CVE-2021-20156Network attack vector

Firmware code execution via unsigned update images

Published Dec 30, 2021 · Updated Aug 3, 2024

Improper firmware verification in TRENDnet TEW-827DRU 2.08B01 allows attackers to install modified firmware through update workflows. The manual and automatic update paths accept firmware images without validating a cryptographic signature from a trusted source. Reaching the manual path requires administrator access, while the automatic path requires impersonating the update server; either path permits attacker-controlled firmware to run on the router.

CVSS severity6.5
Medium
EPSS probability0.41%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper firmware verification in TRENDnet TEW-827DRU 2.08B01 allows attackers to install modified firmware through update workflows. The manual and automatic update paths accept firmware images without validating a cryptographic signature from a trusted source. Reaching the manual path requires administrator access, while the automatic path requires impersonating the update server; either path permits attacker-controlled firmware to run on the router.

The record

CVE
CVE-2021-20156
Published
Dec 30, 2021
Updated
Aug 3, 2024
Vendor
TRENDnet
Product
TEW-827DRU Firmware
Classifications
CWE-347, T1542.001
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Dec 30, 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=2.08B01

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

TRENDnet · TEW-827DRU Firmwareversion=2.08B01

Published CVSS scores

4.0NIST NVDAV:N/AC:L/Au:S/C:N/I:P/A:N
6.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-347Improper Verification of Cryptographic Signature
T1542.001Pre-OS Boot: System Firmware

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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