CVE-2021-27137
HighExploitedPublic exploitAn unsafe strcpy in the UPnP handling functionality allows an unauthenticated remote attacker to send a request that would overflow an internal fixed buffer.
Published Jul 16, 2026 · Updated Jul 22, 2026 · Also known as EUVD-2021-34854, GHSA-qx3v-2jx6-8m2c
Key Facts
Patch immediately- CVE-2021-27137 is a high-severity vulnerability (CVSS 8.1 v3.1) affecting DD-WRT.
- It is exploited in the wild, listed in CISA KEV, Industry KEV feed, CIRCL KEV, ENISA EUVD since Jun 3, 2026. Public exploit code is available.
- EPSS estimates a 4.0% probability of exploitation in the next 30 days.
- Fixed versions are available, including DD-WRT 45724.
- Brandefense priority: patch immediately, because it is listed as exploited in the wild.
CVSS v3.1
8.1
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
EPSS (30-day exploit likelihood)
4.0%
Higher than 90.3% of all scored CVEs
Exploited in the wild
Yes
4 catalog listings
Public exploit code
Available
Proof-of-concept or weaponized module
Get the full CVE-2021-27137 brief as a PDF
Every affected product and fixed release, exploitation status and a first 24 hours response checklist, emailed within minutes.
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).
Known-Exploited Catalog Listings
| Catalog | Added | Remediation due | Ransomware use |
|---|---|---|---|
| CISA KEV | Jul 21, 2026 | Jul 24, 2026 | Not reported |
| Industry KEV feed | Jun 3, 2026 | Jul 24, 2026 | Not reported |
| CIRCL KEV | Jul 21, 2026 | Jul 24, 2026 | Not reported |
| ENISA EUVD | Jul 21, 2026 | n/a | Not reported |
Required action: Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines.
Affected Products
3 affected entries in total| Product | Affected versions | Fixed in |
|---|---|---|
| DD-WRTDd-Wrt | See advisory | 45724 |
Patched Releases
DD-WRT
45724
Timeline
Added to Industry KEV feed
Jun 3, 2026
Publicly disclosed
Jul 16, 2026
Added to CISA KEV
Jul 21, 2026
Added to CIRCL KEV
Jul 21, 2026
Added to ENISA EUVD
Jul 21, 2026
Last updated
Jul 22, 2026
Weakness Type
- CWE-121 Stack-based Buffer Overflow
References
- exploitVulnCheck exploitation report
- exploitVulnCheck exploitation report
- exploitVulnCheck exploitation report
- exploitVulnCheck exploitation report
- otherhttps://securityaffairs.com/193290/uncategorized/iot-botnet-c0xmo-adds-competitor-killing-capability.html
FAQ
Common Questions.
An issue was discovered in router/upnp/src/ssdp.c in DD-WRT before 45724.
Affected: DD-WRT. The full list is in the CVE brief.
It is exploited in the wild, listed in CISA KEV, Industry KEV feed, CIRCL KEV, ENISA EUVD since Jun 3, 2026.
Yes. It was added on Jul 21, 2026 with a federal remediation due date of Jul 24, 2026.
Public exploit code is available.
Fixed versions are available, including DD-WRT 45724.
Brandefense priority: patch immediately, because it is listed as exploited in the wild.
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