CVE-2021-27173Public exploitNetwork attack vector

Unauthenticated Telnet exposure via MAC-derived backdoor

Published Feb 10, 2021 · Updated Aug 3, 2024

Improper authentication in FiberHome HG6245D firmware through RP2613 allows remote attackers to expose the Telnet CLI via HTTPS. The HTTP server's /telnet handler accepts an enable flag and a key derived from the BR0 interface MAC address, then changes firewall rules without authenticating the request. Access requires network reachability to the HTTPS management service and derivation of the BR0 MAC; the endpoint exposes port 23 but does not itself bypass Telnet login.

CVSS severity7.5
High
EPSS probability12.67%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper authentication in FiberHome HG6245D firmware through RP2613 allows remote attackers to expose the Telnet CLI via HTTPS. The HTTP server's /telnet handler accepts an enable flag and a key derived from the BR0 interface MAC address, then changes firewall rules without authenticating the request. Access requires network reachability to the HTTPS management service and derivation of the BR0 MAC; the endpoint exposes port 23 but does not itself bypass Telnet login.

The record

CVE
CVE-2021-27173
Published
Feb 10, 2021
Updated
Aug 3, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-287, T1562.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Feb 10, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 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

7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
5.0NIST NVDAV:N/AC:L/Au:N/C:N/I:P/A:N

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-287Improper Authentication
T1562.004Disable or Modify System Firewall

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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