Nginx Gateway FabricWeb server / proxy · F5
CVE-2026-56434
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedNGINX Plus and NGINX Open Source have a vulnerability in the ngx_http_ssi_module module. This vulnerability may exist when the Server-Side Includes (SSI), proxy_pass, and proxy_buffering off directives are configured. With this configuration, an unauthenticated attacker with man-in-the-middle (MITM) ability to control responses from an upstream server may be able to cause a use-after-free in the NGINX worker process. This issue may lead to limited modification of memory or a restart of the NGINX worker process. Impact: This vulnerability may allow remote attackers to have limited control to modify memory contents or restart the NGINX worker process. There is no control plane exposure; this is a data plane issue only. Note: Software versions which have reached End of Technical Support (EoTS) are not evaluated.
In the news
Third-party coverageSurfaced from public web coverage — external links open in a new tab.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceA use-after-free vulnerability exists in NGINX's ngx_http_ssi_module when Server-Side Includes (SSI), proxy_pass, and proxy_buffering off directives are used together. An attacker with man-in-the-middle capability controlling upstream server responses can trigger this memory corruption, leading to limited memory modification or NGINX worker process restart.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data
Nginx Gateway FabricWeb server / proxy
>= 1.3.0, <= 1.6.2>= 2.0.0, < 2.6.7
Nginx Ingress ControllerWeb server / proxy
>= 3.5.0, <= 3.7.2>= 5.0.0, < 5.5.3>= 2026-lts-r1, < 2026-lts-r4= 4.0.0= 4.0.1
Nginx PlusWeb server / proxy
>= 37.0.0.1, < 37.0.3.1>= r33, < r36= r36
WafApplication
>= 4.11.0, <= 4.16.0>= 5.2.0, <= 5.8.0>= 5.9.0, < 5.13.4CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- High
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- Low
- Availability
- High
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:H
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Identify installed NGINX versionRun 'nginx -v' or 'nginx -V' to see the version numberAffected if Version is within the affected range (check NGINX security advisories for the specific patched version)
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Verify SSI is enabledSearch configuration files for 'ssi on;' directive within http, server, or location blocks, or confirm the ngx_http_ssi_module is loaded via 'nginx -V 2>&1 | grep -o ssi'Affected if SSI is actively enabled in the configuration
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Confirm proxy_pass is configuredSearch configuration files for 'proxy_pass' directives indicating reverse proxy setup to an upstream serverAffected if proxy_pass is configured and pointing to an upstream server
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Check proxy_buffering settingSearch configuration for 'proxy_buffering off;' directive - check http, server, and location blocks as it can be inherited or overriddenAffected if proxy_buffering is explicitly set to off (not just default)
The environment is affected if NGINX runs a vulnerable version with SSI enabled, proxy_pass configured, and proxy_buffering set to off simultaneously, allowing a man-in-the-middle attacker to trigger the use-after-free via crafted upstream responses
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
From vendor data2.6.75.5.35.13.4
Review NGINX configurations for the combination of SSI, proxy_pass, and proxy_buffering off directives; update NGINX to the latest version containing the security patch, or if immediate update is not feasible, evaluate disabling proxy_buffering or restructuring the SSI implementation to avoid the vulnerable configuration pattern.
Fix this in Nginx Gateway Fabric
Scoped from the published advisory
- Consultation2.0 h
- Implementation2.0 h
- Testing2.0 h
- Review / QA1.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,984.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-56434 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-56434 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Version or environment caveats, and links to real fixes
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