CVE-2026-56434Network attack vector

Worker restart via SSI use-after-free

Published Jul 15, 2026 · Updated Jul 15, 2026

Use-after-free in F5 NGINX Open Source and NGINX Plus allows remote attackers to restart a worker via upstream responses. The ngx_http_ssi_module response path accesses freed worker memory while processing unbuffered proxied data with SSI enabled. Exploitation requires control of upstream responses from a man-in-the-middle position; impact is limited to memory modification or worker restart, with no control-plane exposure.

CVSS severity8.3
High
EPSS probability0.45%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Use-after-free in F5 NGINX Open Source and NGINX Plus allows remote attackers to restart a worker via upstream responses. The ngx_http_ssi_module response path accesses freed worker memory while processing unbuffered proxied data with SSI enabled. Exploitation requires control of upstream responses from a man-in-the-middle position; impact is limited to memory modification or worker restart, with no control-plane exposure.

The record

CVE
CVE-2026-56434
Published
Jul 15, 2026
Updated
Jul 15, 2026
Vendor
F5 Networks
Product
NGINX Open Source
Classifications
CWE-416, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 15, 2026CVE publishedPublication date reported by the CVE source.
  2. Jul 15, 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=0.8.11 <1.30.4
  2. Affected versionversion=1.31.2 <1.31.3

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

F5 Networks · NGINX Open Sourceversion=0.8.11 <1.30.4; version=1.31.2 <1.31.3
F5 Networks · NGINX Plusversion=37.0.0.1 <37.0.3.1; version=R33 <*; version=R36 <R36 P7

Published CVSS scores

6.5F5 NetworksCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:H
8.3F5 NetworksCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:H/SC:N/SI:N/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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

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
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-416Use After Free
T1499.004Endpoint Denial of Service: Application or System Exploitation

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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