Interpretation Conflict in Rack - CVE-2026-26961
Published: April 2, 2026
Vulnerability identifier: #VU124823
CSH Severity: Medium
CVSS v4: 6.3 [CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N]
CVE-ID: CVE-2026-26961
CWE-ID: CWE-436
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote attacker to compromise the target system.
The vulnerability exists due to the "Rack::Multipart::Parser" extracts the "boundary" parameter from multipart/form-data using a greedy regular expression. A remote attacker can bypass upstream filtering of uploaded files or form fields.
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-2026-26961
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