Cyber Resilience

CVE-2021-40655

Access Control in Dlink Dir-605L Firmware 2.01mt

CISA KEVActive ExploitationEUVD ExploitedPublic PoCAccess Control
Published
24 September 2021
Modified
10 November 2025
KEV Added
16 May 2024
Patch / advisory
View advisory
CVSS Score v3.1 7.5
Click a component to see what it means
Raw vectorCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
EPSS Score 0.87 99.7th percentile
Risk Priority 84 floored blend · peak EPSS

Summary

CVE-2021-40655 is a high-severity Incorrect Authorization (CWE-863) vulnerability in Dlink Dir-605L Firmware. Its CVSS base score is 7.5 (High).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploitation for Privilege Escalation (T1068); ranked in the top 0.3% of CVEs by exploit likelihood; CISA has added it to the Known Exploited Vulnerabilities catalog; a public proof-of-concept is referenced.

Deeper analysis AI-assisted summary

Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.

CVE-2021-40655 is an information disclosure vulnerability affecting the D-Link DIR-605 B2 router running firmware version 2.01MT. The flaw resides in the /getcfg.php endpoint and stems from incorrect authorization (CWE-863), which fails to enforce proper access controls on configuration data.

An unauthenticated remote attacker can exploit the issue by sending a crafted POST request to the affected endpoint. Successful exploitation yields the device's administrative username and password, exposing sensitive credentials without requiring any user interaction or prior authentication.

The vulnerability is tracked in CISA's Known Exploited Vulnerabilities catalog, confirming observed in-the-wild exploitation. D-Link has published security bulletins addressing affected hardware, and public proof-of-concept material is available in repositories that demonstrate the request forgery technique.

OWASP Top 10 for Web (2025)

A01:2025 Broken Access Control

EU & UK References

Vulnerability Data

An informtion disclosure issue exists in D-LINK-DIR-605 B2 Firmware Version : 2.01MT. An attacker can obtain a user name and password by forging a post request to the / getcfg.php page

CWE(s)
CWE-863
KEV Date Added
16 May 2024

Related Threats

MITRE ATT&CK Enterprise Techniques

T1068 Exploitation for Privilege Escalation Privilege Escalation
Adversaries may exploit software vulnerabilities in an attempt to elevate privileges.
attack.mitre.org →
T1548 Abuse Elevation Control Mechanism Privilege Escalation
Adversaries may circumvent mechanisms designed to control privilege elevation to gain higher-level permissions.
attack.mitre.org →
T1548.002 Bypass User Account Control Privilege Escalation
Adversaries may bypass UAC mechanisms to elevate process privileges on system.
attack.mitre.org →
T1548.003 Sudo and Sudo Caching Privilege Escalation
Adversaries may perform sudo caching and/or use the sudoers file to elevate privileges.
attack.mitre.org →
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.
attack.mitre.org →
T1210 Exploitation of Remote Services Lateral Movement
Adversaries may exploit remote services to gain unauthorized access to internal systems once inside of a network.
attack.mitre.org →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2024-9559Same product: Dlink Dir-605L
CVE-2024-9532Same product: Dlink Dir-605L
CVE-2024-9549Same product: Dlink Dir-605L
CVE-2024-9565Same product: Dlink Dir-605L
CVE-2024-9555Same product: Dlink Dir-605L
CVE-2024-9557Same product: Dlink Dir-605L
CVE-2024-9562Same product: Dlink Dir-605L
CVE-2024-9550Same product: Dlink Dir-605L
CVE-2024-9553Same product: Dlink Dir-605L
CVE-2024-9552Same product: Dlink Dir-605L

Affected Assets

dlink
dir-605l firmware
2.01mt

Mitigating Controls

Control response

Prevent
Stop it (NIST 800-53)

—

Detect
Catch it (NIST detect / respond)

—

Harden
Shrink the surface (DISA STIG)
  • 5 hardening rules · 3 OS baselines
Validate
Prove the fix (OWASP ASVS)

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Likely Mitigating Controls AI

Per-CVE control mapping for this CVE has not run yet; the list below is derived from the weakness types (CWEs) cited in the NVD entry.

AC-1 Policy and Procedures
addresses: CWE-863

Periodic review and update of procedures reduces incorrect authorization implementations over time.

AC-13 Supervision and Review — Access Control
addresses: CWE-863

Supervision identifies cases where authorization logic incorrectly permits unauthorized actions.

AC-16 Security and Privacy Attributes
addresses: CWE-863

Defining permitted attribute values and auditing modifications reduces the chance of incorrect authorization outcomes due to tampered or missing labels.

AC-17 Remote Access
addresses: CWE-863

The authorization process and usage restrictions help prevent incorrect authorization for remote access types.

AC-18 Wireless Access
addresses: CWE-863

Establishing configuration and connection requirements helps ensure correct rather than incorrect authorization for wireless access.

AC-19 Access Control for Mobile Devices
addresses: CWE-863

Establishing connection authorization processes for mobile devices helps ensure authorization decisions are correctly implemented rather than incorrect.

AC-2 Account Management
addresses: CWE-863

Monitoring account use, notifying on changes, and reviewing accounts for compliance corrects incorrect authorization assignments.

AC-20 Use of External Systems
addresses: CWE-863

Ensures authorization decisions for external system use are correctly implemented and enforced.

Mitigating Controls (NIST CSF 2.0) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.

PR.AA-05 mostly match
prevents

Defining, enforcing, and reviewing access authorizations and least privilege directly prevents incorrect authorization checks.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

A.5.15 Access control partial match
prevents

Requiring consistency between access rights and classification plus formal approval steps ensures that the authorization logic correctly distinguishes between entities that should and should not be granted access.

A.5.18 Access rights partial match
prevents

Enforcing policy-driven approval and role-change reviews stops incorrect or stale authorization decisions from remaining in effect after job changes or terminations.

A.8.3 Information access restriction partial match
prevents

By tying access rights to identity, device, location and classification, the control reduces the likelihood that an authorization decision will be based on an incorrect or bypassed policy.

Hardening callouts derived

Configuration rules from DISA STIG baselines that bear on weaknesses of the type cited by this CVE. Each rule is shown with the relationship its mapping actually records, against the CWE it was authored against. Derived via CVE→CWE over `controls_xwalks` (authoritative rows only; rows rated `none` are excluded).

Oracle Linux 8 (2 rules)
  • V-248581 OL 8 must require users to provide a password for privilege escalation. prevents CWE-863
  • V-252656 The OL 8 operating system must not be configured to bypass password requirements for privilege escalation. prevents CWE-863
RHEL 7 (1 rule)
  • V-204430 The Red Hat Enterprise Linux operating system must be configured so that users must re-authenticate for privilege escalation. prevents CWE-863
RHEL 8 (1 rule)
  • V-251712 The RHEL 8 operating system must not be configured to bypass password requirements for privilege escalation. prevents CWE-863

References