CriticalCVE-2026-9256

    NGINX ngx_http_rewrite_module vulnerability (CVE-2026-9256)

    Published Last modified Sources: BSI, Ubuntu, Red Hat, Debian LTS, Msrc Update Guide, F5, OSV, CVE.org, Debian, EUVD

    What is affected, what to do

    A flaw was found in the ngx_http_rewrite_module module of NGINX. When a rewrite directive uses a regex pattern with distinct, overlapping Perl-Compatible Regular Expression (PCRE) captures and a replacement string that references multiple such captures in a redirect or arguments context, an unauthenticated attacker can send crafted HTTP requests and cause a heap-based buffer overflow in the worker process, potentially allowing code execution or a denial of service by forcing the process to restart.

    An exploit is publicly available. Update F5 NGINX Plus to version 37.0.1.1, F5 NGINX Open Source to version 1.31.1, F5 NGINX Open Source to version 1.30.2.

    Affected
    • F5 NGINX Plus lt 37.0..37.0.1.1
    • F5 NGINX Plus gte R36..*
    • F5 NGINX Plus gte R32..*
    • F5 NGINX Open Source lt 1.31.0..1.31.1
    • F5 NGINX Open Source lt 1.30.0..1.30.2
    • F5 NGINX Open Source lte 0.1.17..0.9.7
    Fixed in
    • F5 NGINX Plus 37.0.1.1
    • F5 NGINX Open Source 1.31.1
    • F5 NGINX Open Source 1.30.2

    Not sure whether and how you are affected? Ask a question about this vulnerability

    Metrics

    9.2

    Priority

    XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.

    Source: NVD, CVSS v4

    8.1

    CVSS v3

    Severity High on the scale from 0 to 10.

    Source: BSI, Ubuntu, Red Hat, Debian LTS, Msrc Update Guide, F5, OSV, CVE.org, Debian, EUVD

    10.9 %

    EPSS score

    Elevated — model estimates 10-50% exploitation likelihood.

    Source: FIRST EPSS, percentile 95.8

    Show all metrics
    Severity
    Critical
    Priority (0–325)

    The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first?

    Read in glossary
    137.27 Methodology
    Exploit maturity

    An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack.

    Read in glossary
    PoC (publicly reported)
    XIEM Effective CVSS

    XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command.

    Read in glossary
    9.2 Methodology
    CVSS v3

    CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.

    Read in glossary
    8.1
    CVSS v4

    CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.

    Read in glossary
    9.2
    EPSS score

    The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“.

    Read in glossary
    10.9 %
    Elevated — model estimates 10-50% exploitation likelihood.
    EPSS percentile

    The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking.

    Read in glossary
    95.8
    Critical — this CVE ranks in the top fifth of all CVEs scored today (rank ≥ 80%).
    KEV status

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary
    —
    Published
    CISA assessment (SSVC)
    Exploitation: none known · not automatable · Technical impact: total
    Source: CISA Vulnrichment, as of 22 May 2026
    CWE

    CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect.

    Read in glossary
    CWE-122

    Detection rules

    No NEOSEC detection rule is available for this vulnerability yet.

    Classification under NIS2 and CRA

    Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

    NIS2

    NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.

    Read in glossary
    High technical severity: assess and remediate the vulnerability in vulnerability handling under Art. 21(2)(e) NIS2 and document the decision.
    CRA

    The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.

    Read in glossary
    From 11.12.2027, Annex I Part II CRA requires manufacturers of affected products with digital elements to handle vulnerabilities without delay and provide security updates.
    ISO/IEC 27001

    ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.

    Read in glossary
    Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

    Description

    A flaw was found in the ngx_http_rewrite_module module of NGINX. When a rewrite directive uses a regex pattern with distinct, overlapping Perl-Compatible Regular Expression (PCRE) captures and a replacement string that references multiple such captures in a redirect or arguments context, an unauthenticated attacker can send crafted HTTP requests and cause a heap-based buffer overflow in the worker process, potentially allowing code execution or a denial of service by forcing the process to restart.

    Source: BSI WID Portal, BSI CSAF, Ubuntu Security Notices, redhat_csaf, Debian LTS Advisories, Microsoft Security Update Guide, f5_askf5, OSV (Open Source Vulnerabilities), cvelistv5, NVD (NIST), Debian Security Advisories, ENISA EUVD, CVE.org (MITRE)

    Affected products

    The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.

    Affected products
    Affected versionsFixed in
    F5NGINX Open Source
    • 0.1.17 – ≤ 0.9.7
    • 1.30.0 – < 1.30.2
    • 1.31.0 – < 1.31.1
    • —
    • 1.30.2
    • 1.31.1
    F5NGINX Plus
    • ≥ R32
    • ≥ R36
    • 37.0 – < 37.0.1.1
    • —
    • —
    • 37.0.1.1
    f5dos
    • 4.9.0
    • 4.3.0 – ≤ 4.7.0
    • —
    • —
    f5nginx_gateway_fabric
    • 1.3.0 – ≤ 1.6.2
    • 2.0.0 – < 2.6.2
    • —
    • 2.6.2
    f5nginx_ingress_controller
    • 5.0.0 – < 5.4.3
    • 3.5.0 – ≤ 3.7.2
    • 4.0.0 – ≤ 4.0.1
    • 5.4.3
    • —
    • —
    f5nginx_instance_manager
    • 2.17.0 – < 2.22.1
    • 2.22.1
    f5nginx_open_source
    • 1.31.0
    • 0.1.17 – ≤ 0.9.7
    • 1.0.0 – < 1.30.2
    • —
    • —
    • 1.30.2
    f5nginx_plus
    • r32
    • 37.0.0.1
    • r36
    • r33 – < r36
    • —
    • —
    • —
    • r36
    f5waf
    • 5.9.0 – ≤ 5.13.0
    • 4.10.0 – ≤ 4.16.0
    • 5.2.0 – ≤ 5.8.0
    • —
    • —
    • —
    redhatdiscovery
    • —
    • —
    redhathardened_images
    • —
    • —
    redhatupdate_infrastructure
    • 5.0 – < 5.2
    • 5.2
    NGINXNGINX Open Source
    • < 1.30.2
    • < 1.31.1
    • 1.30.2
    • 1.31.1
    NGINXNGINX Plus
    • <R36 P5
    • <R32 P7
    • < 37.0.1.1
    • —
    • —
    • 37.0.1.1
    SplunkSOAR
    • < 8.6.0
    • 8.6.0
    Distribution and container packages (1)

    Downstream packages (e.g. Bitnami, Debian, Ubuntu, Red Hat). Versions refer to the distribution, not the vendor.

    Distribution and container packages
    Affected versionsFixed in
    bitnaminginx-gateway
    • 0.1.17
    • —

    Vendors and products

    Affected operating systems

    Affected operating systems
    Linuxdebiandebian_linux11.0
    Linuxredhatenterprise_linux10.0
    Linuxredhatenterprise_linux8.0
    Linuxredhatenterprise_linux9.0
    Linuxdebiannginxbookworm
    Linuxdebiannginxbullseye
    Linuxdebiannginxtrixie

    Weakness classes (CWE)

    • CWE-122Heap-based Buffer Overflow

      Variant

      A heap overflow condition is a buffer overflow, where the buffer that can be overwritten is allocated in the heap portion of memory, generally meaning that the buffer was allocated using a routine such as malloc().

      Entry at MITRE CWE-122

    Public exploit references

    Publicly reported proof-of-concepts, exploit modules and detection templates for this vulnerability. NEOSEC links to the original sources only and does not provide any exploit code.

    Public exploit references
    PoC-in-GitHub (nomi-sec)Nginx-chain-Rift-Poolslip (opens in a new tab)github.comPoC (publicly reported)reported, not verified
    PoC-in-GitHub (nomi-sec)CVE-2026-9256-POC (opens in a new tab)github.comPoC (publicly reported)reported, not verified
    PoC-in-GitHub (nomi-sec)CVE-2026-9256 (opens in a new tab)github.comPoC (publicly reported)reported, not verified

    References & sources

    Changes to this CVE

    Who changed this CVE and when: NVD (analysis, affected products, CVSS), the CVE publisher (CNA) and additional providers such as CISA (ADP).

    1. Record modifiedRed Hat ADP

      Show 2 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Referenceadded
      —
      https://access.redhat.com/errata/RHSA-2026:58981
      Affected versions (publisher)changed
      Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 8, Red Hat Enterprise Linux 9 (+8)
      Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 8, Red Hat Enterprise Linux 9 (+10)

      Source identifier: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c

    2. NVD analysis modifiedNVD

      Newly listed as affected:
      Product mapping changed:
      Show 16 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Product configurationadded
      —
      OR *cpe:2.3:a:f5:nginx_gateway_fabric:*:*:*:*:*:*:*:* versions from (including) 1.3.0 up to (including) 1.6.2 *cpe:2.3:a:f5:dos:*:*:*:*:*:nginx:*:* versions from (including) 4.3.0 up to (including) 4.7.0 *cpe:2.3:a:f5:dos:4.9.0:*:*:*:*:nginx:*:* *cpe:2.3:a:f5:waf:*:*:*:*:*:nginx:*:* versions from (including) 4.10.0 up to (including) 4.16.0 *cpe:2.3:a:f5:waf:*:*:*:*:*:nginx:*:* versions from (including) 5.2.0 up to (including) 5.8.0 *cpe:2.3:a:f5:nginx_ingress_controller:*:*:*:*:continuous_releases:*:*:* versions from (including) 3.5.0 up to (including) 3.7.2 *cpe:2.3:a:f5:nginx_instance_manager:*:*:*:*:*:*:*:* versions from (including) 2.17.0 up to (excluding) 2.22.1 *cpe:2.3:a:f5:waf:*:*:*:*:*:nginx:*:* versions from (including) 5.9.0 up to (including) 5.13.0 *cpe:2.3:a:f5:nginx_gateway_fabric:*:*:*:*:*:*:*:* versions from (including) 2.0.0 up to (excluding) 2.6.2 *cpe:2.3:a:f5:nginx_ingress_controller:*:*:*:*:continuous_releases:*:*:* versions from (including) 4.0.0 up to (including) 4.0.1 *cpe:2.3:a:f5:nginx_ingress_controller:*:*:*:*:continuous_releases:*:*:* versions from (including) 5.0.0 up to (excluding) 5.4.3
      Product configurationadded
      —
      OR *cpe:2.3:o:debian:debian_linux:11.0:*:*:*:*:*:*:* *cpe:2.3:o:redhat:enterprise_linux:8.0:*:*:*:*:*:*:* *cpe:2.3:a:redhat:discovery:-:*:*:*:*:*:*:* *cpe:2.3:o:redhat:enterprise_linux:9.0:*:*:*:*:*:*:* *cpe:2.3:o:redhat:enterprise_linux:10.0:*:*:*:*:*:*:* *cpe:2.3:a:redhat:hardened_images:-:*:*:*:*:*:*:* *cpe:2.3:a:redhat:update_infrastructure:*:*:*:*:*:*:*:* versions from (including) 5.0 up to (excluding) 5.2
      Product configurationchanged
      OR *cpe:2.3:a:f5:nginx_plus:*:*:*:*:*:*:*:* versions from (including) r32 up to (including) r36 *cpe:2.3:a:f5:nginx_open_source:*:*:*:*:*:*:*:* versions from (including) 0.1.17 up to (including) 0.9.7 *cpe:2.3:a:f5:nginx_open_source:*:*:*:*:*:*:*:* versions from (including) 1.0.0 up to (including) 1.30.1 *cpe:2.3:a:f5:nginx_open_source:1.31.0:*:*:*:*:*:*:* *cpe:2.3:a:f5:nginx_plus:*:*:*:*:*:*:*:* versions from (including) 37.0.0 up to (excluding) 37.0.1.1
      OR *cpe:2.3:a:f5:nginx_open_source:*:*:*:*:*:*:*:* versions from (including) 0.1.17 up to (including) 0.9.7 *cpe:2.3:a:f5:nginx_open_source:1.31.0:*:*:*:*:*:*:* *cpe:2.3:a:f5:nginx_plus:*:*:*:*:continuous_releases:*:*:* versions from (including) r33 up to (excluding) r36 *cpe:2.3:a:f5:nginx_plus:37.0.0.1:*:*:*:long-term_support:*:*:* *cpe:2.3:a:f5:nginx_plus:r32:-:*:*:continuous_releases:*:*:* *cpe:2.3:a:f5:nginx_plus:r32:p1:*:*:continuous_releases:*:*:* *cpe:2.3:a:f5:nginx_plus:r32:p2:*:*:continuous_releases:*:*:* *cpe:2.3:a:f5:nginx_plus:r32:p3:*:*:continuous_releases:*:*:* *cpe:2.3:a:f5:nginx_plus:r32:p4:*:*:continuous_releases:*:*:* *cpe:2.3:a:f5:nginx_plus:r32:p5:*:*:continuous_releases:*:*:* *cpe:2.3:a:f5:nginx_plus:r32:p6:*:*:continuous_releases:*:*:* *cpe:2.3:a:f5:nginx_plus:r36:-:*:*:continuous_releases:*:*:* *cpe:2.3:a:f5:nginx_plus:r36:p1:*:*:continuous_releases:*:*:* *cpe:2.3:a:f5:nginx_plus:r36:p2:*:*:continuous_releases:*:*:* *cpe:2.3:a:f5:nginx_plus:r36:p3:*:*:continuous_releases:*:*:* *cpe:2.3:a:f5:nginx_plus:r36:p4:*:*:continuous_releases:*:*:* *cpe:2.3:a:f5:nginx_open_source:*:*:*:*:*:*:*:* versions from (including) 1.0.0 up to (excluding) 1.30.2
      Reference typechanged
      CVE: http://www.openwall.com/lists/oss-security/2026/05/22/14 Types: Mailing List, Third Party Advisory
      CVE: http://www.openwall.com/lists/oss-security/2026/05/22/14 Types: Mailing List
      Reference typeadded
      —
      CVE: https://lists.debian.org/debian-lts-announce/2026/06/msg00023.html Types: Mailing List, Third Party Advisory
      Reference typeadded
      —
      redhat-SADP: https://access.redhat.com/errata/RHSA-2026:20351 Types: Third Party Advisory
      Reference typeadded
      —
      redhat-SADP: https://access.redhat.com/errata/RHSA-2026:28212 Types: Third Party Advisory
      Reference typeadded
      —
      redhat-SADP: https://access.redhat.com/errata/RHSA-2026:28921 Types: Third Party Advisory
      Reference typeadded
      —
      redhat-SADP: https://access.redhat.com/errata/RHSA-2026:28973 Types: Third Party Advisory
      Reference typeadded
      —
      redhat-SADP: https://access.redhat.com/errata/RHSA-2026:29151 Types: Third Party Advisory
      Reference typeadded
      —
      redhat-SADP: https://access.redhat.com/errata/RHSA-2026:29874 Types: Third Party Advisory
      Reference typeadded
      —
      redhat-SADP: https://access.redhat.com/errata/RHSA-2026:33313 Types: Third Party Advisory
      Reference typeadded
      —
      redhat-SADP: https://access.redhat.com/errata/RHSA-2026:44481 Types: Third Party Advisory
      Reference typeadded
      —
      redhat-SADP: https://access.redhat.com/security/cve/CVE-2026-9256 Types: Third Party Advisory
      Reference typeadded
      —
      redhat-SADP: https://bugzilla.redhat.com/show_bug.cgi?id=2480746 Types: Issue Tracking, Third Party Advisory
      Reference typeadded
      —
      redhat-SADP: https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-9256.json Types: Third Party Advisory

      Source identifier: nvd@nist.gov

    3. Record modifiedRed Hat ADP

      Show 2 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Referenceadded
      —
      https://access.redhat.com/errata/RHSA-2026:44481
      Affected versions (publisher)changed
      Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 8, Red Hat Enterprise Linux 9 (+5)
      Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 8, Red Hat Enterprise Linux 9 (+8)

      Source identifier: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c

    4. Initial analysis by NVDNVD

      Newly listed as affected:
      Show 3 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Product configurationadded
      —
      OR *cpe:2.3:a:f5:nginx_plus:*:*:*:*:*:*:*:* versions from (including) r32 up to (including) r36 *cpe:2.3:a:f5:nginx_open_source:*:*:*:*:*:*:*:* versions from (including) 0.1.17 up to (including) 0.9.7 *cpe:2.3:a:f5:nginx_open_source:*:*:*:*:*:*:*:* versions from (including) 1.0.0 up to (including) 1.30.1 *cpe:2.3:a:f5:nginx_open_source:1.31.0:*:*:*:*:*:*:* *cpe:2.3:a:f5:nginx_plus:*:*:*:*:*:*:*:* versions from (including) 37.0.0 up to (excluding) 37.0.1.1
      Reference typeadded
      —
      CVE: http://www.openwall.com/lists/oss-security/2026/05/22/14 Types: Mailing List, Third Party Advisory
      Reference typeadded
      —
      F5 Networks: https://my.f5.com/manage/s/article/K000161377 Types: Mitigation, Vendor Advisory

      Source identifier: nvd@nist.gov

    One NVD translation into another language is hidden.

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