Medium Memory corruption

CVE-2026-56434 — NGINX ngx_http_ssi_module vulnerability

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.

Published Jul 15, 2026 · Updated Oct 15, 2026 · Sources: NIST National Vulnerability Database, CVE Program (cve.org) e CISA ADP · CNA: f5

Low

Who exploits it and how urgent it is

A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.

No exploitation signal in the sources consulted so far.

How the score was calculated

Technical severity (medium)+3

The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

Exploitation

Not confirmed

Not in CISA KEV — an absence of record, not proof it is unexploited.

EPSS FIRST

—

No EPSS score.

Affects

Nginx Gateway Fabric and 4 more

CVSS base

6.5

Medium · 2 source(s)

CISA SSVC assessment CISA

Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.

Exploitation

None

none · proof-of-concept · active

Automatable

can an attacker script the kill-chain steps

Technical impact

Partial

partial · total control of the vulnerable component

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

No fix documented by the sources we poll. That does not mean none exists: check the vendor advisory.

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

Identify exposed assets running the affected vendor/product/version combinations (F5 Nginx Gateway Fabric, F5 Nginx Ingress Controller, F5 Nginx Open Source…).
The attack is network-based and needs no privileges: restrict exposure (ACLs, VPN, WAF) until patched.
No fix documented in the sources: reduce exposure and monitor the vendor advisory.
Search available logs for exploit probes matching the vulnerability class (memory corruption), errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

Vendor	Product	Versions	Status	Source
F5	Nginx Gateway Fabric	≥ 2.0.0 and < 2.6.7≥ 1.3.0 and ≤ 1.6.2	Vulnerable	NIST National Vulnerability Database
F5	Nginx Ingress Controller	≥ 5.0.0 and < 5.5.3≥ 2026-lts-r1 and < 2026-lts-r4version 4.0.0version 4.0.1≥ 3.5.0 and ≤ 3.7.2	Vulnerable	NIST National Vulnerability Database
F5	Nginx Open Source	≥ 0.8.11 and < 1.30.4≥ 1.31.2 and < 1.31.3	Vulnerable	CVE Program (cve.org) e CISA ADP
F5	Nginx Plus	version r36-p5version r36-p6version r36-p4version r36-p3version r36-p2version r36-p1version r36≥ r33 and < r36 and 1 more ≥ 37.0.0.1 and < 37.0.3.1	Vulnerable	NIST National Vulnerability Database
F5	Nginx Plus	≥ R33≥ R36 and < R36 P7≥ 37.0.0.1 and < 37.0.3.1	Vulnerable	CVE Program (cve.org) e CISA ADP
F5	Waf	≥ 4.11.0 and ≤ 4.16.0≥ 5.2.0 and ≤ 5.8.0≥ 5.9.0 and < 5.13.4	Vulnerable	NIST National Vulnerability Database

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Attack vector

Network

Attack complexity

High

Privileges required

None

User interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

Low

Availability

High

Every base score collected

Sources score independently and may disagree; each row says who scored it and under which version.

Score	Version	Severity	Expl.	Impact	Scored by
8.3	CVSS 4.0	High	—	—	f5sirt@f5.com via NIST National Vulnerability Database
8.3	CVSS 4.0	High	—	—	f5 via CVE Program (cve.org) e CISA ADP
6.5	CVSS 3.1	Medium	2.2	4.2	f5sirt@f5.com via NIST National Vulnerability Database
6.5	CVSS 3.1	Medium	—	—	f5 via CVE Program (cve.org) e CISA ADP

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:H (score shown at the top: f5sirt@f5.com)

Weakness MITRE

Weakness class according to MITRE’s CWE catalog.

CWE-416 · Use After Free

Other CVEs with this weakness →

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).
Correlate service crashes/restarts with inbound traffic; repeated crashes may indicate attempts.

web/proxy/WAF logsnetwork IDS/IPSendpoint telemetry (EDR)crash dumps

Timeline

What happened to this CVE, newest first.

2026
Affected products added · f5/nginx plus, f5/nginx open source
Oct 15, 2026 · CVE Program (cve.org) e CISA ADP
SSVC assessment updated
Oct 15, 2026 · CVE Program (cve.org) e CISA ADP
Record published
Oct 15, 2026
CVSS changed · 6.5
Oct 15, 2026 · NIST National Vulnerability Database
Source status changed · → Analyzed
Oct 15, 2026 · NIST National Vulnerability Database
Record created in this database
Oct 15, 2026 · NIST National Vulnerability Database
CVE published
Jul 15, 2026 · f5

Source activity

Repeated readings are counted rather than listed.

1× Official description updated · Oct 15, 2026 – Oct 15, 2026

References

1 on the record

my.f5.com/manage/s/article/K000162098
Vendor Advisory, vendor-advisory, patch, NIST National Vulnerability Database

Elsewhere on this site

F5
every CVE for this vendor

Memory corruption
same class

CWE-416
other pages naming this weakness

Related CVEs (same products)

Medium CVE-2026-96615 NGINX Gateway Fabric vulnerability 1d
Medium CVE-2026-97629 NGINX ngx_http_ssl_module vulnerability 1d
High CVE-2026-97205 NGINX ngx_http_core_module vulnerability 1d
Medium CVE-2026-95101 NGINX ngx_http_v3_module vulnerability 1d
High CVE-2026-94197 NGINX Ingress Controller vulnerability 1d
High CVE-2026-93479 NGINX map directive and regex matching vulnerability 1d

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

No FIRST EPSS score.
No fixed version, patch or mitigation documented.
No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2026-56434 is "NGINX ngx_http_ssi_module vulnerability", rated Medium. It affects Nginx Gateway Fabric (F5); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 6.5 describes technical severity. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

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