CVE-2026-42926: CWE-172 Encoding Error in F5 NGINX Open Source
When NGINX Open Source is configured to proxy HTTP/2 traffic by setting proxy_http_version to 2, and also uses proxy_set_body, an attacker may be able to inject frame headers and payload bytes to the upstream peer. Note: Software versions which have reached End of Technical Support (EoTS) are not evaluated.
AI Analysis
Technical Summary
This vulnerability (CVE-2026-42926) involves an encoding error (CWE-172) in F5 NGINX Open Source 1.29.4 when configured to proxy HTTP/2 traffic (proxy_http_version=2) and using proxy_set_body. Under these conditions, an attacker may inject frame headers and payload bytes to the upstream peer, potentially impacting data integrity. The CVSS v3.1 base score is 5.8 (medium severity), reflecting network attack vector, low attack complexity, no privileges or user interaction required, and a scope change. No official patch or remediation guidance is currently available, and the vulnerability is published but not yet addressed by the vendor.
Potential Impact
The vulnerability allows an attacker to inject data into HTTP/2 frames sent to upstream servers, potentially altering the integrity of proxied requests. There is no impact on confidentiality or availability according to the CVSS vector. No known exploits have been observed in the wild. The vulnerability affects only the specified version 1.29.4 of NGINX Open Source when configured in the described manner.
Mitigation Recommendations
Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until an official fix is released, users should review their proxy_http_version and proxy_set_body configurations to assess exposure. No vendor-provided mitigation or temporary fix is currently available.
CVE-2026-42926: CWE-172 Encoding Error in F5 NGINX Open Source
Description
When NGINX Open Source is configured to proxy HTTP/2 traffic by setting proxy_http_version to 2, and also uses proxy_set_body, an attacker may be able to inject frame headers and payload bytes to the upstream peer. Note: Software versions which have reached End of Technical Support (EoTS) are not evaluated.
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
This vulnerability (CVE-2026-42926) involves an encoding error (CWE-172) in F5 NGINX Open Source 1.29.4 when configured to proxy HTTP/2 traffic (proxy_http_version=2) and using proxy_set_body. Under these conditions, an attacker may inject frame headers and payload bytes to the upstream peer, potentially impacting data integrity. The CVSS v3.1 base score is 5.8 (medium severity), reflecting network attack vector, low attack complexity, no privileges or user interaction required, and a scope change. No official patch or remediation guidance is currently available, and the vulnerability is published but not yet addressed by the vendor.
Potential Impact
The vulnerability allows an attacker to inject data into HTTP/2 frames sent to upstream servers, potentially altering the integrity of proxied requests. There is no impact on confidentiality or availability according to the CVSS vector. No known exploits have been observed in the wild. The vulnerability affects only the specified version 1.29.4 of NGINX Open Source when configured in the described manner.
Mitigation Recommendations
Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until an official fix is released, users should review their proxy_http_version and proxy_set_body configurations to assess exposure. No vendor-provided mitigation or temporary fix is currently available.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- f5
- Date Reserved
- 2026-05-05T21:19:09.531Z
- Cvss Version
- 3.1
- State
- PUBLISHED
- Remediation Level
- null
Threat ID: 6a049717cbff5d8610e00312
Added to database: 5/13/2026, 3:21:59 PM
Last enriched: 5/13/2026, 3:39:07 PM
Last updated: 5/14/2026, 6:48:16 AM
Views: 4
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