DD-WRT Stack-Based Buffer Overflow Vulnerability (CVE-2021-27137)
Severity: high · Patch status: patched · Since 2026-07-21 · CVE-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 added CVE-2021-27137 to its Known Exploited Vulnerabilities catalog on Jul 21, 2026, which means attackers are exploiting it in the wild.
What to do
- 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.
- US federal agencies must remediate by Jul 24, 2026 (BOD 22-01); treat that as the outer limit.
Sources
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