Resource exhaustion in Microsoft Internet Information Services (IIS) - CVE-2026-49975

Vulnerability identifier: #VU133362

CSH Severity: High

CVSS v4: 8.7 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N]

CVE-ID: CVE-2026-49975

CWE-ID: CWE-400

Exploitation vector: Remote access

Exploit availability: No public exploit available

The vulnerability allows a remote attacker to cause a denial of service.

The vulnerability exists due to uncontrolled resource consumption in the HTTP/2 request handling and HPACK header processing when handling crafted HTTP/2 requests that use repeated indexed header references and a stalled flow-control window. A remote attacker can send specially crafted HTTP/2 requests to cause a denial of service.

The issue is reachable in the default HTTP/2 configuration.

Microsoft Internet Information Services (IIS)
NGINX Open Source
Apache HTTP Server
Gentoo Linux
Debian Linux
SUSE Linux Enterprise Server 15 SP4
SUSE Linux Enterprise Server 15 SP5
SUSE Linux Enterprise Server 12 SP5
SUSE Linux Enterprise Server 12 SP5 LTSS Extended
SUSE Linux Enterprise Server 15 SP6
SUSE Linux Enterprise High Performance Computing 15
SUSE Linux Enterprise High Performance Computing ESPOS 15
SUSE Linux Enterprise High Performance Computing LTSS 15
SUSE Linux Enterprise Server 15
SUSE Linux Enterprise Server for SAP Applications 15
SUSE Linux Enterprise High Performance Computing 12
SUSE Linux Enterprise Server 12
SUSE Linux Enterprise Server for SAP Applications 12
SUSE Linux Enterprise Desktop 15
SUSE Linux Enterprise Real Time 15
Anolis OS
Red Hat Enterprise Linux for ARM 64
Red Hat Enterprise Linux for Power, little endian
Red Hat Enterprise Linux for IBM z Systems
Red Hat Enterprise Linux for x86_64
Red Hat Enterprise Linux Server - AUS
Red Hat Enterprise Linux Server - TUS
Red Hat Enterprise Linux for x86_64 - Extended Update Support
Red Hat Enterprise Linux for IBM z Systems - Extended Update Support
Red Hat Enterprise Linux for Power, little endian - Extended Update Support
Red Hat Enterprise Linux for ARM 64 - Extended Update Support
Ubuntu
Basesystem Module
SUSE Package Hub 15
Server Applications Module
openSUSE Leap
openEuler
FortiPAM
FortiSwitch Manager
FortiProxy
Red Hat Enterprise Linux Server for Power LE - Update Services for SAP Solutions
nginx (Ubuntu package)
mod_http2
http2 (Red Hat package)
compat-nginx-filesystem
nginx-mod-http-xslt-filter
nginx-mod-mail
nginx-mod-stream
compat-nginx-all-modules
nginx-debuginfo
compat-nginx-help
nginx-mod-http-perl
nginx-mod-http-image-filter
nginx-mod-devel
nginx-debugsource
compat-nginx-debuginfo
compat-nginx-mod-stream
compat-nginx-mod-mail
compat-nginx-mod-http-xslt-filter
nginx-all-modules
nginx-filesystem
nginx-help
compat-nginx-mod-http-perl
compat-nginx-mod-http-image-filter
compat-nginx-debugsource
nginx
compat-nginx
mod_md
mod_http2-debuginfo
mod_http2-debugsource
mod_http2-help
mod_http2-doc
apache2 (Ubuntu package)
httpd
httpd-manual
httpd-filesystem
mod_ssl
mod_session
mod_proxy_html
mod_ldap
httpd-tools
httpd-devel
httpd-debugsource
httpd-debuginfo
httpd-help
apache2-worker-debuginfo
apache2-tls13-doc
apache2-prefork-debuginfo
apache2
apache2-tls13-prefork-debuginfo
apache2-debuginfo
apache2-tls13-utils-debuginfo
apache2-prefork
apache2-utils
apache2-tls13
apache2-utils-debuginfo
apache2-tls13-worker
apache2-tls13-prefork
apache2-tls13-utils
apache2-tls13-debuginfo
apache2-example-pages
apache2-debugsource
apache2-tls13-worker-debuginfo
apache2-tls13-example-pages
apache2-tls13-debugsource
apache2-devel
apache2-worker
apache2-tls13-devel
apache2-doc
apache2-event
apache2-event-debuginfo
apache2-manual
apache2-worker-debugsource
apache2-prefork-debugsource
apache2-utils-debugsource
apache2-event-debugsource
apache2 (Debian package)
www-servers/apache
Zimbra Collaboration

Cybersecurity Help is currently unaware of any official solution to address this vulnerability.

FortiPAM - update to 1.9.2
NGINX Open Source - update to 1.29.8
Apache HTTP Server - update to 2.4.68
FortiSwitch Manager - update to 7.2.10
FortiProxy - addressed in versions 7.4.15, 7.6.7
Zimbra Collaboration - update to 10.1.18
nginx (Ubuntu package) - addressed in versions 1.4.6-1ubuntu3.9+esm8, 1.10.3-0ubuntu0.16.04.5+esm9, 1.14.0-0ubuntu1.11+esm4, 1.18.0-0ubuntu1.7+esm3, 1.18.0-6ubuntu14.13, 1.18.0-6ubuntu14.14, 1.18.0-6ubuntu14.15, 1.24.0-2ubuntu7.10, 1.24.0-2ubuntu7.11, 1.24.0-2ubuntu7.12, 1.28.0-6ubuntu1.5, 1.28.0-6ubuntu1.6, 1.28.0-6ubuntu1.7, 1.28.3-2ubuntu1.3, 1.28.3-2ubuntu1.4, 1.28.3-2ubuntu1.5
mod_http2 - addressed in versions 1.15.7-10, 2.0.41-1
http2 (Red Hat package) - addressed in versions 1.15.19-4.el9_2.8, 2.0.26-2.el9_4.3, 2.0.26-4.el9_6.2, 2.0.26-6.el9_8.1, 2.0.29-2.el10_0.2
compat-nginx-filesystem - update to 1.24.0-12
nginx-mod-http-xslt-filter - update to 1.24.0-12
nginx-mod-mail - update to 1.24.0-12
nginx-mod-stream - update to 1.24.0-12
compat-nginx-all-modules - update to 1.24.0-12
nginx-debuginfo - update to 1.24.0-12
compat-nginx-help - update to 1.24.0-12
nginx-mod-http-perl - update to 1.24.0-12
nginx-mod-http-image-filter - update to 1.24.0-12
nginx-mod-devel - update to 1.24.0-12
nginx-debugsource - update to 1.24.0-12
compat-nginx-debuginfo - update to 1.24.0-12
compat-nginx-mod-stream - update to 1.24.0-12
compat-nginx-mod-mail - update to 1.24.0-12
compat-nginx-mod-http-xslt-filter - update to 1.24.0-12
nginx-all-modules - update to 1.24.0-12
nginx-filesystem - update to 1.24.0-12
nginx-help - update to 1.24.0-12
compat-nginx-mod-http-perl - update to 1.24.0-12
compat-nginx-mod-http-image-filter - update to 1.24.0-12
compat-nginx-debugsource - update to 1.24.0-12
nginx - update to 1.24.0-12
compat-nginx - update to 1.24.0-12
mod_md - update to 2.0.8-8
mod_http2 - update to 2.0.25-5
mod_http2-debuginfo - update to 2.0.25-5
mod_http2-debugsource - update to 2.0.25-5
mod_http2-help - update to 2.0.25-5
mod_http2-doc - update to 2.0.41-1
apache2 (Ubuntu package) - addressed in versions 2.4.7-1ubuntu4.22+esm14, 2.4.18-2ubuntu3.17+esm19, 2.4.29-1ubuntu4.27+esm10, 2.4.41-4ubuntu3.23+esm5, 2.4.52-1ubuntu4.21, 2.4.58-1ubuntu8.13, 2.4.64-1ubuntu3.5, 2.4.66-2ubuntu2.2
httpd - update to 2.4.37-655.0.1
httpd-manual - update to 2.4.37-655.0.1
httpd-filesystem - update to 2.4.37-655.0.1
mod_ssl - update to 2.4.37-655.0.1
mod_session - update to 2.4.37-655.0.1
mod_proxy_html - update to 2.4.37-655.0.1
mod_ldap - update to 2.4.37-655.0.1
httpd-tools - update to 2.4.37-655.0.1
httpd-devel - update to 2.4.37-655.0.1
mod_md - addressed in versions 2.4.51-31, 2.4.58-16
mod_ldap - addressed in versions 2.4.51-31, 2.4.58-16
httpd-tools - addressed in versions 2.4.51-31, 2.4.58-16
httpd-devel - addressed in versions 2.4.51-31, 2.4.58-16
httpd-debugsource - addressed in versions 2.4.51-31, 2.4.58-16
httpd-debuginfo - addressed in versions 2.4.51-31, 2.4.58-16
httpd - addressed in versions 2.4.51-31, 2.4.58-16
mod_proxy_html - addressed in versions 2.4.51-31, 2.4.58-16
httpd-help - addressed in versions 2.4.51-31, 2.4.58-16
httpd-filesystem - addressed in versions 2.4.51-31, 2.4.58-16
mod_ssl - addressed in versions 2.4.51-31, 2.4.58-16
mod_session - addressed in versions 2.4.51-31, 2.4.58-16
apache2-worker-debuginfo - addressed in versions 2.4.66-35.81.1, 2.4.66-150400.6.57.1, 2.4.66-150600.5.55.1, 2.4.66-150700.4.23.1
apache2-tls13-doc - update to 2.4.66-35.81.1
apache2-prefork-debuginfo - addressed in versions 2.4.66-35.81.1, 2.4.66-150400.6.57.1, 2.4.66-150600.5.55.1, 2.4.66-150700.4.23.1
apache2 - addressed in versions 2.4.66-35.81.1, 2.4.66-150400.6.57.1, 2.4.66-150600.5.55.1, 2.4.66-150700.4.23.1
apache2-tls13-prefork-debuginfo - update to 2.4.66-35.81.1
apache2-debuginfo - addressed in versions 2.4.66-35.81.1, 2.4.66-150400.6.57.1, 2.4.66-150600.5.55.1, 2.4.66-150700.4.23.1
apache2-tls13-utils-debuginfo - update to 2.4.66-35.81.1
apache2-prefork - addressed in versions 2.4.66-35.81.1, 2.4.66-150400.6.57.1, 2.4.66-150600.5.55.1, 2.4.66-150700.4.23.1
apache2-utils - addressed in versions 2.4.66-35.81.1, 2.4.66-150400.6.57.1, 2.4.66-150600.5.55.1, 2.4.66-150700.4.23.1
apache2-tls13 - update to 2.4.66-35.81.1
apache2-utils-debuginfo - addressed in versions 2.4.66-35.81.1, 2.4.66-150400.6.57.1, 2.4.66-150600.5.55.1, 2.4.66-150700.4.23.1
apache2-tls13-worker - update to 2.4.66-35.81.1
apache2-tls13-prefork - update to 2.4.66-35.81.1
apache2-tls13-utils - update to 2.4.66-35.81.1
apache2-tls13-debuginfo - update to 2.4.66-35.81.1
apache2-example-pages - addressed in versions 2.4.66-35.81.1, 2.4.66-150400.6.57.1
apache2-debugsource - addressed in versions 2.4.66-35.81.1, 2.4.66-150400.6.57.1, 2.4.66-150600.5.55.1, 2.4.66-150700.4.23.1
apache2-tls13-worker-debuginfo - update to 2.4.66-35.81.1
apache2-tls13-example-pages - update to 2.4.66-35.81.1
apache2-tls13-debugsource - update to 2.4.66-35.81.1
apache2-devel - addressed in versions 2.4.66-35.81.1, 2.4.66-150400.6.57.1, 2.4.66-150600.5.55.1, 2.4.66-150700.4.23.1
apache2-worker - addressed in versions 2.4.66-35.81.1, 2.4.66-150400.6.57.1, 2.4.66-150600.5.55.1, 2.4.66-150700.4.23.1
apache2-tls13-devel - update to 2.4.66-35.81.1
apache2-doc - addressed in versions 2.4.66-35.81.1, 2.4.66-150400.6.57.1
apache2-event - addressed in versions 2.4.66-150400.6.57.1, 2.4.66-150600.5.55.1, 2.4.66-150700.4.23.1
apache2-event-debuginfo - addressed in versions 2.4.66-150400.6.57.1, 2.4.66-150600.5.55.1, 2.4.66-150700.4.23.1
apache2-manual - addressed in versions 2.4.66-150600.5.55.1, 2.4.66-150700.4.23.1
apache2-worker-debugsource - addressed in versions 2.4.66-150600.5.55.1, 2.4.66-150700.4.23.1
apache2-prefork-debugsource - addressed in versions 2.4.66-150600.5.55.1, 2.4.66-150700.4.23.1
apache2-utils-debugsource - addressed in versions 2.4.66-150600.5.55.1, 2.4.66-150700.4.23.1
apache2-event-debugsource - addressed in versions 2.4.66-150600.5.55.1, 2.4.66-150700.4.23.1
apache2 (Debian package) - addressed in versions 2.4.67-1~deb12u3, 2.4.67-1~deb13u3
www-servers/apache - update to 2.4.68

• https://blog.calif.io/p/codex-discovered-a-hidden-http2-bomb
• https://github.com/califio/publications/tree/main/MADBugs/http2-bomb

• Resource exhaustion in Microsoft IIS HTTP/2 support
• Resource exhaustion in nginx HTTP/2 support
• Multiple vulnerabilities in Apache HTTP Server
• Ubuntu update for apache2
• Debian update for apache2
• Anolis OS update for mod_http2
• Ubuntu update for nginx
• Red Hat Enterprise Linux 9 update for mod_http2
• Red Hat Enterprise Linux 8 update for the httpd:2.4 module
• Ubuntu update for nginx
• Anolis OS update for httpd:2.4 module
• openEuler 24.03 LTS SP1 update for httpd
• openEuler 22.03 LTS SP4 update for httpd
• openEuler 24.03 LTS SP3 update for httpd
• openEuler update for nginx
• openEuler update for mod_http2
• Ubuntu update for nginx
• Denial of service when handling HTTP/2 requests in Zimbra Collaboration
• SUSE update for apache2
• SUSE update for apache2
• Ubuntu update for nginx
• SUSE update for apache2
• SUSE update for apache2
• Red Hat Enterprise Linux 8 update for the httpd:2.4 module
• Red Hat Enterprise Linux 8 update for the httpd:2.4 module
• Red Hat Enterprise Linux 8 update for the httpd:2.4 module
• Ubuntu update for apache2
• Red Hat Enterprise Linux 10 update for mod_http2
• Red Hat Enterprise Linux 9 update for mod_http2
• Fortinet products update for HTTP/2 Bomb vulnerability in Apache HTTP server
• Gentoo update for Apache HTTPD
• Red Hat Enterprise Linux 9 update for mod_http2
• Red Hat Enterprise Linux 9 update for mod_http2