Improper Validation of Syntactic Correctness of Input in Rack - CVE-2026-34835
Published: April 2, 2026
Vulnerability identifier: #VU124830
CSH Severity: Medium
CVSS v4: 6.3 [CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N]
CVE-ID: CVE-2026-34835
CWE-ID: CWE-1286
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::Request" accepts invalid Host characters. A remote attacker can bypass host allowlists and poison generated links, redirects, or origin-dependent security decisions.
Affected software
Rack
Ubuntu
ruby-rack (Ubuntu package)
Ubuntu
ruby-rack (Ubuntu package)
How to mitigate CVE-2026-34835
Install updates from vendor's website.
Rack - addressed in versions 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
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