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CVE-2021-27137.

Severity, exploit probability and exploitation status for one vulnerability, drawn from NVD, FIRST EPSS and CISA's exploited catalogue.

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known exploited DD-WRT Stack-Based Buffer Overflow Vulnerability

Vendor / product: DD-WRT - DD-WRT
Listed by CISA: 2026-07-21
Federal fix deadline: 2026-07-24 (passed)
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.

Scores

CVSS 3.1: 8.1 high CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
EPSS: 16.5% estimated probability of exploitation in the next 30 days (higher than 97% of all CVEs)
Weakness class: CWE-121

ATT&CK techniques

inferred from weakness class no curated mapping exists for this CVE; these are the techniques typically seen with CWE-121 vulnerabilities

ReconnaissanceResource DevelopmentInitial Access ExecutionPersistencePrivilege Escalation StealthDefense ImpairmentCredential AccessDiscoveryLateral MovementCollectionCommand and ControlExfiltrationImpact

T1190 Exploit Public-Facing Application

Initial Access

Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network.

Inferred from CWE-121.

T1190 on attack.mitre.org

T1059 Command and Scripting Interpreter

Execution

Adversaries may abuse command and script interpreters to execute commands, scripts, or binaries.

Inferred from CWE-121.

T1059 on attack.mitre.org

T1203 Exploitation for Client Execution

Execution

Adversaries may exploit software vulnerabilities in client applications to execute code.

Inferred from CWE-121.

T1203 on attack.mitre.org

T1204 User Execution

Execution

An adversary may rely upon specific actions by a user in order to gain execution.

via sub-technique T1204.002 Malicious File

Inferred from CWE-121.

T1204 on attack.mitre.org

T1574 Hijack Execution Flow

ExecutionStealth

Adversaries may execute their own malicious payloads by hijacking the way operating systems run programs.

Inferred from CWE-121.

T1574 on attack.mitre.org

T1068 Exploitation for Privilege Escalation

Privilege Escalation

Adversaries may exploit software vulnerabilities in an attempt to elevate privileges.

Inferred from CWE-121.

T1068 on attack.mitre.org

See these techniques on the full ATT&CK matrix.

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).

Published: 2026-07-16
Last modified: 2026-07-22
NVD status: Analyzed

References

CVSS measures how bad exploitation would be; EPSS estimates how likely exploitation is within 30 days; the CISA listing means it is already happening. Read them together: a CVSS 9.8 with EPSS 0.04% is usually less urgent than a CVSS 7.2 on the exploited list. Data: NVD, FIRST EPSS, CISA KEV; detail is cached for a week, scores for a day. ATT&CK techniques come from the CTID KEV mappings project where a curated mapping exists, otherwise they are inferred from the weakness class and labelled as such. ATT&CK is a registered trademark of The MITRE Corporation. © 2026 The MITRE Corporation. This work is reproduced and distributed with the permission of The MITRE Corporation.