting DD-WRT DD-WRT. 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...

Is it exploited?

Yes. KEV Intelligence tracks this CVE as a known exploited vulnerability. Confidence is confirmed.

Who is affected?

DD-WRT / DD-WRT affected before 45724.

What should we do?

Prioritize remediation. Validate affected assets and apply vendor fixes on an accelerated timeline.

Overview

An issue was discovered in router/upnp/src/ssdp.c in DD-WRT before 45724

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).

Vendor Product Affected Status

DD-WRT DD-WRT Before 45724 Affected

Published: 16 Jul 2026
Exploitation Reported: 21 Jul 2026
Attack vector: Remote
Complexity: High
Privileges: None
User interaction: None

CVE References

CVE Record CVE.org · CVE Record https://www.cve.org/CVERecord?id=CVE-2021-27137
svn.dd-wrt.com/changeset/45724 svn.dd-wrt.com · CVE Record https://svn.dd-wrt.com/changeset/45724
ssd-disclosure.com/ssd-advisory-dd-wrt-upnp-buffer-overflow ssd-disclosure.com · CVE Record https://ssd-disclosure.com/ssd-advisory-dd-wrt-upnp-buffer-overflow/
securityaffairs.com/193290/uncategorized/iot-botnet-c0xmo-adds-c... securityaffairs.com · CVE Record https://securityaffairs.com/193290/uncategorized/iot-botnet-c0xmo-add...
bleepingcomputer.com/news/security/c0xmo-botnet-spreads-via-dd-wr... bleepingcomputer.com · CVE Record https://www.bleepingcomputer.com/news/security/c0xmo-botnet-spreads-v...
fortinet.com/blog/threat-research/inside-cross-platform-p... fortinet.com · CVE Record https://www.fortinet.com/blog/threat-research/inside-cross-platform-p...

Exploitation evidence

Why KEV Intelligence marks this CVE as exploited

Third-party attestation and first-party sensor observation are shown separately so teams can judge the evidence chain.

Exploited in the wild

CISA

Recorded 21 Jul 2026

Independent exploitation attestation added to the KEV Intelligence record.

Known exploited vulnerability sources

Per-source evidence links for KEV attestations are available through the KEV Intelligence Pro API.

Learn about Pro API access

Source	Added
All CISA Advisories First	2026-07-21 12:00 UTC
CISA	2026-07-21 14:32 UTC
CVE	2026-07-21 16:01 UTC

Detection

Operational artifacts and observed signals

Make the evidence actionable in scanner, SOC, and edge-control workflows.

Observed signals

Request targets: 0
User-Agents: 0

Raw values available in Pro and Enterprise.

Scanner coverage

No scanner integrations recorded yet.

Virtual patch status

No KEV Intelligence virtual patch is currently available. Future rules ship for ModSecurity, Cloudflare, and AWS WAF.

Learn about virtual patches →

No detection artifacts or sensor request patterns are available for this CVE yet.

Check back as sensor telemetry and scanner integrations are updated.

Risk and context

Severity, weaknesses, and research context

CVSS v3.1

8.1 High

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

EPSS

16.5%

Weaknesses

Stack-based Buffer Overflow CWE-121

Recent mention · All CISA Advisories

CISA Adds Four Known Exploited Vulnerabilities to Catalog

CISA has added four new vulnerabilities to its Known Exploited Vulnerabilities (KEV) Catalog, based on evidence of active exploitation. CVE-2021-27137 DD-WRT Stack-Based Buffer Overflow Vulnerability CVE-2026-0770 Langflow Inclusion of Functionality from Untrusted Control...

Read full advisory

Timeline

From disclosure to observed exploitation

21 Jul 2026
KEV confirmed by CVE

Exploitation attested by an external source
21 Jul 2026
Added to CISA KEV

Listed in the CISA Known Exploited Vulnerabilities catalog
21 Jul 2026
Added to KEV Intelligence KEV Feed

High-confidence, third-party attested exploitation
16 Jul 2026
CVE published

Vulnerability disclosed publicly
10 Feb 2021
CVE ID reserved

Identifier reserved by the CNA

Pro API

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Evidence confidence and provenance
First-party sensor telemetry
PoC and scanner references
Affected versions and enrichment
Automation-ready JSON delivery

GET /api/v2/pro/kevs/CVE-2021-27137

Free JSON includes basic KEV fields

{
  "cve_id": "CVE-2021-27137",
  "confidence": "Confirmed",
  "cvss_score": 8.1,
  "cvss_estimated": false,
  "epss_score": 0.16488,
  "exploit_status": {
    "exploited_in_the_wild": true,
    "active_exploitation_observed": false
  },
  "sensor_telemetry": { "attempts": 0, "sensors": 0 }
}

Early warning alerts

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