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. 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: 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.
Sources
Enriched from CVE.org, FIRST EPSS, GitHub Security Advisories. Last verified by Threadlinqs on .