Rack up to 3.1.20/3.2.5 Regular Expression Rack::Request improper validation of syntactic correctness of input

CVSS Meta Temp Score
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CTI Interest Score
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5.6$0-$5k0.45

Summaryinfo

A vulnerability described as problematic has been identified in Rack up to 3.1.20/3.2.5. The affected element is the function Rack::Request of the component Regular Expression Handler. The manipulation results in improper validation of syntactic correctness of input. This vulnerability is cataloged as CVE-2026-34835. The attack may be launched remotely. There is no exploit available. Upgrading the affected component is recommended.

Detailsinfo

A vulnerability, which was classified as problematic, was found in Rack up to 3.1.20/3.2.5. Affected is the function Rack::Request of the component Regular Expression Handler. The manipulation with an unknown input leads to a improper validation of syntactic correctness of input vulnerability. CWE is classifying the issue as CWE-1286. The product receives input that is expected to be well-formed - i.e., to comply with a certain syntax - but it does not validate or incorrectly validates that the input complies with the syntax. This is going to have an impact on confidentiality, integrity, and availability. CVE summarizes:

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.

The advisory is available at github.com. This vulnerability is traded as CVE-2026-34835 since 03/30/2026. The exploitability is told to be difficult. It is possible to launch the attack remotely. The exploitation doesn't require any form of authentication. Technical details are known, but there is no available exploit.

The vulnerability scanner Nessus provides a plugin with the ID 304841 (Linux Distros Unpatched Vulnerability : CVE-2026-34835), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 3.1.21 or 3.2.6 eliminates this vulnerability.

The vulnerability is also documented in the databases at Tenable (304841) and EUVD (EUVD-2026-18478). If you want to get best quality of vulnerability data, you may have to visit VulDB.

Productinfo

Name

Version

Website

CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 5.6
VulDB Meta Temp Score: 5.6

VulDB Base Score: 5.6
VulDB Temp Score: 5.4
VulDB Vector: 🔒
VulDB Reliability: 🔍

NVD Base Score: 6.5
NVD Vector: 🔒

CNA Base Score: 4.8
CNA Vector (GitHub_M): 🔒

CVSSv2info

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VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Improper validation of syntactic correctness of input
CWE: CWE-1286 / CWE-20
CAPEC: 🔒
ATT&CK: 🔒

Physical: No
Local: No
Remote: Yes

Availability: 🔒
Status: Not defined

EPSS Score: 🔒
EPSS Percentile: 🔒

Price Prediction: 🔍
Current Price Estimation: 🔒

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Nessus ID: 304841
Nessus Name: Linux Distros Unpatched Vulnerability : CVE-2026-34835

Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔒

Upgrade: Rack 3.1.21/3.2.6

Timelineinfo

03/30/2026 CVE reserved
04/02/2026 +3 days Advisory disclosed
04/02/2026 +0 days VulDB entry created
07/27/2026 +116 days VulDB entry last update

Sourcesinfo

Product: github.com

Advisory: github.com
Status: Confirmed

CVE: CVE-2026-34835 (🔒)
GCVE (CVE): GCVE-0-2026-34835
GCVE (VulDB): GCVE-100-354954
EUVD: 🔒

Entryinfo

Created: 04/02/2026 19:36
Updated: 07/27/2026 05:51
Changes: 04/02/2026 19:36 (63), 04/03/2026 00:36 (1), 04/06/2026 07:56 (2), 07/27/2026 05:51 (13)
Complete: 🔍
Cache ID: 216::103

If you want to get best quality of vulnerability data, you may have to visit VulDB.

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