DD-WRT - CraftedSignal Threat Feedhttps://feed.craftedsignal.io/products/dd-wrt/Trending threats, MITRE ATT&CK coverage, and detection metadata. Fed continuously.Hugoenhello@craftedsignal.iohello@craftedsignal.ioTue, 21 Jul 2026 15:00:30 +0000DD-WRT Stack-Based Buffer Overflow Vulnerability (CVE-2021-27137)https://feed.craftedsignal.io/briefs/2026-07-ddwrt-cve-2021-27137/Tue, 21 Jul 2026 15:00:30 +0000hello@craftedsignal.iohttps://feed.craftedsignal.io/briefs/2026-07-ddwrt-cve-2021-27137/CVE-2021-27137 is a stack-based buffer overflow vulnerability in DD-WRT's UPnP component that allows an unauthenticated attacker to trigger remote code execution on affected router devices.CVE-2021-27137 identifies a critical stack-based buffer overflow vulnerability within the UPnP service of DD-WRT firmware, potentially allowing unauthenticated remote code execution. This flaw enables attackers to overflow an internal buffer by sending specially crafted network packets, leading to the execution of arbitrary code on vulnerable DD-WRT devices. The vulnerability, first disclosed in 2021, has been added to CISA's Known Exploited Vulnerabilities Catalog, indicating active exploitation in the wild. Given DD-WRT's widespread use in consumer and small business networking equipment, successful exploitation can lead to full compromise of the router, potentially enabling network surveillance, traffic redirection, or further access to internal networks.

Attack Chain

  1. An unauthenticated attacker identifies a DD-WRT device with the vulnerable UPnP service exposed.
  2. The attacker crafts and sends specially malformed network packets to the UPnP service listening on the target DD-WRT device.
  3. The malformed packets are designed to exceed the bounds of an internal stack buffer within the UPnP service's processing routine.
  4. This crafted input triggers a stack-based buffer overflow condition in the UPnP service.
  5. The overflow corrupts memory, including critical return addresses on the stack.
  6. The attacker's injected shellcode, included in the crafted packets, gains control of the execution flow.
  7. The shellcode is executed in the context of the UPnP service, achieving unauthenticated remote code execution on the DD-WRT device.

Impact

Successful exploitation of CVE-2021-27137 grants unauthenticated remote code execution capabilities on vulnerable DD-WRT firmware devices. This allows an attacker to gain full control over the router, potentially leading to unauthorized access to the network, manipulation of network traffic, or establishment of persistent footholds. Given that DD-WRT is deployed in various environments, including homes and small businesses, the impact can range from personal data breaches to compromise of organizational networks. CISA's inclusion of this CVE in its KEV catalog indicates that this vulnerability has been actively exploited by threat actors, posing a significant and immediate risk to affected organizations and individuals.

Recommendation

  • Apply available vendor mitigations for CVE-2021-27137 as documented by DD-WRT and other vendors utilizing affected components.
  • If mitigations for CVE-2021-27137 are unavailable, discontinue use of the affected product immediately.
  • Ensure compliance with CISA’s BOD 26-04 guidance regarding prioritizing security updates based on risk, especially for internet-facing DD-WRT devices.
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