CVE-2023-28803

Traffic inspection bypass via synthetic IP spoofing

Published Oct 23, 2023 · Updated Sep 11, 2024

Authentication bypass in Zscaler Client Connector before 3.9 on Windows allows adjacent attackers to bypass protected traffic. The client treats a device that spoofs an address in its synthetic IP range as part of the local network, causing traffic to evade enforced routing. Exploitation requires adjacency to the endpoint's network and control of a spoofed synthetic address; the bounded impact is bypass of the connector's traffic protections.

CVSS severity5.9
Medium
EPSS probability0.26%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Authentication bypass in Zscaler Client Connector before 3.9 on Windows allows adjacent attackers to bypass protected traffic. The client treats a device that spoofs an address in its synthetic IP range as part of the local network, causing traffic to evade enforced routing. Exploitation requires adjacency to the endpoint's network and control of a spoofed synthetic address; the bounded impact is bypass of the connector's traffic protections.

The record

CVE
CVE-2023-28803
Published
Oct 23, 2023
Updated
Sep 11, 2024
Vendor
Zscaler
Product
Zscaler Client Connector
Classifications
CWE-290, T1562.001
Attack vector
adjacent
Privileges
unauthenticated

Timeline

How it unfolded

  1. Oct 23, 2023CVE publishedPublication date reported by the CVE source.
  2. Sep 11, 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=0 <3.9

What conditions does exploitation require?

Attack vectoradjacent
Required privilegesunauthenticated

What is affected?

Zscaler · Zscaler Client Connectorversion=0 <3.9

Published CVSS scores

5.9Zscaler, Inc.CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:N
6.5NIST NVDCVSS:3.1/AV:A/AC:L/PR:N/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)
Vectoradjacent
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-290Authentication Bypass by Spoofing
T1562.001Impair Defenses: Disable or Modify Tools

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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