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Review reviewCritical

CVE-2026-9256

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

NGINX Plus and NGINX Open Source have a vulnerability in the ngx_http_rewrite_module module. This vulnerability exists when a rewrite directive uses a regex pattern with distinct, overlapping Perl-Compatible Regular Expression (PCRE) captures (for example, ^/((.*))$) and a replacement string that references multiple such captures (for example, $1$2) in a redirect or arguments context. An unauthenticated attacker along with conditions beyond their control can exploit this vulnerability by sending crafted HTTP requests. This may cause a heap buffer overflow in the NGINX worker process leading...

CVSS
9.2
EPSS
4.26%
89.9% percentile
CISA KEV
Not listed
Published
2026.05.23
PRIORITY ASSESSMENT

Review review

The CVSS severity warrants an early asset and exposure review.

Known exploitationNot established by KEV
Exploit probability4.26%
Technical severityCVSS 9.2

Vulnerability overview

NGINX Plus and NGINX Open Source have a vulnerability in the ngx_http_rewrite_module module. This vulnerability exists when a rewrite directive uses a regex pattern with distinct, overlapping Perl-Compatible Regular Expression (PCRE) captures (for example, ^/((.*))$) and a replacement string that references multiple such captures (for example, $1$2) in a redirect or arguments context. An unauthenticated attacker along with conditions beyond their control can exploit this vulnerability by sending crafted HTTP requests. This may cause a heap buffer overflow in the NGINX worker process leading...

Affected product and versions

Product
F5 NGINX Plus, NGINX Open Source, Red Hat Enterprise Linux 10
Affected versions
>= 37.0 < 37.0.1.1, >= R36 < R36 P5, >= R32 < R32 P7, >= 1.31.0 < 1.31.1, >= 1.30.0 < 1.30.2, >= 0.1.17 <= 0.9.7, >= 1.0.0 <= 1.30.1, 1.31.0, >= 37.0.0 < 37.0.1.1, >= r32 <= r36
Fixed versions
37.0.1.1

Recommended response sequence

Confirm exposure before applying a vendor-supported change.

Full remediation guide
  1. 1
    Identify

    Confirm that F5 NGINX Plus, NGINX Open Source, 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
CVE-2026-9256 — F5 NGINX Plus, NGINX Open Source, Red Hat Enterprise Linux 10 | SECUFOCUS NOW