CVE-2021-27137

Q: How do I fix CVE-2021-27137?

Upgrade dd-wrt to 45724 or later.

Q: Is CVE-2021-27137 being actively exploited?

Yes. CVE-2021-27137 is listed in the CISA Known Exploited Vulnerabilities catalog, which means exploitation has been observed in the wild. US federal agencies were required to remediate it by 2026-07-24. Treat it as a priority whatever its CVSS score says.

Q: How severe is CVE-2021-27137?

CVE-2021-27137 has a CVSS v3 base score of 8.1, rated high. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.

Q: What does CVE-2021-27137 affect?

Published advisories record a fix for dd-wrt (NVD). Only products with a sourced advisory are listed, so treat this as what we can cite rather than a complete inventory.

HIGHCISA KEVEPSS 97th pctl

8.1

CVSS v3

NVD

Description

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).

CWE-121Stack-based Buffer Overflow

How to fix

Remediation Available

dd-wrtNVD

Affected:< 45724Fixed in:45724CVE-2021-27137derived from NVD

TridentStack Control can deploy fixes like this automatically across your Windows, macOS, and Linux fleet. See how it works

Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.

CVSS v3 Vector

Exploitability

Attack VectorNetwork

Attack ComplexityHigh

Privileges RequiredNone

User InteractionNone

ScopeUnchanged

Impact

ConfidentialityHigh

IntegrityHigh

AvailabilityHigh

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

Exploit Intelligence

16.49%probability of exploitation in 30 days

97thpercentile

Very high risk: more likely to be exploited than 97% of all known CVEs.

Known Exploited Vulnerability (CISA KEV)

Remediation due: 2026-07-24

References

Patch1

svn.dd-wrt.com

Exploit4

Government Resource1

cisa.gov

Related Vulnerabilities

Other CWE-121 (Stack-based Buffer Overflow) vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2025-22457	Critical	9.0	100%	KEV + Ransom	Fix
CVE-2025-0282	Critical	9.0	100%	KEV + Ransom	-
CVE-2021-20038	Critical	9.8	100%	KEV + Ransom	-
CVE-2009-0927	High	8.8	97%	KEV	Fix
CVE-2020-10924	High	8.8	87%	-	-
CVE-2022-20705	Critical	10.0	80%	-	-

Common questions

How do I fix CVE-2021-27137?

Upgrade dd-wrt to 45724 or later.

Is CVE-2021-27137 being actively exploited?

Yes. CVE-2021-27137 is listed in the CISA Known Exploited Vulnerabilities catalog, which means exploitation has been observed in the wild. US federal agencies were required to remediate it by 2026-07-24. Treat it as a priority whatever its CVSS score says.

How severe is CVE-2021-27137?

CVE-2021-27137 has a CVSS v3 base score of 8.1, rated high. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.

What does CVE-2021-27137 affect?

Published advisories record a fix for dd-wrt (NVD). Only products with a sourced advisory are listed, so treat this as what we can cite rather than a complete inventory.

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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-07-22.