# CVE-2026-56434 — F5 NGINX Plus

> As of 2026-07-15, CVE-2026-56434 is a MEDIUM-severity vulnerability in F5 NGINX Plus, CVSS v3.1 6.5, EPSS 0.4% (34.2th percentile). Threadlinqs Intelligence links 1 tracked threat campaign to CVE-2026-56434, most recently “F5 Patches Multiple NGINX Vulnerabilities: Heap Overflow, Memory Disclosure, and Use-After-Free (CVE-2026-42533, CVE-2026-60005, CVE-2026-56434)”.

**Last updated:** 2026-07-15

## What is CVE-2026-56434?

NGINX 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.

The record classifies CVE-2026-56434 under weakness class [CWE-416](https://intel.threadlinqs.com/cwe/CWE-416). Its CVSS v3 base vector states that the flaw is reachable remotely over the network, needs no prior authentication, needs no user interaction, and has high impact on availability. 2 affected-product entries are recorded, across 1 vendor, listed below. The identifier was first published 104 days ago.

## Severity and exploitation probability

- **CVSS v3.1 base score:** 6.5 — MEDIUM (`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:H`)
- **CVSS v4.0 base score:** 8.3 (`CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:H/SC:N/SI:N/SA:N`)
- **EPSS (FIRST):** 0.4% probability of exploitation in the next 30 days, higher than 34.2% of all scored CVEs
- **CISA KEV:** Not listed in the CISA Known Exploited Vulnerabilities catalog
- **Threadlinqs priority:** 4.6/10 — a Threadlinqs composite of the CVSS base score, the EPSS percentile and public exploit availability
- **Published:** 2026-07-15

## Is CVE-2026-56434 being exploited?

It currently carries a trending score of 22 in the Threadlinqs vulnerability feed.

## Affected products and versions

- [F5](https://intel.threadlinqs.com/vendors/f5): NGINX Plus, NGINX Open Source

## How to fix CVE-2026-56434

No vendor patch reference has been recorded for CVE-2026-56434 in the tracked sources. Follow the references below for a fix, and treat the products listed above as exposed until the vendor states otherwise.

## Threat activity tracking CVE-2026-56434

1 tracked threat in the Threadlinqs corpus references CVE-2026-56434, either in the campaign’s CVE list or as an indicator on the campaign record.

- [F5 Patches Multiple NGINX Vulnerabilities: Heap Overflow, Memory Disclosure, and Use-After-Free (CVE-2026-42533, CVE-2026-60005, CVE-2026-56434)](https://intel.threadlinqs.com/threat/TL-2026-1391) — CRITICAL · 2026-07-15

## Sources

Enriched from CVE.org, FIRST EPSS, GitHub Security Advisories. Last verified by Threadlinqs on 2026-10-10.

**Vendor advisory and patch**

- [my.f5.com — vendor advisory](https://my.f5.com/manage/s/article/K000162098)

Canonical: https://intel.threadlinqs.com/cve/CVE-2026-56434
Full detection coverage and IOCs for threats exploiting CVE-2026-56434 via the Threadlinqs MCP server (Purple tier): https://intel.threadlinqs.com/mcp