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Findings

CVE-2021-27137

DD-WRT Stack-Based Buffer Overflow Vulnerability

Published Jul 16, 2026 · updated Jul 21, 2026 · 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 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).

Timeline

Detection, updates, and resolution for this record.

  1. Jul 16, 2026 · Catalog

    Detected

    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 (reachab

  2. Jul 21, 2026 · CISA KEV

    Known exploited

    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

  3. Jul 21, 2026 · Catalog

    Updated

    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 (reachab

  4. Jul 24, 2026 · CISA KEV

    Remediation due

    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

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.

CISA due date Jul 24, 2026

Affected

  • cpe dd-wrt/dd-wrtversion unspecified
  • vendor DD-WRT DD-WRTversion unspecified

Sources

  • CISA KEVCVE-2021-27137

    DD-WRT contains a stack-based buffer overflow vulnerability that could allow an unauthenticated attacker to overflow an internal buffer used by UPnP and trigger a code execution vulnerability.

    cisa.gov
  • CVE.orgCVE-2021-27137

    Official CVE identifier

    cve.org
  • FIRST EPSSCVE-2021-27137

    30-day exploitation probability 4.0%

    first.org
  • NIST NVDCVE-2021-27137

    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

    nvd.nist.gov

References

CVE-2021-27137 · ZeroDay Findings