CVE intelligence and bounded remediation

CVE-2021-39510 — Dlink Dir-816 Firmware security vulnerability

Critical CVSS 9.8

An issue was discovered in D-Link DIR816_A1_FW101CNB04 750m11ac wireless router, The HTTP request parameter is used in the handler function of /goform/form2userconfig.cgi route, which can construct the user name string to delete the user function. This can lead to command injection through shell metacharacters.

Severity
Critical
CVSS
9.8 (3.1)
Published
2021-08-24
CISA KEV
Not currently listed
Ecosystem
operating-system
Weaknesses
CWE-77

Affected products

  • dlink / dir-816_firmware / 101cnb04

Matched remediation archetype

Command, code, expression, and template injection

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Check exposure

  • Trace untrusted values to process execution, interpreters, evaluators, template engines, dynamic imports, and administrative scripting features.
  • Determine whether the affected path is reachable across each trust boundary and which service account or host privilege it inherits.
  • Review configuration for optional execution features, unsafe compatibility modes, and shell invocation.

Remediate safely

  • Replace string-built commands or evaluated code with fixed operations and structured argument APIs that do not invoke a shell.
  • Use strict allowlists for operation identifiers and reject unexpected input before it reaches any interpreter.
  • Update the affected component and add inert regression tests covering metacharacters, encoding variants, and alternate request paths.

Authoritative sources

Complete CVE record and remediation plan

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