High Memory corruption

CVE-2026-42055 — NGINX ngx_http_proxy_v2_module and ngx_http_grpc_module vulnerability

NGINX Plus and NGINX Open Source have a vulnerability in the ngx_http_proxy_v2_module and ngx_http_grpc_module modules. This vulnerability exists when the proxy_http_version to 2 or grpc_pass directives are used to proxy HTTP/2 traffic, the ignore_invalid_headers directive is set to off, and the large_client_header_buffers directive size is larger than 2 megabytes. A remote, unauthenticated attacker, along with conditions beyond their control, could send large headers while creating an upstream request. This may cause a heap-based buffer overflow in the NGINX worker process leading to a restart. Additionally, attackers can execute code on systems with Address Space Layout Randomization (ASLR) disabled or when the attacker can bypass ASLR. Note: Software versions which have reached End of Technical Support (EoTS) are not evaluated.

Published Jun 17, 2026 · Updated Oct 13, 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

EPSS 6.5% (30-day exploitation probability)+14
Technical severity (high)+6

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

6.54%

ahead of 94% of scored CVEs · Oct 15, 2026

Affects

Dos and 10 more

CVSS base

8.1

High · 3 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

Total

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 Dos, F5 Nginx Gateway Fabric, F5 Nginx Ingress Controller…).
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.
EPSS ahead of 94% of scored CVEs: prioritize it in the patch queue.
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	Dos	version 4.9.0≥ 4.3.0 and ≤ 4.7.0	Vulnerable	NIST National Vulnerability Database
F5	Nginx Gateway Fabric	≥ 2.0.0 and ≤ 2.6.3≥ 1.3.0 and ≤ 1.6.2	Vulnerable	NIST National Vulnerability Database
F5	Nginx Ingress Controller	≥ 3.5.0 and ≤ 3.7.2≥ 4.0.0 and ≤ 4.0.1≥ 5.0.0 and ≤ 5.5.0	Vulnerable	NIST National Vulnerability Database
F5	Nginx Instance Manager	≥ 2.17.0 and ≤ 2.22.0	Vulnerable	NIST National Vulnerability Database
F5	Nginx Open Source	≥ 1.30.2 and < 1.30.3≥ 1.13.10 and < 1.31.2	Vulnerable	CVE Program (cve.org) e CISA ADP
F5	Nginx Open Source	≥ 1.31.0 and ≤ 1.31.1≥ 1.0.0 and ≤ 1.30.2	Vulnerable	NIST National Vulnerability Database
F5	Nginx Plus	version r36-p4version r36-p5version r36-p3version r36-p2version r36-p1version r36≥ r33 and < r36≥ 37.0.0.1 and < 37.0.2.1	Vulnerable	NIST National Vulnerability Database
F5	Nginx Plus	≥ R36 and < R36 P6≥ 37.0 and < 37.0.2.1	Vulnerable	CVE Program (cve.org) e CISA ADP
F5	Waf	≥ 4.10.0 and ≤ 4.16.0≥ 5.2.0 and ≤ 5.8.0≥ 5.9.0 and ≤ 5.13.1	Vulnerable	NIST National Vulnerability Database
Red Hat	Discovery	versions not specified by the source	Vulnerable	NIST National Vulnerability Database
Red Hat	Enterprise Linux	version 10.0version 9.0version 8.0	Vulnerable	NIST National Vulnerability Database
Red Hat	Hardened Images	versions not specified by the source	Vulnerable	NIST National Vulnerability Database
Red Hat	Update Infrastructure	≥ 5.0 and < 5.2	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

High

Integrity

High

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
9.2	CVSS 4.0	Critical	—	—	f5sirt@f5.com via NIST National Vulnerability Database
9.2	CVSS 4.0	Critical	—	—	f5 via CVE Program (cve.org) e CISA ADP
8.1	CVSS 3.1	High	2.2	5.9	f5sirt@f5.com via NIST National Vulnerability Database
8.1	CVSS 3.1	High	2.2	5.9	0b0ca135-0b70-47e7-9f44-1890c2a1c46c via NIST National Vulnerability Database
8.1	CVSS 3.1	High	—	—	f5 via CVE Program (cve.org) e CISA ADP

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

Weakness MITRE

Weakness class according to MITRE’s CWE catalog.

CWE-787 · Out-of-bounds Write

Other CVEs with this weakness →

EPSS over time FIRST

Oct 13, 2026 → Oct 15, 2026 · 3 reading(s) · max 6.54%

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 open source, f5/nginx plus
Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
SSVC assessment updated
Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
Record published
Oct 13, 2026
CVSS changed · 8.1
Oct 13, 2026 · NIST National Vulnerability Database
Source status changed · → Modified
Oct 13, 2026 · NIST National Vulnerability Database
Record created in this database
Oct 13, 2026 · NIST National Vulnerability Database
CVE published
Jun 17, 2026 · f5

Source activity

Repeated readings are counted rather than listed.

1× Official description updated · Oct 13, 2026 – Oct 13, 2026

References

13 on the record

my.f5.com/manage/s/article/K000161584
Vendor Advisory, vendor-advisory, NIST National Vulnerability Database
access.redhat.com/errata/RHSA-2026:36364
Third Party Advisory, NIST National Vulnerability Database
access.redhat.com/errata/RHSA-2026:27197
Third Party Advisory, NIST National Vulnerability Database
access.redhat.com/errata/RHSA-2026:46836
Third Party Advisory, NIST National Vulnerability Database
bugzilla.redhat.com/show_bug.cgi
Issue Tracking, Third Party Advisory, NIST National Vulnerability Database
security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-42055.json
Third Party Advisory, NIST National Vulnerability Database
access.redhat.com/errata/RHSA-2026:36618
Third Party Advisory, NIST National Vulnerability Database
access.redhat.com/errata/RHSA-2026:36639
Third Party Advisory, NIST National Vulnerability Database
access.redhat.com/errata/RHSA-2026:44481
Third Party Advisory, NIST National Vulnerability Database
access.redhat.com/security/cve/CVE-2026-42055
Third Party Advisory, NIST National Vulnerability Database
access.redhat.com/errata/RHSA-2026:58981
NIST National Vulnerability Database
access.redhat.com/errata/RHSA-2026:38847
Third Party Advisory, NIST National Vulnerability Database
access.redhat.com/errata/RHSA-2026:36331
Third Party Advisory, NIST National Vulnerability Database

Elsewhere on this site

F5
every CVE for this vendor

Memory corruption
same class

CWE-787
other pages naming this weakness

Related CVEs (same products)

Medium CVE-2026-110924 Openssh: openssh: gssapi delegated credentials can be stored after a failed authentication 1d
Medium CVE-2026-110927 Openssh: openssh: a compressed payload can expand past the maximum packet size 1d
Medium CVE-2026-110926 Openssh: openssh: shared lz77 compression dictionary leaks plaintext across channels 1d
Medium CVE-2026-110925 Openssh: openssh: '$' and '\' in a command-line username expand through %u 1d
Medium CVE-2026-110923 Openssh: openssh: sftp can write outside the destination directory from a server-supplied path 1d
High CVE-2026-97205 NGINX ngx_http_core_module vulnerability 2d

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 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-2026-42055 is "NGINX ngx_http_proxy_v2_module and ngx_http_grpc_module vulnerability", rated High. It affects Dos (F5); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 8.1 describes technical severity. EPSS 6.54% estimates the probability of exploitation in 30 days; neither replaces your asset context. 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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