CVE-2026-39998Network attack vector

Identity spoofing via uncleared upstream headers

Published Jun 19, 2026 · Updated Jun 19, 2026

Improper input validation in Apache APISIX 2.12.0 through 3.16.0 allows remote authenticated users to spoof upstream identities. The forward-auth plugin leaves a client-supplied header named in upstream_headers intact when the authorization service returns HTTP 200 without that header. Exploitation requires an enabled forward-auth route with a trusted upstream identity header, allowing the client value to reach the upstream application as authenticated identity data.

CVSS severity5.8
Medium
EPSS probability0.68%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper input validation in Apache APISIX 2.12.0 through 3.16.0 allows remote authenticated users to spoof upstream identities. The forward-auth plugin leaves a client-supplied header named in upstream_headers intact when the authorization service returns HTTP 200 without that header. Exploitation requires an enabled forward-auth route with a trusted upstream identity header, allowing the client value to reach the upstream application as authenticated identity data.

The record

CVE
CVE-2026-39998
Published
Jun 19, 2026
Updated
Jun 19, 2026
Vendor
The Apache Software Foundation
Product
Apache APISIX
Classifications
CWE-20, T1190
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Jun 19, 2026CVE publishedPublication date reported by the CVE source.
  2. Jun 19, 2026Record 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=2.12.0 <=3.16.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

The Apache Software Foundation · Apache APISIXversion=2.12.0 <=3.16.0

Published CVSS scores

8.8NIST National Vulnerability DatabaseCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
5.8Apache Software FoundationCVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:N/VI:N/VA:N/SC:H/SI:H/SA: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.

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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
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-20Improper Input Validation
T1190Exploit Public-Facing Application

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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