CVE-2026-34835 | Rack up to 3.1.20/3.2.5 Regular Expression Rack::Request improper validation of syntactic correctness of input

VDB-354954 · CVE-2026-34835 · GCVE-0-2026-34835 RACK UP TO 3.1.20/3.2.5 REGULAR EXPRESSION RACK::REQUEST IMPROPER VALIDATION OF SYNTACTIC CORRECTNESS OF INPUT HISTORYDIFFRELATEJSONXMLCTI CVSS Meta Temp Score Current Exploit Price (≈) CTI Interest Score 5.1 $0-$5k 0.43+ 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. Upgrading to version 3.1.21 or 3.2.6 eliminates this vulnerability. Productinfo Name Rack Version 3.1.0 3.1.1 3.1.2 3.1.3 3.1.4 3.1.5 3.1.6 3.1.7 3.1.8 3.1.9 3.1.10 3.1.11 3.1.12 3.1.13 3.1.14 3.1.15 3.1.16 3.1.17 3.1.18 3.1.19 3.1.20 3.2.0 3.2.1 3.2.2 3.2.3 3.2.4 3.2.5 Website Product: https://github.com/rack/rack/ CPE 2.3info 🔒 🔒 🔒 CPE 2.2info 🔒 🔒 🔒 CVSSv4info VulDB Vector: 🔒 VulDB Reliability: 🔍 CVSSv3info VulDB Meta Base Score: 5.2 VulDB Meta Temp Score: 5.1 VulDB Base Score: 5.6 VulDB Temp Score: 5.4 VulDB Vector: 🔒 VulDB Reliability: 🔍 CNA Base Score: 4.8 CNA Vector (GitHub_M): 🔒 CVSSv2info Vector Complexity Authentication Confidentiality Integrity Availability Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock 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 Price Prediction: 🔍 Current Price Estimation: 🔒 0-Day Unlock Unlock Unlock Unlock Today Unlock Unlock Unlock Unlock 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 04/02/2026 +0 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 Entryinfo Created: 04/02/2026 19:36 Changes: 04/02/2026 19:36 (63) Complete: 🔍 Cache ID: 99:B5E:101 Discussion No comments yet. Languages: en. Please log in to comment. ◂ PreviousOverviewNext ▸