THREATPORT/VULNERABILITY/CVE-2026-9256
HIGH SEVERITY

CVE-2026-9256

Nginx Open Source vulnerability

CVSS
8.1
EPSS
4.3%
EPSS pct
90th
Exploited
No known
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 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.
Affected vendor
F5
Affected product
Nginx Open Source
CVSS vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
Weakness type (CWE)
  • CWE-122 — Heap-based Buffer Overflow
Published
2026-05-22

Risk analysis

Based on its CVSS vector, this vulnerability is exploitable over the network, high attack complexity, requiring no privileges, no user interaction. Successful exploitation leads to high impact to confidentiality, high impact to integrity, high impact to availability.

Its EPSS score of 4.3% reflects a lower probability of exploitation activity in the wild over the next 30 days, placing it above 90% of all scored CVEs.

Check your external exposure to CVE-2026-9256

  • Confirm whether F5 Nginx Open Source is running on any internet-facing host or subdomain.
  • Match discovered service fingerprints against the version affected by CVE-2026-9256.
  • Prioritise remediation if the asset is public, business-critical, or near authentication/payment flows.

How ThreatPort helps with CVE-2026-9256

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