CVE-2026-34831

Rack is a modular Ruby web server interface. Prior to versions 2.2.23, 3.1.21, and 3.2.6, Rack::Files#fail sets the Content-Length response header using String#size instead of String#bytesize. When the response body contains multibyte UTF-8 characters, the declared Content-Length is smaller than the number of bytes actually sent on the wire. Because Rack::Files reflects the requested path in 404 responses, an attacker can trigger this mismatch by requesting a non-existent path containing percent-encoded UTF-8 characters. This results in incorrect HTTP response framing and may cause response desynchronization in deployments that rely on the incorrect Content-Length value. This issue has been patched in versions 2.2.23, 3.1.21, and 3.2.6.

CVSS v3 4.8 MEDIUM

4.8^/10

CVSS v3 : MEDIUM

Vector :

Exploitability : 2.2 / Impact : 2.5

Attack Vector NETWORK

Attack Complexity HIGH

Privileges Required NONE

User Interaction NONE

Confidentiality Impact LOW

Integrity Impact LOW

Availability Impact NONE

Scope UNCHANGED

References

Link	Resource
https://github.com/rack/rack/security/advisories/GHSA-q2ww-5357-x388	Vendor Advisory

Configurations

Configuration 1 (hide)

OR	cpe:2.3:a:rack:rack::::::ruby::*
	cpe:2.3:a:rack:rack::::::ruby::*
	cpe:2.3:a:rack:rack::::::ruby::*

History

No history.

Information

Published : 2026-04-02 17:16

Updated : 2026-07-24 21:10

NVD link : CVE-2026-34831

Mitre link : CVE-2026-34831

CVE.ORG link : CVE-2026-34831

JSON object : View

Products Affected

rack

rack

CWE

CWE-130

Improper Handling of Length Parameter Inconsistency

CWE-135

Incorrect Calculation of Multi-Byte String Length

{"id": "CVE-2026-34831", "cveTags": [], "metrics": {"ssvcV203": [{"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "ssvcData": {"id": "CVE-2026-34831", "role": "CISA Coordinator", "options": [{"exploitation": "none"}, {"automatable": "no"}, {"technicalImpact": "partial"}], "version": "2.0.3", "timestamp": "2026-04-03T17:43:52.462237Z"}}], "cvssMetricV31": [{"type": "Secondary", "source": "security-advisories@github.com", "cvssData": {"scope": "UNCHANGED", "version": "3.1", "baseScore": 4.8, "attackVector": "NETWORK", "baseSeverity": "MEDIUM", "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N", "integrityImpact": "LOW", "userInteraction": "NONE", "attackComplexity": "HIGH", "availabilityImpact": "NONE", "privilegesRequired": "NONE", "confidentialityImpact": "LOW"}, "impactScore": 2.5, "exploitabilityScore": 2.2}, {"type": "Primary", "source": "nvd@nist.gov", "cvssData": {"scope": "UNCHANGED", "version": "3.1", "baseScore": 6.5, "attackVector": "NETWORK", "baseSeverity": "MEDIUM", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N", "integrityImpact": "LOW", "userInteraction": "NONE", "attackComplexity": "LOW", "availabilityImpact": "NONE", "privilegesRequired": "NONE", "confidentialityImpact": "LOW"}, "impactScore": 2.5, "exploitabilityScore": 3.9}]}, "affected": [{"source": "security-advisories@github.com", "affectedData": [{"vendor": "rack", "product": "rack", "versions": [{"status": "affected", "version": "< 2.2.23"}, {"status": "affected", "version": ">= 3.0.0.beta1, < 3.1.21"}, {"status": "affected", "version": ">= 3.2.0, < 3.2.6"}]}]}], "published": "2026-04-02T17:16:26.420", "references": [{"url": "https://github.com/rack/rack/security/advisories/GHSA-q2ww-5357-x388", "tags": ["Vendor Advisory"], "source": "security-advisories@github.com"}], "vulnStatus": "Analyzed", "weaknesses": [{"type": "Secondary", "source": "security-advisories@github.com", "description": [{"lang": "en", "value": "CWE-130"}, {"lang": "en", "value": "CWE-135"}]}], "descriptions": [{"lang": "en", "value": "Rack is a modular Ruby web server interface. Prior to versions 2.2.23, 3.1.21, and 3.2.6, Rack::Files#fail sets the Content-Length response header using String#size instead of String#bytesize. When the response body contains multibyte UTF-8 characters, the declared Content-Length is smaller than the number of bytes actually sent on the wire. Because Rack::Files reflects the requested path in 404 responses, an attacker can trigger this mismatch by requesting a non-existent path containing percent-encoded UTF-8 characters. This results in incorrect HTTP response framing and may cause response desynchronization in deployments that rely on the incorrect Content-Length value. This issue has been patched in versions 2.2.23, 3.1.21, and 3.2.6."}, {"lang": "es", "value": "Rack es una interfaz modular de servidor web Ruby. Antes de las versiones 2.2.23, 3.1.21 y 3.2.6, Rack::Files#fail establece el encabezado de respuesta Content-Length usando String#size en lugar de String#bytesize. Cuando el cuerpo de la respuesta contiene caracteres UTF-8 multibyte, el Content-Length declarado es menor que el n\u00famero de bytes realmente enviados por la red. Debido a que Rack::Files refleja la ruta solicitada en las respuestas 404, un atacante puede desencadenar esta discrepancia solicitando una ruta inexistente que contenga caracteres UTF-8 codificados por porcentaje. Esto resulta en un encuadre incorrecto de la respuesta HTTP y puede causar desincronizaci\u00f3n de la respuesta en implementaciones que dependen del valor incorrecto de Content-Length. Este problema ha sido parcheado en las versiones 2.2.23, 3.1.21 y 3.2.6."}], "lastModified": "2026-07-24T21:10:00.143", "configurations": [{"nodes": [{"negate": false, "cpeMatch": [{"criteria": "cpe:2.3:a:rack:rack:*:*:*:*:*:ruby:*:*", "vulnerable": true, "matchCriteriaId": "AD5DE7DE-3A8B-4064-A7D5-1E117A101E81", "versionEndExcluding": "2.2.23"}, {"criteria": "cpe:2.3:a:rack:rack:*:*:*:*:*:ruby:*:*", "vulnerable": true, "matchCriteriaId": "6948AAA6-873D-46BA-AA22-4C81138128E1", "versionEndExcluding": "3.1.21", "versionStartIncluding": "3.0.0"}, {"criteria": "cpe:2.3:a:rack:rack:*:*:*:*:*:ruby:*:*", "vulnerable": true, "matchCriteriaId": "3FB592AD-E826-49BE-AC6D-E5F55FDCC96E", "versionEndExcluding": "3.2.6", "versionStartIncluding": "3.2.0"}], "operator": "OR"}]}], "sourceIdentifier": "security-advisories@github.com"}