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Vulnerability details: VCID-5twm-pqc2-xyfn
Vulnerability ID VCID-5twm-pqc2-xyfn
Aliases CVE-2026-34835
GHSA-g2pf-xv49-m2h5
Summary 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.
Status Published
Exploitability 0.5
Weighted Severity 6.2
Risk 3.1
Affected and Fixed Packages Package Details
Weaknesses (1)
CWE-1286 Improper Validation of Syntactic Correctness of Input
System Score Found at
cvssv3 4.8 https://access.redhat.com/hydra/rest/securitydata/cve/CVE-2026-34835.json
epss 0.00064 https://api.first.org/data/v1/epss?cve=CVE-2026-34835
epss 0.00064 https://api.first.org/data/v1/epss?cve=CVE-2026-34835
epss 0.00103 https://api.first.org/data/v1/epss?cve=CVE-2026-34835
epss 0.00103 https://api.first.org/data/v1/epss?cve=CVE-2026-34835
epss 0.00103 https://api.first.org/data/v1/epss?cve=CVE-2026-34835
epss 0.00103 https://api.first.org/data/v1/epss?cve=CVE-2026-34835
epss 0.00103 https://api.first.org/data/v1/epss?cve=CVE-2026-34835
cvssv3.1 4.8 https://ftp.suse.com/pub/projects/security/yaml/suse-cvss-scores.yaml
cvssv3.1_qr MODERATE https://github.com/advisories/GHSA-g2pf-xv49-m2h5
cvssv3.1 4.8 https://github.com/rack/rack
generic_textual MODERATE https://github.com/rack/rack
cvssv3.1 4.8 https://github.com/rack/rack/security/advisories/GHSA-g2pf-xv49-m2h5
cvssv3.1_qr MODERATE https://github.com/rack/rack/security/advisories/GHSA-g2pf-xv49-m2h5
generic_textual MODERATE https://github.com/rack/rack/security/advisories/GHSA-g2pf-xv49-m2h5
ssvc Track https://github.com/rack/rack/security/advisories/GHSA-g2pf-xv49-m2h5
cvssv3.1 4.8 https://nvd.nist.gov/vuln/detail/CVE-2026-34835
generic_textual MODERATE https://nvd.nist.gov/vuln/detail/CVE-2026-34835
Reference id Reference type URL
https://access.redhat.com/hydra/rest/securitydata/cve/CVE-2026-34835.json
https://api.first.org/data/v1/epss?cve=CVE-2026-34835
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2026-34835
https://ftp.suse.com/pub/projects/security/yaml/suse-cvss-scores.yaml
https://github.com/rack/rack
https://nvd.nist.gov/vuln/detail/CVE-2026-34835
2454482 https://bugzilla.redhat.com/show_bug.cgi?id=2454482
GHSA-g2pf-xv49-m2h5 https://github.com/advisories/GHSA-g2pf-xv49-m2h5
GHSA-g2pf-xv49-m2h5 https://github.com/rack/rack/security/advisories/GHSA-g2pf-xv49-m2h5
No exploits are available.
Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N Found at https://access.redhat.com/hydra/rest/securitydata/cve/CVE-2026-34835.json
Attack Vector (AV) Attack Complexity (AC) Privileges Required (PR) User Interaction (UI) Scope (S) Confidentiality Impact (C) Integrity Impact (I) Availability Impact (A)

network

adjacent_network

local

physical

low

high

none

low

high

none

required

unchanged

changed

high

low

none

high

low

none

high

low

none
Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N Found at https://ftp.suse.com/pub/projects/security/yaml/suse-cvss-scores.yaml
Attack Vector (AV) Attack Complexity (AC) Privileges Required (PR) User Interaction (UI) Scope (S) Confidentiality Impact (C) Integrity Impact (I) Availability Impact (A)

network

adjacent_network

local

physical

low

high

none

low

high

none

required

unchanged

changed

high

low

none

high

low

none

high

low

none
Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N Found at https://github.com/rack/rack
Attack Vector (AV) Attack Complexity (AC) Privileges Required (PR) User Interaction (UI) Scope (S) Confidentiality Impact (C) Integrity Impact (I) Availability Impact (A)

network

adjacent_network

local

physical

low

high

none

low

high

none

required

unchanged

changed

high

low

none

high

low

none

high

low

none
Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N Found at https://github.com/rack/rack/security/advisories/GHSA-g2pf-xv49-m2h5
Attack Vector (AV) Attack Complexity (AC) Privileges Required (PR) User Interaction (UI) Scope (S) Confidentiality Impact (C) Integrity Impact (I) Availability Impact (A)

network

adjacent_network

local

physical

low

high

none

low

high

none

required

unchanged

changed

high

low

none

high

low

none

high

low

none
Vector: SSVCv2/E:N/A:N/T:P/P:M/B:A/M:M/D:T/2026-04-02T17:43:54Z/ Found at https://github.com/rack/rack/security/advisories/GHSA-g2pf-xv49-m2h5
Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N Found at https://nvd.nist.gov/vuln/detail/CVE-2026-34835
Attack Vector (AV) Attack Complexity (AC) Privileges Required (PR) User Interaction (UI) Scope (S) Confidentiality Impact (C) Integrity Impact (I) Availability Impact (A)

network

adjacent_network

local

physical

low

high

none

low

high

none

required

unchanged

changed

high

low

none

high

low

none

high

low

none
Exploit Prediction Scoring System (EPSS)
Percentile 0.20158
EPSS Score 0.00064
Published At April 4, 2026, 12:55 p.m.
Date Actor Action Source VulnerableCode Version
2026-04-03T02:49:30.277815+00:00 Vulnrichment Import https://github.com/cisagov/vulnrichment/blob/develop/2026/34xxx/CVE-2026-34835.json 38.1.0