CVE-2026-9256

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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$2) in a redirect or arguments context. An unauthenticated attacker along with conditions beyond their control can exploit this vulnerability by sending crafted HTTP requests. This may cause a heap buffer overflow in the NGINX worker process leading to a restart. Additionally, attackers can execute code on systems with Address Space Layout Randomization (ASLR) disabled or when the attacker can bypass ASLR. \n\n\nNote: Software versions which have reached End of Technical Support (EoTS) are not evaluated."}, {"lang": "es", "value": "NGINX Plus y NGINX Open Source tienen una vulnerabilidad en el m\u00f3dulo ngx_http_rewrite_module. Esta vulnerabilidad existe cuando una directiva de reescritura utiliza un patr\u00f3n de expresi\u00f3n regular (regex) con capturas de expresiones regulares compatibles con Perl (PCRE) distintas y superpuestas (por ejemplo, ^/((.*))$) y una cadena de reemplazo que hace referencia a m\u00faltiples de dichas capturas (por ejemplo, $1$2) en un contexto de redirecci\u00f3n o de argumentos. Un atacante no autenticado, junto con condiciones fuera de su control, puede explotar esta vulnerabilidad enviando solicitudes HTTP manipuladas. Esto puede causar un desbordamiento de b\u00fafer de pila en el proceso de trabajador de NGINX, lo que lleva a un reinicio. Adem\u00e1s, los atacantes pueden ejecutar c\u00f3digo en sistemas con la aleatorizaci\u00f3n del espacio de direcciones (ASLR) deshabilitada o cuando el atacante puede eludir ASLR.\n\nNota: Las versiones de software que han alcanzado el fin del soporte t\u00e9cnico (EoTS) no se eval\u00faan."}], "id": "CVE-2026-9256", "lastModified": "2026-08-25T13:19:33.400", "metrics": {"cvssMetricV31": [{"cvssData": {"attackComplexity": "HIGH", "attackVector": "NETWORK", "availabilityImpact": "HIGH", "baseScore": 8.1, "baseSeverity": "HIGH", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "privilegesRequired": "NONE", "scope": "UNCHANGED", "userInteraction": "NONE", "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H", "version": "3.1"}, "exploitabilityScore": 2.2, "impactScore": 5.9, "source": "f5sirt@f5.com", "type": "Secondary"}, {"cvssData": {"attackComplexity": "HIGH", "attackVector": "NETWORK", "availabilityImpact": "HIGH", "baseScore": 8.1, "baseSeverity": "HIGH", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "privilegesRequired": "NONE", "scope": "UNCHANGED", "userInteraction": "NONE", "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H", "version": "3.1"}, "exploitabilityScore": 2.2, "impactScore": 5.9, "source": "0b0ca135-0b70-47e7-9f44-1890c2a1c46c", "type": "Secondary"}], "cvssMetricV40": [{"cvssData": {"Automatable": "NOT_DEFINED", "Recovery": "NOT_DEFINED", "Safety": "NOT_DEFINED", "attackComplexity": "HIGH", "attackRequirements": "PRESENT", "attackVector": "NETWORK", "availabilityRequirement": "NOT_DEFINED", "baseScore": 9.2, "baseSeverity": "CRITICAL", "confidentialityRequirement": "NOT_DEFINED", "exploitMaturity": "NOT_DEFINED", "integrityRequirement": "NOT_DEFINED", "modifiedAttackComplexity": "NOT_DEFINED", "modifiedAttackRequirements": "NOT_DEFINED", "modifiedAttackVector": "NOT_DEFINED", "modifiedPrivilegesRequired": "NOT_DEFINED", "modifiedSubAvailabilityImpact": "NOT_DEFINED", "modifiedSubConfidentialityImpact": "NOT_DEFINED", "modifiedSubIntegrityImpact": "NOT_DEFINED", "modifiedUserInteraction": "NOT_DEFINED", "modifiedVulnAvailabilityImpact": "NOT_DEFINED", "modifiedVulnConfidentialityImpact": "NOT_DEFINED", "modifiedVulnIntegrityImpact": "NOT_DEFINED", "privilegesRequired": "NONE", "providerUrgency": "NOT_DEFINED", "subAvailabilityImpact": "NONE", "subConfidentialityImpact": "NONE", "subIntegrityImpact": "NONE", "userInteraction": "NONE", "valueDensity": "NOT_DEFINED", "vectorString": "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", "version": "4.0", "vulnAvailabilityImpact": "HIGH", "vulnConfidentialityImpact": "HIGH", "vulnIntegrityImpact": "HIGH", "vulnerabilityResponseEffort": "NOT_DEFINED"}, "source": "f5sirt@f5.com", "type": "Secondary"}], "ssvcV203": [{"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "ssvcData": {"id": "CVE-2026-9256", "options": [{"exploitation": "none"}, {"automatable": "no"}, {"technicalImpact": "total"}], "role": "CISA Coordinator", "timestamp": "2026-05-22T00:00:00+00:00", "version": "2.0.3"}}]}, "published": "2026-05-22T15:16:27.073", "references": [{"source": "f5sirt@f5.com", "tags": ["Mitigation", "Vendor Advisory"], "url": "https://my.f5.com/manage/s/article/K000161377"}, {"source": "af854a3a-2127-422b-91ae-364da2661108", "tags": ["Mailing List"], "url": "http://www.openwall.com/lists/oss-security/2026/05/22/14"}, {"source": "af854a3a-2127-422b-91ae-364da2661108", "tags": ["Mailing List", "Third Party Advisory"], "url": "https://lists.debian.org/debian-lts-announce/2026/06/msg00023.html"}, {"source": "0b0ca135-0b70-47e7-9f44-1890c2a1c46c", "tags": ["Third Party Advisory"], "url": "https://access.redhat.com/errata/RHSA-2026:20351"}, {"source": "0b0ca135-0b70-47e7-9f44-1890c2a1c46c", "tags": ["Third Party Advisory"], "url": "https://access.redhat.com/errata/RHSA-2026:28212"}, {"source": "0b0ca135-0b70-47e7-9f44-1890c2a1c46c", "tags": ["Third Party Advisory"], "url": "https://access.redhat.com/errata/RHSA-2026:28921"}, {"source": "0b0ca135-0b70-47e7-9f44-1890c2a1c46c", "tags": ["Third Party Advisory"], "url": "https://access.redhat.com/errata/RHSA-2026:28973"}, {"source": "0b0ca135-0b70-47e7-9f44-1890c2a1c46c", "tags": ["Third Party Advisory"], "url": "https://access.redhat.com/errata/RHSA-2026:29151"}, {"source": "0b0ca135-0b70-47e7-9f44-1890c2a1c46c", "tags": ["Third Party Advisory"], "url": "https://access.redhat.com/errata/RHSA-2026:29874"}, {"source": "0b0ca135-0b70-47e7-9f44-1890c2a1c46c", "tags": ["Third Party Advisory"], "url": "https://access.redhat.com/errata/RHSA-2026:33313"}, {"source": "0b0ca135-0b70-47e7-9f44-1890c2a1c46c", "tags": ["Third Party Advisory"], "url": "https://access.redhat.com/errata/RHSA-2026:44481"}, {"source": "0b0ca135-0b70-47e7-9f44-1890c2a1c46c", "url": "https://access.redhat.com/errata/RHSA-2026:58981"}, {"source": "0b0ca135-0b70-47e7-9f44-1890c2a1c46c", "tags": ["Third Party Advisory"], "url": "https://access.redhat.com/security/cve/CVE-2026-9256"}, {"source": "0b0ca135-0b70-47e7-9f44-1890c2a1c46c", "tags": ["Issue Tracking", "Third Party Advisory"], "url": "https://bugzilla.redhat.com/show_bug.cgi?id=2480746"}, {"source": "0b0ca135-0b70-47e7-9f44-1890c2a1c46c", "tags": ["Third Party Advisory"], "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-9256.json"}], "sourceIdentifier": "f5sirt@f5.com", "vulnStatus": "Modified", "weaknesses": [{"description": [{"lang": "en", "value": "CWE-122"}], "source": "f5sirt@f5.com", "type": "Secondary"}, {"description": [{"lang": "en", "value": "CWE-122"}], "source": "0b0ca135-0b70-47e7-9f44-1890c2a1c46c", "type": "Secondary"}]}

{"bugzilla": {"description": "nginx: ngx_http_rewrite_module: code execution and denial of service", "id": "2480746", "url": "https://bugzilla.redhat.com/show_bug.cgi?id=2480746"}, "csaw": false, "cvss3": {"cvss3_base_score": "8.1", "cvss3_scoring_vector": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H", "status": "draft"}, "cwe": "CWE-122", "details": ["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."], "mitigation": {"lang": "en:us", "value": "To mitigate this vulnerability, use named captures instead of unnamed captures in rewrite definitions.\nFor example, the following rewrite directive uses unnamed PCRE capture groups, $1 and $2:\n~~~\nrewrite ^/users/([0-9]+)/profile/(.*)$ /profile.php?id=$1&tab=$2 last;\n~~~\nTo mitigate this vulnerability for this example, replace $1 and $2 with the appropriate named captures, $user_id and $section:\n~~~\nrewrite ^/users/(?<user_id>[0-9]+)/profile/(?<section>.*)$ /profile.php?id=$user_id&tab=$section last;\n~~~"}, "name": "CVE-2026-9256", "package_state": [{"cpe": "cpe:/o:redhat:enterprise_linux:10", "fix_state": "Affected", "package_name": "nginx", "product_name": "Red Hat Enterprise Linux 10"}, {"cpe": "cpe:/o:redhat:enterprise_linux:8", "fix_state": "Affected", "package_name": "nginx:1.24/nginx", "product_name": "Red Hat Enterprise Linux 8"}, {"cpe": "cpe:/o:redhat:enterprise_linux:9", "fix_state": "Affected", "package_name": "nginx", "product_name": "Red Hat Enterprise Linux 9"}, {"cpe": "cpe:/o:redhat:enterprise_linux:9", "fix_state": "Affected", "package_name": "nginx:1.24/nginx", "product_name": "Red Hat Enterprise Linux 9"}, {"cpe": "cpe:/o:redhat:enterprise_linux:9", "fix_state": "Affected", "package_name": "nginx:1.26/nginx", "product_name": "Red Hat Enterprise Linux 9"}, {"cpe": "cpe:/a:redhat:hummingbird:1", "fix_state": "Affected", "package_name": "nginx", "product_name": "Red Hat Hardened Images"}, {"cpe": "cpe:/a:redhat:insights_proxy:1", "fix_state": "Affected", "package_name": "insights-proxy/insights-proxy-container-rhel9", "product_name": "Red Hat Lightspeed proxy 1"}], "public_date": "2026-05-22T14:11:41Z", "references": ["https://www.cve.org/CVERecord?id=CVE-2026-9256\nhttps://nvd.nist.gov/vuln/detail/CVE-2026-9256\nhttps://my.f5.com/manage/s/article/K000161377"], "statement": "To exploit this vulnerability, a rewrite directive must be configured with a regex pattern that uses distinct, overlapping PCRE captures and a replacement string referencing multiple such captures, limiting its exposure as this is not the default configuration. This issue allows an attacker to potentially execute arbitrary code or cause a denial of service by forcing the worker process to restart.\nDefault Red Hat Enterprise Linux security features, including SELinux enforcement, Address Space Layout Randomization (ASLR) and NX (No-Execute) stack protection, significantly increase the difficulty of achieving arbitrary code execution, limiting the impact of this vulnerability.\nDue to these reasons, this flaw has been rated with an important severity.", "threat_severity": "Important"}

{"affected": [{"configurations": [{"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "[1.31.0,1.31.1)"}}, {"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "[1.30.0,1.30.2)"}}, {"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "[0.1.17,*]"}}], "enrichment": {"confidence": 100.0, "confidence_source": "matching", "scores": [{"score": 100.0, "source": "matching"}]}, "original": {"product": "NGINX Open Source", "source": "cna", "vendor": "F5"}, "product": "nginx_open_source", "vendor": "f5"}, {"configurations": [{"platform": null, "status": "affected", "versions": {"scheme": "generic", "value": "[37.0,37.0.1.1)"}}, {"platform": null, "status": "affected", "versions": {"scheme": "generic", "value": "[R36,R36 P5)"}}, {"platform": null, "status": "affected", "versions": {"scheme": "generic", "value": "[R32,R32 P7)"}}], "enrichment": {"confidence": 100.0, "confidence_source": "matching", "scores": [{"score": 100.0, "source": "matching"}]}, "original": {"product": "NGINX Plus", "source": "cna", "vendor": "F5"}, "product": "nginx_plus", "vendor": "f5"}], "created": "2026-05-22T15:30:38.637679+00:00", "updated": "2026-10-25T20:30:14.767854+00:00", "vendors": ["f5", "f5$PRODUCT$nginx_open_source", "f5$PRODUCT$nginx_plus"]}