CVE-2021-35327Public exploitNetwork attack vector

Unauthenticated shell access via Telnet enablement

Published Aug 5, 2021 · Updated Aug 4, 2024

Missing authorization in TOTOLINK A720R firmware 4.1.5cu.470_B20200911 allows remote attackers to enable Telnet via a crafted POST request. The /cgi-bin/cstecgi.cgi endpoint accepts the setTelnetCfg topic with telnet_enabled set to 1 without checking authorization, starting the service. Unauthenticated network access to the management endpoint is sufficient; the published default root credentials then grant an administrative shell over Telnet.

CVSS severity9.8
Critical
EPSS probability1.38%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Missing authorization in TOTOLINK A720R firmware 4.1.5cu.470_B20200911 allows remote attackers to enable Telnet via a crafted POST request. The /cgi-bin/cstecgi.cgi endpoint accepts the setTelnetCfg topic with telnet_enabled set to 1 without checking authorization, starting the service. Unauthenticated network access to the management endpoint is sufficient; the published default root credentials then grant an administrative shell over Telnet.

The record

CVE
CVE-2021-35327
Published
Aug 5, 2021
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-862, T1078.001
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 5, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

9.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
7.5NIST NVDAV:N/AC:L/Au:N/C:P/I:P/A:P

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-862Missing Authorization
T1078.001Valid Accounts: Default Accounts

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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