Vulnerability report

Exploited in the wild Confirmed confidence In CISA KEV

CVE-2021-27137

DD-WRT

DD-WRT · affected before 45724

Watch CVE-2021-27137 Browse KEV feed
Severity
CVSS 8.1 · High
Confidence
Confirmed
Exploit status
Exploited in the wild
EPSS
4.0%
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. 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. Previdian tracks this CVE as a known exploited vulnerability. Confidence is confirmed. Listed in CISA KEV. Also confirmed by third-party sources.

Who is affected?

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).

DD-WRT Affected
DD-WRT
Before 45724
Published
16 Jul 2026
Exploitation Reported
21 Jul 2026
Attack vector
Remote
Complexity
High
Privileges
None
User interaction
None

Tags

edge cisa

CVE References

Exploitation evidence

Why Previdian 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

A trusted third party reported exploitation.

Known exploited vulnerability sources

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

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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
User-Agents
Callback hosts
0
0
0

Request targets and User-Agents available in Pro. Callback host details available in Enterprise.

Scanner coverage

No scanner integrations recorded yet.

Virtual patch status

No Previdian 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

Potential damage if exploited. Separate from whether attackers are using it.

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

EPSS

4.0%

Estimated chance of exploitation in the next 30 days. Previdian's warning comes from evidence, not this score.

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

  1. 16:01 UTC

    KEV confirmed by CVE

    Exploitation attested by an external source

  2. 14:32 UTC

    Added to CISA KEV

    Listed in the CISA Known Exploited Vulnerabilities catalog

  3. 12:00 UTC

    Added to Previdian KEV Feed

    High-confidence, third-party attested exploitation

  4. 00:00 UTC

    CVE published

    Vulnerability disclosed publicly

  5. 00:00 UTC

    CVE ID reserved

    Identifier reserved by the CNA

Pro API

Automate this intelligence

Confidence, exploit status, sensor telemetry, PoCs, scanner integrations, mentions, and tags are available programmatically for VM, SOC, and CTI workflows.

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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

Sample API response 
{
  "cve_id": "CVE-2021-27137",
  "confidence": "Confirmed",
  "cvss_score": 8.1,
  "cvss_estimated": false,
  "epss_score": 0.03995,
  "exploit_status": {
    "exploited_in_the_wild": true,
    "active_exploitation_observed": false
  },
  "sensor_telemetry": { "attempts": 0, "sensors": 0 }
}