CVE-2026-42926Public exploitNetwork attack vector

Upstream request injection via truncated frame length

Published May 13, 2026 · Updated May 13, 2026

HTTP/2 request injection in ngx_http_proxy_v2_module in F5 NGINX Open Source 1.29.4 through 1.30.0 allows remote attackers to alter upstream requests. The module writes only the low 24 bits of a generated proxy_set_body length into the HTTP/2 DATA frame header but appends the full body. Exploitation requires both proxy_http_version 2 and proxy_set_body; overflow bytes are interpreted by the upstream peer as frame headers and payload.

CVSS severity5.8
Medium
EPSS probability0.35%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

HTTP/2 request injection in ngx_http_proxy_v2_module in F5 NGINX Open Source 1.29.4 through 1.30.0 allows remote attackers to alter upstream requests. The module writes only the low 24 bits of a generated proxy_set_body length into the HTTP/2 DATA frame header but appends the full body. Exploitation requires both proxy_http_version 2 and proxy_set_body; overflow bytes are interpreted by the upstream peer as frame headers and payload.

The record

CVE
CVE-2026-42926
Published
May 13, 2026
Updated
May 13, 2026
Vendor
F5 Networks
Product
NGINX Open Source
Classifications
CWE-172, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 13, 2026CVE publishedPublication date reported by the CVE source.
  2. May 13, 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=1.29.4 <1.30.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

F5 Networks · NGINX Open Sourceversion=1.29.4 <1.30.1

Published CVSS scores

5.8F5CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N
6.3F5CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:L/SA: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.

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No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-172Encoding Error
T1190Exploit Public-Facing Application

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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