ESB-2026.5161

=========================================================================== AUSCERT External Security Bulletin Redistribution ESB-2026.5161 K000161028: NGINX ngx_http_charset_module vulnerability CVE-2026-42934 14 May 2026 =========================================================================== AUSCERT Security Bulletin Summary --------------------------------- Product: F5 DoS for NGINX F5 NGINX App Protect WAF F5 WAF for NGINX NGINX App Protect DoS NGINX Gateway Fabric NGINX Ingress Controller NGINX Instance Manager NGINX Open Source NGINX Plus Publisher: F5 Networks Operating System: F5 Resolution: Patch/Upgrade CVE Names: CVE-2026-42934 Original Bulletin: https://my.f5.com/manage/s/article/K000161028 Comment: CVSS (Max): 4.8 CVE-2026-42934 (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:L) CVSS Source: F5 Networks Calculator: https://www.first.org/cvss/calculator/3.1#CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:L EPSS (Max): None available when published - --------------------------BEGIN INCLUDED TEXT-------------------- K000161028: NGINX ngx_http_charset_module vulnerability CVE-2026-42934 Published Date: May 13, 2026 Security Advisory Description NGINX Plus and NGINX Open Source have a vulnerability in the ngx_http_charset_module module. When charset, source_charset, and charset_map and proxy_pass with disabled buffering ("off") directives are configured, unauthenticated attackers can send requests that with conditions beyond the attackers' control to cause a heap buffer over-read in the NGINX worker process, leading to limited disclosure of memory or a restart. (CVE-2026-42934) Impact This vulnerability may allow remote attackers to have limited control to disclose memory contents or restart the NGINX worker process. There is no control plane exposure; this is a data plane issue only. Security Advisory Status F5 Product Development has assigned ID 151 (NGINX) to this vulnerability. This issue has been classified as CWE-125: Out-of-bounds Read. To determine if your product and version have been evaluated for this vulnerability, refer to the Evaluated products box. To determine if your release is known to be vulnerable, the components or features that are affected by the vulnerability, and for information about releases, point releases, or hotfixes that address the vulnerability, refer to the following tables. For more information about security advisory versioning, refer to K51812227: Understanding security advisory versioning. In this section o BIG-IP Next o BIG-IP and BIG-IQ o F5 Distributed Cloud and NGINX Services o F5OS o NGINX o Other products BIG-IP Next +-------------+------+-----------------+----------+----------+----------------+ | | |Versions known to|Fixes |Severity/ |Vulnerable | |Product |Branch|be vulnerable^1 |introduced|CVSS score|component or | | | | |in | |feature | +-------------+------+-----------------+----------+----------+----------------+ |BIG-IP Next |All |None |Not |Not |None | |SPK | | |applicable|vulnerable| | +-------------+------+-----------------+----------+----------+----------------+ |BIG-IP Next |All |None |Not |Not |None | |CNF | | |applicable|vulnerable| | +-------------+------+-----------------+----------+----------+----------------+ |BIG-IP Next | | |Not |Not | | |for |All |None |applicable|vulnerable|None | |Kubernetes | | | | | | +-------------+------+-----------------+----------+----------+----------------+ ^1F5 evaluates only software versions that have not yet reached the End of Technical Support (EoTS) phase of their lifecycle. For more information, refer to the Security hotfixes section of K4602: Overview of the F5 security vulnerability response policy. BIG-IP and BIG-IQ +--------------+------+-----------------+----------+----------+---------------+ | | |Versions known to|Fixes |Severity/ |Vulnerable | |Product |Branch|be vulnerable^1 |introduced|CVSS score|component or | | | | |in | |feature | +--------------+------+-----------------+----------+----------+---------------+ |BIG-IP (all |All |None |Not |Not |None | |modules) | | |applicable|vulnerable| | +--------------+------+-----------------+----------+----------+---------------+ |BIG-IQ | | |Not |Not | | |Centralized |All |None |applicable|vulnerable|None | |Management | | | | | | +--------------+------+-----------------+----------+----------+---------------+ ^1F5 evaluates only software versions that have not yet reached the End of Technical Support (EoTS) phase of their lifecycle. For more information, refer to the Security hotfixes section of K4602: Overview of the F5 security vulnerability response policy. F5 Distributed Cloud and NGINX Services +-------------------------------+-----------------+---------------------------+ |Service |Severity/CVSS |Vulnerable component or | | |score |feature | +-------------------------------+-----------------+---------------------------+ |F5 Distributed Cloud (all |Not vulnerable |None | |services) | | | +-------------------------------+-----------------+---------------------------+ |F5 Silverline (all services) |Not vulnerable |None | +-------------------------------+-----------------+---------------------------+ |NGINX One Console |Not vulnerable |None | +-------------------------------+-----------------+---------------------------+ F5OS +-------+------+-------------------+-----------+-----------+------------------+ | | |Versions known to |Fixes |Severity/ |Vulnerable | |Product|Branch|be vulnerable^1 |introduced |CVSS score |component or | | | | |in | |feature | +-------+------+-------------------+-----------+-----------+------------------+ |F5OS-A |All |None |Not |Not |None | | | | |applicable |vulnerable | | +-------+------+-------------------+-----------+-----------+------------------+ |F5OS-C |All |None |Not |Not |None | | | | |applicable |vulnerable | | +-------+------+-------------------+-----------+-----------+------------------+ ^1F5 evaluates only software versions that have not yet reached the End of Technical Support (EoTS) phase of their lifecycle. For more information, refer to the Security hotfixes section of K4602: Overview of the F5 security vulnerability response policy. NGINX +----------+------+-------------+----------+----------+-----------------------+ | | |Versions |Fixes |Severity/ |Vulnerable component or| |Product |Branch|known to be |introduced|CVSS score|feature | | | |vulnerable^1 |in |^2 | | +----------+------+-------------+----------+----------+-----------------------+ | |37.x |None |37.0.0 |Medium/4.8| | | | | | |(CVSS | | |NGINX Plus+------+-------------+----------+v3.1) |ngx_http_charset_module| | | | |R36 P4 |Medium/6.3|module | | |Rx |R32 - R36 |R32 P6 |(CVSS | | | | | | |v4.0) | | +----------+------+-------------+----------+----------+-----------------------+ | | |1.0.0 - |1.31.0 |Medium/4.8| | | |1.x |1.30.0 |1.30.1 |(CVSS | | |NGINX Open| | | |v3.1) |ngx_http_charset_module| |Source +------+-------------+----------+Medium/6.3|module | | | |0.3.50 - |Will not |(CVSS | | | |0.x |0.9.7 |fix |v4.0) | | | | | | | | | +----------+------+-------------+----------+----------+-----------------------+ | | | | |Medium/4.8| | |NGINX | | | |(CVSS | | |Instance |2.x |2.16.0 - |None |v3.1) |Base NGINX Open Source | |Manager | |2.21.1 | |Medium/6.3|software components | | | | | |(CVSS | | | | | | |v4.0) | | +----------+------+-------------+----------+----------+-----------------------+ | | | | |Medium/4.8| | | | | | |(CVSS | | |F5 WAF for|5.x |5.9.0 - |None |v3.1) |Base NGINX Plus | |NGINX | |5.12.1 | |Medium/6.3|software components | | | | | |(CVSS | | | | | | |v4.0) | | +----------+------+-------------+----------+----------+-----------------------+ | |5.x |5.1.0 - 5.8.0|None |Medium/4.8| | |NGINX App | | | |(CVSS | | |Protect +------+-------------+----------+v3.1) |Base NGINX Plus | |WAF | |4.9.0 - | |Medium/6.3|software components | | |4.x |4.16.0 |None |(CVSS | | | | | | |v4.0) | | +----------+------+-------------+----------+----------+-----------------------+ | | | | |Medium/4.8| | | | | | |(CVSS | | |F5 DoS for|4.x |4.8.0 |None |v3.1) |Base NGINX Plus | |NGINX | | | |Medium/6.3|software components | | | | | |(CVSS | | | | | | |v4.0) | | +----------+------+-------------+----------+----------+-----------------------+ | | | | |Medium/4.8| | |NGINX App | | | |(CVSS | | |Protect |4.x |4.3.0 - 4.7.0|None |v3.1) |Base NGINX Plus | |DoS | | | |Medium/6.3|software components | | | | | |(CVSS | | | | | | |v4.0) | | +----------+------+-------------+----------+----------+-----------------------+ | | | | |Medium/4.8| | | |2.x |2.0.0 - 2.6.0|None |(CVSS | | |NGINX | | | |v3.1) |Base NGINX Plus or | |Gateway +------+-------------+----------+Medium/6.3|NGINX Open Source | |Fabric | | | |(CVSS |software components | | |1.x |1.3.0 - 1.6.2|None |v4.0) | | | | | | | | | +----------+------+-------------+----------+----------+-----------------------+ | |5.x |5.0.0 - 5.4.2|None | | | | | | | |Medium/4.8| | |NGINX +------+-------------+----------+(CVSS |Base NGINX Plus or | |Ingress |4.x |4.0.0 - 4.0.1|None |v3.1) |NGINX Open Source | |Controller| | | |Medium/6.3|software components | | +------+-------------+----------+(CVSS | | | |3.x |3.5.0 - 3.7.2|None |v4.0) | | | | | | | | | +----------+------+-------------+----------+----------+-----------------------+ |NGINX (all| | |Not |Not | | |other |All |None |applicable|vulnerable|None | |products) | | | | | | +----------+------+-------------+----------+----------+-----------------------+ ^1F5 evaluates only software versions that have not yet reached the End of Technical Support (EoTS) phase of their lifecycle. For more information, refer to the Security hotfixes section of K4602: Overview of the F5 security vulnerability response policy. ^2Starting with the August 2024 Quarterly Security Notification, F5 will provide the CVSS v4.0 base score in addition to the CVSS v3.1 score, for first-party security issues only. The CVSS score link takes you to a resource outside of MyF5, and the content may be removed without our knowledge. For more information about how F5 uses CVSS v4.0, refer to K000140363: Overview of CVSS v4.0 in F5 security advisories. Other products +-------+------+-------------------+-----------+-----------+------------------+ | | |Versions known to |Fixes |Severity/ |Vulnerable | |Product|Branch|be vulnerable^1 |introduced |CVSS score |component or | | | | |in | |feature | +-------+------+-------------------+-----------+-----------+------------------+ |Traffix|All |None |Not |Not |None | |SDC | | |applicable |vulnerable | | +-------+------+-------------------+-----------+-----------+------------------+ |F5 AI |All |None |Not |Not |None | |Gateway| | |applicable |vulnerable | | +-------+------+-------------------+-----------+-----------+------------------+ ^1F5 evaluates only software versions that have not yet reached the End of Technical Support (EoTS) phase of their lifecycle. For more information, refer to the Security hotfixes section of K4602: Overview of the F5 security vulnerability response policy. Security Advisory Recommended Actions If you are running a version listed in the Versions known to be vulnerable column, you can eliminate this vulnerability by installing a version listed in the Fixes introduced in column. If the Fixes introduced in column does not list a version for your branch, then no update candidate currently exists for that branch and F5 recommends that you upgrade to a version with the fix (refer to the tables). If the Fixes introduced in column lists a version prior to the one you are running, in the same branch, then your version should have the fix. Mitigation There is no mitigation; however, NGINX configurations that do not recode a UTF-8 response through charset_map are not affected. For more information about the ngx_http_charset_module module, refer to Module ngx_http_charset_module. Acknowledgments F5 acknowledges David Carlier and Zhenpeng (Leo) Lin (depthfirst) for bringing this issue to our attention and following the highest standards of coordinated disclosure. Related Content o K41942608: Overview of MyF5 security advisory articles o K12201527: Overview of Quarterly Security Notifications o K51812227: Understanding security advisory versioning o K4602: Overview of the F5 security vulnerability response policy o K4918: Overview of the F5 critical issue hotfix policy o K39757430: F5 product and services lifecycle policy index o K000090258: Download F5 products from MyF5 o K9970: Subscribe to email notifications regarding F5 products and security announcements o K9957: Creating a custom RSS feed to view new and updated documents o NGINX Glossary: What is a Control Plane? o NGINX Glossary: What is a Data Plane? o K000135931: Contact F5 Support - --------------------------END INCLUDED TEXT---------------------- You have received this e-mail bulletin as a result of your organisation's registration with AUSCERT. 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