CVE-2026-42055: F5 Nginx Plus buffer overflow (CVSS 8.1)

Description

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.

CVSS 3.1 breakdown

Attack vectorNetwork

Attack complexityHigh

Privileges requiredNone

User interactionNone

ScopeUnchanged

ConfidentialityHigh

IntegrityHigh

AvailabilityHigh

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected products

F5 Dos4.9.0 · ≥ 4.3.0 ≤ 4.7.0

F5 Nginx Gateway Fabric≥ 1.3.0 ≤ 1.6.2 · ≥ 2.0.0 ≤ 2.6.3

F5 Nginx Ingress Controller≥ 3.5.0 ≤ 3.7.2 · ≥ 4.0.0 ≤ 4.0.1 · ≥ 5.0.0 ≤ 5.5.0

F5 Nginx Instance Manager≥ 2.17.0 ≤ 2.22.0

F5 Nginx Open Source≥ 1.0.0 ≤ 1.30.2 · ≥ 1.31.0 ≤ 1.31.1

F5 Nginx Plus≥ r33 < r36 · ≥ 37.0.0.1 < 37.0.2.1 · r36

F5 Waf≥ 4.10.0 ≤ 4.16.0 · ≥ 5.2.0 ≤ 5.8.0 · ≥ 5.9.0 ≤ 5.13.1

Redhat Discoveryall versions

Redhat Hardened Imagesall versions

Redhat Update Infrastructure≥ 5.0 < 5.2

Redhat Enterprise Linux10.0 · 8.0 · 9.0

Remediation

Fixed in

F5 Nginx Plus≥ r36

Redhat Update Infrastructure≥ 5.2

Patch & vendor advisories

https://my.f5.com/manage/s/article/K000161584

References

https://access.redhat.com/errata/RHSA-2026:27197Third Party Advisory
https://access.redhat.com/errata/RHSA-2026:36331Third Party Advisory
https://access.redhat.com/errata/RHSA-2026:36364Third Party Advisory
https://access.redhat.com/errata/RHSA-2026:36618Third Party Advisory
https://access.redhat.com/errata/RHSA-2026:36639Third Party Advisory
https://access.redhat.com/errata/RHSA-2026:38847Third Party Advisory
https://access.redhat.com/errata/RHSA-2026:44481Third Party Advisory
https://access.redhat.com/errata/RHSA-2026:46836Third Party Advisory
https://access.redhat.com/errata/RHSA-2026:58981
https://access.redhat.com/security/cve/CVE-2026-42055Third Party Advisory

and 3 more references

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Frequently asked

Is CVE-2026-42055 being actively exploited?

CVE-2026-42055 is not in the CISA KEV catalog. Its EPSS exploit probability is 6.54%.

How severe is CVE-2026-42055?

CVE-2026-42055 has a CVSS 3.1 base score of 8.1, rated high. EPSS estimates a 6.54% probability of exploitation.

Which products are affected by CVE-2026-42055?

Affected products include F5 Dos, F5 Nginx Gateway Fabric, F5 Nginx Ingress Controller, F5 Nginx Instance Manager, F5 Nginx Open Source, and 6 more.

How do I fix CVE-2026-42055?

Upgrade affected software to a fixed version, for example F5 Nginx Plus r36, Redhat Update Infrastructure 5.2 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2026-42055 against the real software inventory on every managed device, every day. Rather than a static severity, each match is scored in context: exploit availability, EPSS, the asset's exposure, and business criticality decide where it lands in the queue. If an affected version is present anywhere across your portfolio, it surfaces automatically with a prioritised remediation path.

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