CVE Intelligence
High Memory corruption

CVE-2026-9256 — NGINX ngx_http_rewrite_module vulnerability

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.

Published May 22, 2026 · Updated Oct 13, 2026 · Sources: NIST National Vulnerability Database, CVE Program (cve.org) e CISA ADP · CNA: f5

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 2.7% (30-day exploitation probability)+13
  • 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
2.7%
ahead of 86% of scored CVEs · Oct 14, 2026
Affects
Debian
Debian Linux and 11 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
No
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.

  • Documented mitigation — my.f5.com (NIST National Vulnerability Database)

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.

  1. Identify exposed assets running the affected vendor/product/version combinations (Debian Debian Linux, F5 Dos, F5 Nginx Gateway Fabric…).
  2. The attack is network-based and needs no privileges: restrict exposure (ACLs, VPN, WAF) until patched.
  3. Apply the documented mitigations until a definitive fix is available.
  4. 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.

VendorProductVersionsStatusSource
Debian Debian Linux version 11.0 Vulnerable NIST National Vulnerability Database
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 < 2.6.2≥ 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 < 5.4.3 Vulnerable NIST National Vulnerability Database
F5 Nginx Instance Manager ≥ 2.17.0 and < 2.22.1 Vulnerable NIST National Vulnerability Database
F5 Nginx Open Source ≥ 1.30.0 and < 1.30.2≥ 1.31.0 and < 1.31.1≥ 0.1.17 and ≤ 0.9.7 Vulnerable CVE Program (cve.org) e CISA ADP
F5 Nginx Open Source ≥ 0.1.17 and ≤ 0.9.7≥ 1.0.0 and < 1.30.2version 1.31.0 Vulnerable NIST National Vulnerability Database
F5 Nginx Plus version r36-p1version r36-p4version r36-p3version r36-p2version r36version r32-p6version r32-p5version r32-p4
and 6 more version r32-p3version r32-p2version r32-p1version r32version 37.0.0.1≥ r33 and < r36
Vulnerable NIST National Vulnerability Database
F5 Nginx Plus ≥ R32 and < R32 P7≥ R36 and < R36 P5≥ 37.0 and < 37.0.1.1 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 ≤ 5.13.0 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.

ScoreVersionSeverityExpl.ImpactScored 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-122 · Heap-based Buffer Overflow

Other CVEs with this weakness →

EPSS over time FIRST

Oct 13, 2026 → Oct 14, 2026 · 2 reading(s) · max 2.70%

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 plus, f5/nginx open source
    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
  • Fix documented
    Oct 13, 2026 · NIST National Vulnerability Database
  • 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
    May 22, 2026 · f5

Source activity

Repeated readings are counted rather than listed.

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

References

15 on the record

Elsewhere on this site

Debian
every CVE for this vendor
Memory corruption
same class
CWE-122
other pages naming this weakness

Related CVEs (same products)

  • CVE-2026-110927 Openssh: openssh: a compressed payload can expand past the maximum packet size 11h
  • CVE-2026-110924 Openssh: openssh: gssapi delegated credentials can be stored after a failed authentication 11h
  • CVE-2026-110926 Openssh: openssh: shared lz77 compression dictionary leaks plaintext across channels 19h
  • CVE-2026-110923 Openssh: openssh: sftp can write outside the destination directory from a server-supplied path 19h
  • CVE-2026-110925 Openssh: openssh: '$' and '\' in a command-line username expand through %u 19h
  • CVE-2026-97205 NGINX ngx_http_core_module vulnerability 1d

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 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-2026-9256 is "NGINX ngx_http_rewrite_module vulnerability", rated High. It affects Debian Linux (Debian); 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 2.70% 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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