Incorrect Behavior Order: Validate Before Canonicalize in Rack - CVE-2026-34786
Published: April 2, 2026
Vulnerability identifier: #VU124836
CSH Severity: Medium
CVSS v4: 6.9 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N]
CVE-ID: CVE-2026-34786
CWE-ID: CWE-180
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote attacker to gain unauthorized access to otherwise restricted functionality.
The vulnerability exists due to incorrect behavior order when "Rack::Static#applicable_rules" evaluates several "header_rules" types. A remote attacker can request an encoded form of the path and bypass those headers.
Affected software
Rack
SUSE Linux Enterprise Server 15 SP6
SUSE Linux Enterprise Server 15 SP5
SUSE Linux Enterprise Server 15 SP4
SUSE Linux Enterprise Server for SAP Applications 15
SUSE Linux Enterprise Server 15
SUSE Linux Enterprise High Performance Computing LTSS 15
SUSE Linux Enterprise High Performance Computing ESPOS 15
SUSE Linux Enterprise High Performance Computing 15
SUSE Linux Enterprise Real Time 15
SUSE Manager Proxy
SUSE Manager Retail Branch Server
SUSE Manager Server
Ubuntu
Public Cloud Module
Server Applications Module
openSUSE Leap
ruby-rack (Ubuntu package)
rmt-server-config
rmt-server-pubcloud
rmt-server
rmt-server-debuginfo
rmt-server-debugsource
SUSE Linux Enterprise Server 15 SP6
SUSE Linux Enterprise Server 15 SP5
SUSE Linux Enterprise Server 15 SP4
SUSE Linux Enterprise Server for SAP Applications 15
SUSE Linux Enterprise Server 15
SUSE Linux Enterprise High Performance Computing LTSS 15
SUSE Linux Enterprise High Performance Computing ESPOS 15
SUSE Linux Enterprise High Performance Computing 15
SUSE Linux Enterprise Real Time 15
SUSE Manager Proxy
SUSE Manager Retail Branch Server
SUSE Manager Server
Ubuntu
Public Cloud Module
Server Applications Module
openSUSE Leap
ruby-rack (Ubuntu package)
rmt-server-config
rmt-server-pubcloud
rmt-server
rmt-server-debuginfo
rmt-server-debugsource
How to mitigate CVE-2026-34786
Install updates from vendor's website.
Rack - addressed in versions 2.2.23, 3.1.21, 3.2.6
ruby-rack (Ubuntu package) - addressed in versions 1.5.2-3+deb8u3ubuntu1~esm11, 1.6.4-3ubuntu0.2+esm10, 1.6.4-4ubuntu0.2+esm10, 2.0.7-2ubuntu0.1+esm10, 2.1.4-5ubuntu1.2+esm3, 2.2.7-1ubuntu0.7, 3.1.16-0.1ubuntu0.3
rmt-server-config - addressed in versions 2.27-150400.3.54.1, 2.27-150500.3.47.1, 2.27-150700.3.20.1
rmt-server-pubcloud - addressed in versions 2.27-150400.3.54.1, 2.27-150500.3.47.1, 2.27-150700.3.20.1
rmt-server - addressed in versions 2.27-150400.3.54.1, 2.27-150500.3.47.1, 2.27-150700.3.20.1
rmt-server-debuginfo - addressed in versions 2.27-150400.3.54.1, 2.27-150500.3.47.1, 2.27-150700.3.20.1
rmt-server-debugsource - addressed in versions 2.27-150400.3.54.1, 2.27-150500.3.47.1, 2.27-150700.3.20.1
ruby-rack (Ubuntu package) - addressed in versions 1.5.2-3+deb8u3ubuntu1~esm11, 1.6.4-3ubuntu0.2+esm10, 1.6.4-4ubuntu0.2+esm10, 2.0.7-2ubuntu0.1+esm10, 2.1.4-5ubuntu1.2+esm3, 2.2.7-1ubuntu0.7, 3.1.16-0.1ubuntu0.3
rmt-server-config - addressed in versions 2.27-150400.3.54.1, 2.27-150500.3.47.1, 2.27-150700.3.20.1
rmt-server-pubcloud - addressed in versions 2.27-150400.3.54.1, 2.27-150500.3.47.1, 2.27-150700.3.20.1
rmt-server - addressed in versions 2.27-150400.3.54.1, 2.27-150500.3.47.1, 2.27-150700.3.20.1
rmt-server-debuginfo - addressed in versions 2.27-150400.3.54.1, 2.27-150500.3.47.1, 2.27-150700.3.20.1
rmt-server-debugsource - addressed in versions 2.27-150400.3.54.1, 2.27-150500.3.47.1, 2.27-150700.3.20.1