CVE & CISA-KEV Catalog

CVE-2026-34835

MEDIUM
4.8
CVSS v3
NVD

Description

Rack is a modular Ruby web server interface. From versions 3.0.0.beta1 to before 3.1.21, and 3.2.0 to before 3.2.6, Rack::Request parses the Host header using an AUTHORITY regular expression that accepts characters not permitted in RFC-compliant hostnames, including /, ?, #, and @. Because req.host returns the full parsed value, applications that validate hosts using naive prefix or suffix checks can be bypassed. This can lead to host header poisoning in applications that use req.host, req.url, or req.base_url for link generation, redirects, or origin validation. This issue has been patched in versions 3.1.21 and 3.2.6.

CWE-1286

How to fix

Remediation Available
ruby-rackDebian
Fixed in:3.2.6-2CVE-2026-34835
librack-rubyUbuntu
Fixed in:1.5.2-3+deb8u3ubuntu1~esm11USN-8182-1
librack-ruby1.8Ubuntu
Fixed in:1.5.2-3+deb8u3ubuntu1~esm11USN-8182-1
librack-ruby1.9.1Ubuntu
Fixed in:1.5.2-3+deb8u3ubuntu1~esm11USN-8182-1
ruby-rackUbuntu
Fixed in:1.5.2-3+deb8u3ubuntu1~esm11USN-8182-1
Fixed in:1.6.4-3ubuntu0.2+esm10USN-8182-1
Fixed in:1.6.4-4ubuntu0.2+esm10USN-8182-1
Fixed in:2.0.7-2ubuntu0.1+esm10USN-8182-1
Fixed in:2.1.4-5ubuntu1.2+esm3USN-8182-1
Fixed in:2.2.7-1ubuntu0.7USN-8182-1
Fixed in:3.1.16-0.1ubuntu0.3USN-8182-1

Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.

CVSS v3 Vector

Exploitability

Attack VectorNetwork
Attack ComplexityHigh
Privileges RequiredNone
User InteractionNone
ScopeUnchanged

Impact

ConfidentialityLow
IntegrityLow
AvailabilityNone

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N

Exploit Intelligence

0.19%probability of exploitation in 30 days
9thpercentile

Low risk: more likely to be exploited than 9% of all known CVEs.

References

Exploit1
Embed a live status badge for CVE-2026-34835
CVE-2026-34835 severity badge

Markdown

[![CVE-2026-34835](https://tridentstack.com/cve/badge/CVE-2026-34835.svg)](https://tridentstack.com/cve/CVE-2026-34835)

HTML

<a href="https://tridentstack.com/cve/CVE-2026-34835"><img src="https://tridentstack.com/cve/badge/CVE-2026-34835.svg" alt="CVE-2026-34835"></a>

Find and fix vulnerabilities across your fleet

TridentStack Control continuously scans your Windows, macOS, and Linux fleet for known vulnerabilities, prioritizes them by severity and active exploitation, and patches them automatically.

Start free

This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-04-03.