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Review reviewCritical

CVE-2026-42055

F5 NGINX Open Source, NGINX Plus, Red Hat Enterprise Linux 10

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 res...

CVSS
9.2
EPSS
4.04%
89.6% percentile
CISA KEV
Not listed
Published
2026.06.18
PRIORITY ASSESSMENT

Review review

The CVSS severity warrants an early asset and exposure review.

Known exploitationNot established by KEV
Exploit probability4.04%
Technical severityCVSS 9.2

Vulnerability overview

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 res...

Affected product and versions

Product
F5 NGINX Open Source, NGINX Plus, Red Hat Enterprise Linux 10
Affected versions
>= 1.13.10 < 1.31.2, >= 1.30.2 < 1.30.3, >= 37.0 < 37.0.2.1, >= R36 < R36 P6, 4.9.0, >= 4.3.0 <= 4.7.0, >= 4.10.0 <= 4.16.0, >= 5.2.0 <= 5.8.0, >= 1.3.0 <= 1.6.2, >= 2.0.0 < 2.6.4, >= 3.5.0 <= 3.7.2, >= 5.0.0 < 5.5.1, 4.0.0, 4.0.1, >= 2.17.0 <= 2.22.0, >= 1.30.0 < 1.30.3, 1.31.1, >= 37.0.0 <= 37.0.1, r3, r30
Fixed versions
2.6.4, 5.5.1, 1.30.3

Recommended response sequence

Confirm exposure before applying a vendor-supported change.

Full remediation guide
  1. 1
    Identify

    Confirm that F5 NGINX Open Source, NGINX Plus, Red Hat Enterprise Linux 10 and an affected version are present.

  2. 2
    Prioritize

    Combine exploitation signals with asset exposure and business criticality.

  3. 3
    Remediate

    Follow the vendor advisory or supported update path and preserve rollback options.

  4. 4
    Verify

    Recheck the version, service health, access paths, and relevant logs.

Technical data

CVSS vector
CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
CWE
CWE-122, CWE-131, CWE-787