CVE-2026-39998 Apache Software Foundation CVE debrief

Who should care

Defenders of Apache APISIX installations, particularly those using versions between 2.12.0 and 3.16.0, should be aware of this vulnerability. Upgrading to version 3.17.0 is recommended to mitigate the risk of identity header spoofing.

Technical summary

The CVE-2026-39998 vulnerability in Apache APISIX arises from improper input validation in the forward-auth plugin. This allows attackers to spoof identity headers under certain configurations. The vulnerability affects Apache APISIX versions from 2.12.0 to 3.16.0. The CVSS vector is CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:N/VI:N/VA:N/SC:H/SI:H/SA:H/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X, indicating a Medium severity with a score of 5.8.

Defensive priority

Medium priority due to potential for header spoofing with CVSS score of 5.8

Recommended defensive actions

• Inventory Apache APISIX installations to identify affected versions.
• Review and upgrade vulnerable Apache APISIX instances to version 3.17.0.
• Monitor for unusual identity header activity.
• Implement compensating controls to validate identity headers.
• Review forward-auth plugin configurations for potential vulnerabilities.

Evidence notes

The primary evidence for CVE-2026-39998 comes from the NVD and CVE.org records. The vulnerability affects Apache APISIX versions 2.12.0 through 3.16.0. Defenders should verify their APISIX versions and configurations to assess exposure.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.