CVE-2021-27245Network attack vector

Unauthenticated firewall bypass via unfiltered IPv6 SSH

Published Mar 29, 2021 · Updated Aug 3, 2024

Firewall bypass in TP-Link Archer A7 before Archer A7(US)_V5_200220 allows remote attackers to reach IPv6 SSH without authentication. The IPv6 connection-handling path fails to apply the router's firewall filtering to SSH traffic, leaving the service reachable across the firewall. An unauthenticated network position is sufficient to bypass the filter; root code execution requires chaining this exposure with another vulnerability.

CVSS severity8.1
High
EPSS probability3.21%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Firewall bypass in TP-Link Archer A7 before Archer A7(US)_V5_200220 allows remote attackers to reach IPv6 SSH without authentication. The IPv6 connection-handling path fails to apply the router's firewall filtering to SSH traffic, leaving the service reachable across the firewall. An unauthenticated network position is sufficient to bypass the filter; root code execution requires chaining this exposure with another vulnerability.

The record

CVE
CVE-2021-27245
Published
Mar 29, 2021
Updated
Aug 3, 2024
Vendor
TP-Link
Product
Archer A7
Classifications
CWE-693, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 29, 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?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=prior to Archer C7(US)_V5_210125 and Archer A7(US)_V5_200220

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

TP-Link · Archer A7version=prior to Archer C7(US)_V5_210125 and Archer A7(US)_V5_200220

Published CVSS scores

8.1NIST NVDCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
9.3NIST NVDAV:N/AC:M/Au:N/C:C/I:C/A:C
8.1Zero Day InitiativeCVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

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 exploitUnconfirmed

Weakness, pattern, technique

CWE-693Protection Mechanism Failure
T1190Exploit Public-Facing Application

Public exploit references

No public exploit references are available in this record.

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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