Rack: Denial of Service via Unbounded Multipart File Upload Without Content-Length

Summary

CVE	CVE-2026-34829
State	PUBLISHED
Assigner	GitHub_M
Source Priority	CVE Program / NVD first with legacy fallback
Published	2026-04-02 17:16:26 UTC
Updated	2026-06-30 03:18:59 UTC
Description	Rack is a modular Ruby web server interface. Prior to versions 2.2.23, 3.1.21, and 3.2.6, Rack::Multipart::Parser only wraps the request body in a BoundedIO when CONTENT_LENGTH is present. When a multipart/form-data request is sent without a Content-Length header, such as with HTTP chunked transfer encoding, multipart parsing continues until end-of-stream with no total size limit. For file parts, the uploaded body is written directly to a temporary file on disk rather than being constrained by the buffered in-memory upload limit. An unauthenticated attacker can therefore stream an arbitrarily large multipart file upload and consume unbounded disk space. This results in a denial of service condition for Rack applications that accept multipart form data. This issue has been patched in versions 2.2.23, 3.1.21, and 3.2.6.

Risk And Classification

Primary CVSS: v3.1 7.5 HIGH from ADP

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

EPSS: 0.000410000 probability, percentile 0.124700000 (date 2026-04-07)

Problem Types: CWE-400 | CWE-770 | CWE-400 CWE-400: Uncontrolled Resource Consumption | CWE-770 CWE-770: Allocation of Resources Without Limits or Throttling | CWE-770 Allocation of Resources Without Limits or Throttling

Version	Source	Type	Score	Severity	Vector
3.1	ADP	CVSS	7.5	HIGH	`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`
3.1	[email protected]	Secondary	7.5	HIGH	`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`
3.1	0b0ca135-0b70-47e7-9f44-1890c2a1c46c	Secondary	7.5	HIGH	`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`
3.1	CNA	DECLARED	7.5	HIGH	`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`

CVSS v3.1 Breakdown

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

None

Availability

High

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

NVD Known Affected Configurations (CPE 2.3)

Type	Vendor	Product	Version	Update	Edition	Language
Application	Rack	Rack	All	All	All	All

Vendor Declared Affected Products

Source	Vendor	Product	Version	Platforms
CNA	Rack	Rack	affected < 2.2.23	Not specified
CNA	Rack	Rack	affected >= 3.0.0.beta1, < 3.1.21	Not specified
CNA	Rack	Rack	affected >= 3.2.0, < 3.2.6	Not specified
ADP	Red Hat	Logging Subsystem For Red Hat OpenShift	Not specified	Not specified
ADP	Red Hat	Red Hat 3scale API Management Platform 2	Not specified	Not specified
ADP	Red Hat	Red Hat Enterprise Linux 10	Not specified	Not specified
ADP	Red Hat	Red Hat Enterprise Linux 7	Not specified	Not specified
ADP	Red Hat	Red Hat Enterprise Linux 8	Not specified	Not specified
ADP	Red Hat	Red Hat Enterprise Linux 9	Not specified	Not specified

References

Reference	Source	Link	Tags
security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-34829.json	0b0ca135-0b70-47e7-9f44-1890c2a1c46c	security.access.redhat.com
github.com/rack/rack/security/advisories/GHSA-8vqr-qjwx-82mw	[email protected]	github.com	Vendor Advisory
bugzilla.redhat.com/show_bug.cgi	0b0ca135-0b70-47e7-9f44-1890c2a1c46c	bugzilla.redhat.com
access.redhat.com/security/cve/CVE-2026-34829	0b0ca135-0b70-47e7-9f44-1890c2a1c46c	access.redhat.com
CVE Program record	CVE.ORG	www.cve.org	canonical
NVD vulnerability detail	NVD	nvd.nist.gov	canonical, analysis

No vendor comments have been submitted for this CVE.

Additional Advisory Data

Source	Time	Event
ADP	2026-04-02T18:01:19.914Z	Reported to Red Hat.
ADP	2026-04-02T16:46:47.357Z	Made public.

Workarounds

ADP: Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability.

There are currently no legacy QID mappings associated with this CVE.