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Full vulnerability report · 2026
CVE-2026-9256High confidence

NGINX ngx_http_rewrite_module vulnerability

F5 · NGINX Plus

Official source article: F5 K000161377 ↗. Check the applicable product and release in the original source.

9.2CriticalCVSS 4.0
Recommended action
Within 72 hours

Critical technical impact with a remotely reachable, unauthenticated path; no CISA KEV confirmation is currently recorded.

Patch available
R
Operational reassessment

Published severity in operational context

Open reassessment dashboard →
Published severityCriticalOperational priority:Critical, unchanged from published severity.unchanged

Evidence used

  • No CISA KEV confirmation is currently recorded.
  • The selected CVSS metric records a network-reachable, unauthenticated path with no user interaction.
  • EPSS is 2.70% for the current model date.

Compensating controls

  • Validate the affected product branch and deploy the verified fixed release.
  • Restrict the affected network interface to trusted sources where business-safe.
  • Monitor vendor guidance and exploitation sources for a material change.

Verification

  1. Confirm that the asset runs F5 NGINX Plus and falls inside the recorded affected range.
  2. Verify the installed build against the product-specific fixed version after deployment.
  3. Validate exposure, authentication requirements and compensating controls in the actual environment.
  4. Reopen this reassessment when CVSS, KEV, EPSS, exploit evidence or remediation changes.
Mitigation target: Within 3 daysRemediation target: Within 90 days

This automated reassessment organises public evidence. It does not know asset exposure, business impact or control effectiveness and does not replace CVSS or a human risk decision.

Distribution package intelligence

Release-specific package status

Alpine, Debian, ubuntu findings are scoped to the named distribution, release and source package. An absent finding does not mean a package is unaffected.

8 package states
Repository candidate not checked

A published vendor fix does not prove that a matching update is enabled and installable on a particular asset. Confirm the local package candidate before scheduling remediation.

Distribution releaseSource packageVendor stateFixed versionEvidence
Alpine v3.23v3.23 · mainnginxVendor fix publishedAlpine records a security fix at this version. An absent entry does not mean the package is unaffected.1.28.3-r2Alpine Security Database ↗Source updated 3 Oct 2026
Alpine v3.22v3.22 · mainnginxVendor fix publishedAlpine records a security fix at this version. An absent entry does not mean the package is unaffected.1.28.3-r2Alpine Security Database ↗Source updated 3 Oct 2026
Alpine v3.21v3.21 · mainnginxVendor fix publishedAlpine records a security fix at this version. An absent entry does not mean the package is unaffected.1.26.3-r1Alpine Security Database ↗Source updated 3 Oct 2026
Debian trixietrixie · sourcenginxVendor fix publishedDebian records a fixed source-package version for this release.1.26.3-3+deb13u6Debian Security Tracker ↗Source updated 6 Oct 2026
Debian bookwormbookworm · sourcenginxVendor fix publishedDebian records a fixed source-package version for this release.1.22.1-9+deb12u8Debian Security Tracker ↗Source updated 6 Oct 2026
Debian forkyforky · sourcenginxVendor fix publishedDebian records a fixed source-package version for this release.1.30.1-3Debian Security Tracker ↗Source updated 6 Oct 2026
Debian sidsid · sourcenginxVendor fix publishedDebian records a fixed source-package version for this release.1.30.1-3Debian Security Tracker ↗Source updated 6 Oct 2026
Ubuntu 24.04 LTSnoble · standard archivenginxVendor fix publishedCanonical reports that a fixed source package version has been published. Repository candidate availability is not checked by BlackTree.1.24.0-2ubuntu7.9Canonical Ubuntu Security ↗Source updated 5 Oct 2026
Direct vendor intelligence

Authoritative vendor CSAF and VEX advisories

Structured product status and remediation from the issuing vendor. Product-state explanations are always visible; large lists can be searched or downloaded.

1 current
CVE-2026-9256 · CSAF 2.0 · revision 3 · finalRed Hat Product Securitynginx: ngx_http_rewrite_module: code execution and denial of service
1 known affected

The vendor explicitly identifies these products as affected by this CVE.

  • insights-proxy/insights-proxy-container-rhel9 as a component of Red Hat Lightspeed proxy 1
Summary
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.
Remediation
For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258
Optional official sources

National CERT insights
?CERT means Computer Emergency Response Team; CSIRT is the closely related term Computer Security Incident Response Team.

Choose official national sources for this report. Each advisory shows its original language. Your selection is remembered on this device and included in shared links.

Official European source

ENISA European Vulnerability Database

Official EUVD identifiers, advisory evidence and known-exploited context. Missing fields are not treated as evidence of low risk.

1 current
ENISA EUVD identifier

EUVD-2026-31444

No EUVD known-exploited evidence

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.

EUVD state
Present in the current official mapping
Known exploitation
Not present in the current ENISA EUVD known-exploited dataset. This is not proof of no exploitation.
ENISA score
9.2 · CVSS 4.0
Advisory evidence
No linked advisory details stored yet
Recommended actionWithin 72 hours

Critical technical impact with a remotely reachable, unauthenticated path; no CISA KEV confirmation is currently recorded.

Patch available
01

What, why and how

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.

What

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.

Why

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().

How

An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may execute code or commands in the affected security context.

What

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.

Why

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().

How

An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may execute code or commands in the affected security context.

02

Exploit reality and attack path

CVSS severity, EPSS forecast probability, public exploit material and CISA-confirmed exploitation are separate signals.

Observed exploitation
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
No confirmed evidence

No CISA KEV match was present at the last successful refresh. This means no confirmation from that source, not proof of no exploitation.

Public PoC / exploit material
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
None recorded

No exploit-tagged reference or CISA SSVC proof-of-concept state is currently recorded. Research may still exist outside the structured feeds.

Likely attack path
a network path → Heap-based Buffer Overflow → execute code or commands in the affected security context
Attack surface
Network
Privileges required
None: unauthenticated exploitation is possible
User interaction
None
Attack complexity
High: exploitation depends on specific conditions
Security boundary
Not a CVSS 4.0 base metric
Weakness
?CWE means Common Weakness Enumeration: a standard category for the underlying weakness.
CWE-122 ↗

CWE-122: Heap-based Buffer Overflow. 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().

CVSS vector
?CVSS means Common Vulnerability Scoring System. The vector records the metric values used to calculate technical severity.
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

Common Vulnerability Scoring System 4.0: the compact vector below is decoded into plain language.

AVNetworkAttack vector: The vulnerable component can be reached over a network.ACHighAttack complexity: Successful exploitation depends on specific conditions outside the attacker's direct control.ATPresentAttack requirements: A particular deployment or execution condition must be present.PRNonePrivileges required: The attacker does not need an account or existing privileges.UINoneUser interaction: No action by another user is required.VCHighVulnerable-system confidentiality: A successful attack can cause a major loss.VIHighVulnerable-system integrity: A successful attack can cause a major loss.VAHighVulnerable-system availability: A successful attack can cause a major loss.SCNoneSubsequent-system confidentiality: No direct loss is represented by this metric.SINoneSubsequent-system integrity: No direct loss is represented by this metric.SANoneSubsequent-system availability: No direct loss is represented by this metric.
Post-exploitation / living off the land
After compromise, an attacker may use built-in shells, scripting engines, scheduled tasks and native network utilities for discovery, persistence or movement. This is a plausible LoTL path, not evidence that it has occurred for every attack.
NetworkUnauthenticatedRemote code executionCWE-122
A

Official authority intelligence

Only matched European and national findings are included. Language selectors and unavailable sources are omitted.

ENISA EUVD · EUVD-2026-31444Official EUVD mapping

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.

Official EUVD record ↗
BSI · German · WID-SEC-2026-2933Splunk SOAR: Mehrere Schwachstellen

Ein Angreifer kann mehrere Schwachstellen in Splunk SOAR ausnutzen, um Sicherheitsvorkehrungen zu umgehen, um Informationen offenzulegen, um Dateien zu manipulieren, um einen SQL-Injection Angriff durchzuführen, um einen Cross-Site Scripting Angriff durchzuführen, und um beliebigen Programmcode auszuführen.

Official advisory ↗
BSI · German · WID-SEC-2026-2437Oracle Communications: Mehrere Schwachstellen

Ein entfernter, anonymer oder authentisierter Angreifer kann mehrere Schwachstellen in Oracle Communications ausnutzen, um die Vertraulichkeit, Integrität und Verfügbarkeit zu gefährden.

Official advisory ↗
BSI · German · WID-SEC-2026-1661NGINX Open Source und NGINX Plus: Schwachstelle ermöglicht Denial of Service und potenziell Codeausführung

Ein entfernter, anonymer Angreifer kann eine Schwachstelle in NGINX und NGINX NGINX Plus ausnutzen, um einen Denial of Service Angriff durchzuführen, und potenziell um beliebigen Programmcode auszuführen.

Official advisory ↗
Canadian Centre for Cyber Security · English · AV26-508cPanel security advisory (AV26-508)

The Cyber Centre encourages users and administrators to review the provided web links and apply the necessary updates.

Official advisory ↗
Canadian Centre for Cyber Security · English · AV26-501F5 security advisory (AV26-501)

On May 22, 2026, F5 published a security advisory to address a critical vulnerability in the following products:

Official advisory ↗
CERT-FR · French · CERTFR-2026-AVI-1056Multiples vulnérabilités dans les produits Splunk

ord?id=CVE-2026-76398 Référence CVE CVE-2026-76399 https://www.cve.org/CVERecord?id=CVE-2026-76399 Référence CVE CVE-2026-76400 https://www.cve.org/CVERecord?id=CVE-2026-76400 Référence CVE CVE-2026-76401 https://www.cve.org/CVERecord?id=CVE-2026-76401 Référence CVE CVE-2026-76402 https://www.cve.org/CVERecord?id=CVE-2026-76402 Référence CVE CVE-2026-76403 https://www.cve.org/CVERecord?id=CVE-2026-76403 Référence CVE CVE-2026-76404 https://www.cve.org/CVERecord?id=CVE-2026-76404 Référence CVE CVE-2026-76405 https://www.cve.org/CVERecord?id=CVE-2026-76405 Référence CVE CVE-2026-9076 https://www.cve.org/CVERecord?id=CVE-2026-9076 Référence CVE CVE-2026-9256 https://www.cve.org/CVERecord?id=CVE-2026-9256 Gestion détaillée du document le 20 août 2026 Version initiale Alertes Avis Bulletins d’actualités Mentions légales Conditions générales À propos Contact cyber.gouv.fr service-public.fr legifrance.gouv.fr info.gouv.fr france.fr info.gouv.fr/risques Premier Ministre / Secrétariat Général de la Défense et de la Sécurité Nationale / Agence nationale de la sécurité des systèmes d'information

Official advisory ↗
CERT-FR · French · CERTFR-2026-AVI-0643Vulnérabilité dans Nginx

Une vulnérabilité a été découverte dans Nginx. Elle permet à un attaquant de provoquer une exécution de code arbitraire à distance et un déni de service à distance.

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2026-019996F5 Networksのnginx open source等の複数製品におけるヒープベースのバッファオーバーフローの脆弱性

NGINX PlusおよびNGINXオープンソースには、ngx_http_rewrite_moduleモジュールに脆弱性があります。この脆弱性は、rewriteディレクティブが異なるが重複するPerl互換正規表現（PCRE）キャプチャ（例：^/((.*))$）を含む正規表現パターンと、複数のそのようなキャプチャを参照する置換文字列（例：$1$2）をリダイレクトまたは引数コンテキストで使用する場合に存在します。認証されていない攻撃者は、自身の制御を超えた条件とともに細工されたHTTPリクエストを送信することで、この脆弱性を悪用できます。これにより、NGINXワーカープロセスでヒープバッファオーバーフローが発生し、プロセスが再起動される可能性があります。さらに、ASLR（アドレス空間配置のランダム化）が無効化されているシステムや攻撃者がASLRを回避できる場合、攻撃者はコードを実行できます。なお、技術サポート終了（EoTS）を迎えたソフトウェアバージョンについては評価されていません。

Official advisory ↗
03

Patch and workaround

Operational remediation based on structured source evidence.

Status
?Patch availability is based on structured fixed-version fields and authoritative update references. If no fix is verified, check the vendor advisory before making a change.
Patch available
Affected
insights-proxy/insights-proxy-container-rhel9 as a component of Red Hat Lightspeed proxy 1
Fixed
Action
For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258
Workaround
No verified workaround is recorded. If business-safe, reduce exposure to the affected interface and allow only trusted sources until authoritative guidance is available.
04

Evidence and provenance

Published 22 May 2026 · Last source change 25 Aug 2026, 12:05 UTC · CWE-122 · Heap-based Buffer Overflow

CVE recordCVE.org · 5.2
CVSS sourceCNA
EPSS source
?The date BlackTree first stored a score for this CVE from the daily FIRST EPSS feed.
FIRST · tracked since 2026-08-14
European sourceENISA EUVD · EUVD-2026-31444
Product sourceVendor CSAF · Red Hat Product Security
Remediation sourceVendor CSAF · Red Hat Product Security
CWE sourceCNA
NVD statusNVD modified after enrichment

Core structured fields are present and their contributing authorities are shown above.

Material change intelligence

What changed after publication

View recent updates ↗
  1. Vendor guidanceAuthoritative vendor guidance changed: removed vendor advisory: access.redhat.com/RHSA-2026:58981.
    Before
    mitigation: my.f5.com/K000161377 · remediation: my.f5.com/K000161377 · vendor advisory: access.redhat.com/RHSA-2026:58981
    After
    mitigation: my.f5.com/K000161377 · remediation: my.f5.com/K000161377
    f5sirt@f5.com ↗
  2. Vendor guidanceAuthoritative vendor guidance changed: added vendor advisory: access.redhat.com/RHSA-2026:58981.
    Before
    mitigation: my.f5.com/K000161377 · remediation: my.f5.com/K000161377
    After
    mitigation: my.f5.com/K000161377 · remediation: my.f5.com/K000161377 · vendor advisory: access.redhat.com/RHSA-2026:58981
    f5sirt@f5.com ↗
  3. Affected versionsThe structured affected or fixed version information changed.
    Before
    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 · Fixed: No fixed version is explicitly recorded in the structured CVE data.
    After
    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 · Fixed: For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258
    Red Hat Product Security ↗
  4. Remediation statusRemediation status changed from Mitigation available to Patch available.
    Before
    Mitigation available
    After
    Patch available
    Red Hat Product Security ↗
Material fields only · duplicate refreshes suppressed · history retained for the configured operational retention period
CVE published
Mitigation reference recorded
Fixed release recorded from official guidance
ENISA EUVD · EUVD-2026-31444↗Red Hat Product Security security advisory↗CVE authority or vendor reference · F5 K000161377↗Official CVE record (CNA and ADP data)↗NVD record↗
Technical terms and abbreviations used in this report
CVE
Common Vulnerabilities and Exposures: the public identifier for one disclosed vulnerability.
CVSS
Common Vulnerability Scoring System: a technical severity framework; it is not patching priority by itself.
EPSS
Exploit Prediction Scoring System: FIRST's estimate of the probability that exploitation activity will be observed in the next 30 days; it is a forecast, not confirmation.
CWE
Common Weakness Enumeration: the standard category describing the underlying software or hardware weakness.
CNA
CVE Numbering Authority: an organisation authorised to assign and publish CVE records.
CISA ADP
Cybersecurity and Infrastructure Security Agency Authorized Data Publisher: structured enrichment added to a CVE record.
NVD
National Vulnerability Database: NIST's enrichment service for CVE records.
CERT / CSIRT
A computer security incident response team that publishes warnings or coordinates incident response.
PoC
Proof of concept: public material that demonstrates or helps reproduce exploitation.
CSAF
Common Security Advisory Framework: a machine-readable format for security advisories.
LoTL
Living off the land: abuse of legitimate tools or system functions during an attack.
Free version - for non-commercial use only.CVE-2026-9256 · cve.blacktree.nl