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Exploitation reportedNot in CISA KEV yet

CVE-2021-39509

Exploitation reported by one source. First attested on 2024-10-09 by GCVE · shadowserver.

  • Published2021-08-24
  • WeaknessCWE-77

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

Description

An issue was discovered in D-Link DIR-816 DIR-816A2_FWv1.10CNB05_R1B011D88210 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.

Timeline

dates in UTC
  1. 2021-08-2419:15CVE publishedNVD
  2. 2024-10-0903:25Listed as exploited by GCVEGCVE
  3. 2024-10-0903:25Exploitation first reportedGCVE

Observed activity

isMalicious corpus · updated 2026-11-04 09:37 UTC
Indicators tagged with this CVE, per day0 indicators over 7 days
Block these indicators
  • Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2021-39509?format=txt
  • CSV export: https://api.ismalicious.com/edl/cve/CVE-2021-39509?format=csv
  • TAXII collection of exploited CVEs
  • The EDL and CSV take an API key on the Pro plan.

Versions per branch

NVD
Dlink dir-816 firmwareversion to verify
BranchAffectedFixed in
1.10= 1.10cnb05_r1b011d88210no fix published

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Fix

Advisories and patches

Detection

Nuclei template
none so far
ProjectDiscovery
Exploit-DB
no entry
Exploit-DB
Proof-of-concept repositories
none listed
PoC-in-GitHub
Metasploit modules
none listed
Metasploit Framework

Sources

  • GCVEexploitation2024-10-09
  • NVDCVSS 3.19.8read 2026-10-23
  • NVDCVSS 2.07.5read 2026-10-23
  • NVDweakness (CWE)CWE-77read 2026-10-23
  • FIRST EPSSEPSS score5.1 %2026-11-03

Identifiers

Technical details

CVSS v3 Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Published
2021-08-24
Last Modified
2026-06-17
NVD status
Modified

Frequently asked questions

What is CVE-2021-39509?

An issue was discovered in D-Link DIR-816 DIR-816A2_FWv1.10CNB05_R1B011D88210 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.

Is CVE-2021-39509 actively exploited?

Active exploitation of CVE-2021-39509 has not been confirmed. Its EPSS score was 5.1% on 2026-11-03, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2021-39509?

CVE-2021-39509 has a CVSS v3 base score of 9.8 (CRITICAL severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

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