CVE-2021-27137An issue was discovered in router/upnp/src/ssdp.c in DD-WRT before 45724.
Updated under an hour ago ()
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It affects DD-WRT and 1 other product. Add what you run to find out whether that includes you.
CISA lists it as known exploited since Jul 21, 2026; federal agencies had to remediate by Jul 24, 2026. Treat that date as your deadline.
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Free account, 1 product
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).
- CVSS
- 8.1 HIGH (v3.1, CNA)CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
- Weakness (CWE)
- CWE-121
- Known exploited
- Added to CISA KEV Jul 21, 2026; federal remediation due Jul 24, 2026Apply 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.
- EPSS (exploitation in the next 30 days)
- 4.00% (percentile 90)
- Assigned by
- mitre
- NVD analysis
- Analyzed
- Record last updated
- Jul 22, 2026
- First seen by InfoSec Signals
- Oct 9, 2026
Affected products
DD-WRT DD-WRT dd_wrt:dd_wrt (from the name) | before 45724 | CNA record |
dd-wrt dd-wrt dd-wrt:dd-wrt | before 45724 | NVD |
References
- https://svn.dd-wrt.com/changeset/45724patch
- https://ssd-disclosure.com/ssd-advisory-dd-wrt-upnp-buffer-overflow/exploit, third-party-advisory
- https://securityaffairs.com/193290/uncategorized/iot-botnet-c0xmo-adds-competitor-killing-capability.htmlexploit, third-party-advisory
- https://www.bleepingcomputer.com/news/security/c0xmo-botnet-spreads-via-dd-wrt-router-flaw-kills-rival-malware/exploit, third-party-advisory
- https://www.fortinet.com/blog/threat-research/inside-cross-platform-propagation-of-new-gafgyt-variant-c0xmoexploit
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-27137us-government-resource
The CVE record on cve.org NVD's entry
The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.