CVE-2021-44273Public exploitNetwork attack vector

TLS interception via omitted hostname verification

Published Dec 23, 2021 · Updated Aug 4, 2024

Improper certificate validation in e2guardian 5.4.0 through 5.4.3r allows man-in-the-middle attackers to intercept proxied TLS traffic. Socket::startSslClient sets the TLS SNI hostname but, with OpenSSL 1.1.x, fails to configure that hostname as the certificate verification target. The flaw is reachable only in standalone proxy or transparent-proxy deployments with SSL MITM enabled, where an on-path attacker can present any otherwise valid certificate and read or alter upstream traffic.

CVSS severity7.4
High
EPSS probability0.97%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper certificate validation in e2guardian 5.4.0 through 5.4.3r allows man-in-the-middle attackers to intercept proxied TLS traffic. Socket::startSslClient sets the TLS SNI hostname but, with OpenSSL 1.1.x, fails to configure that hostname as the certificate verification target. The flaw is reachable only in standalone proxy or transparent-proxy deployments with SSL MITM enabled, where an on-path attacker can present any otherwise valid certificate and read or alter upstream traffic.

The record

CVE
CVE-2021-44273
Published
Dec 23, 2021
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-295, T1557
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Dec 23, 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

5.8NIST NVDAV:N/AC:M/Au:N/C:P/I:P/A:N
7.4NIST NVDCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/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 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-295Improper Certificate Validation
T1557Adversary-in-the-Middle

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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