TI-2026-27030 Aliases CVE-2026-34786 GHSA-q4qf-9j86-f5mh

Rack: Rack::Static header_rules bypass via URL-encoded paths

LOW 29CWE-180Published 2026-04-02 · Updated 2026-04-03

Key facts

Attack vector: Network
Privileges required: None
User interaction: None
Attack complexity: Low
Impact type: —
Confidentiality · integrity · availability: None · Low · None
Fix status: Partial Red Hat: 6 without a fix

Attack profile from CVSS 3.1 · CNA. Fix status from CNA, GitHub and Red Hat.

Summary

Rack is a modular Ruby web server interface. Prior to versions 2.2.23, 3.1.21, and 3.2.6, Rack::Static#applicable_rules evaluates several header_rules types against the raw URL-encoded PATH_INFO, while the underlying file-serving path is decoded before the file is served. As a result, a request for a URL-encoded variant of a static path can serve the same file without the headers that header_rules were intended to apply. In deployments that rely on Rack::Static to attach security-relevant response headers to static content, this can allow an attacker to bypass those headers by requesting an encoded form of the path. This issue has been patched in versions 2.2.23, 3.1.21, and 3.2.6.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV

EPSS 0.00202 10th percentileScored 2026-11-07

Fix Partial rack (rack): 2.2.23, 3.1.21, 3.2.6rack (RubyGems): 2.2.23, 3.1.21, 3.2.6Red Hat: 6 without a fix

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation: None
Automatable: Yes
Technical impact: Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

Vendor	Product	Affected versions	Fixed in	Status	Source
rack	rack	before 2.2.23; 3.0.0.beta1 to before 3.1.21; 3.2.0 to before 3.2.6	2.2.23, 3.1.21, 3.2.6	Patch available	CNA
—	rack (RubyGems)	before 2.2.23	2.2.23	Patch available	GHSA-q4qf-9j86-f5mh
—	rack (RubyGems)	3.0.0.beta1 to before 3.1.21	3.1.21	Patch available	GHSA-q4qf-9j86-f5mh
—	rack (RubyGems)	3.2.0 to before 3.2.6	3.2.6	Patch available	GHSA-q4qf-9j86-f5mh

rack Vendorrack Affected before 2.2.23; 3.0.0.beta1 to before 3.1.21; 3.2.0 to before 3.2.6 Fixed in 2.2.23, 3.1.21, 3.2.6 Patch available CNA
rack (RubyGems) Vendor— Affected before 2.2.23 Fixed in 2.2.23 Patch available GHSA-q4qf-9j86-f5mh
rack (RubyGems) Vendor— Affected 3.0.0.beta1 to before 3.1.21 Fixed in 3.1.21 Patch available GHSA-q4qf-9j86-f5mh
rack (RubyGems) Vendor— Affected 3.2.0 to before 3.2.6 Fixed in 3.2.6 Patch available GHSA-q4qf-9j86-f5mh

CPE configurations NVD · 1

CPE	Versions	Role	Vendor
cpe:2.3:a:rack:rack::::::ruby::*	before 2.2.23; 3.0.0 to before 3.1.21; 3.2.0 to before 3.2.6	Vulnerable	rack

cpe:2.3:a:rack:rack:*:*:*:*:*:ruby:*:* Versions before 2.2.23; 3.0.0 to before 3.1.21; 3.2.0 to before 3.2.6 Vulnerable ·rack

Remediation

Fix · CNA rack (rack) Fixed in 2.2.23, 3.1.21, 3.2.6
Fix · GHSA-q4qf-9j86-f5mh rack (RubyGems) Fixed in 2.2.23 Advisory →
Fix · GHSA-q4qf-9j86-f5mh rack (RubyGems) Fixed in 3.1.21 Advisory →
Fix · GHSA-q4qf-9j86-f5mh rack (RubyGems) Fixed in 3.2.6 Advisory →

Vendor assessments

Red Hat

Red Hat rating: Moderate. Red Hat's page for this CVE →

Product	Status	Plan or fix
Logging Subsystem for Red Hat OpenShift	Affected	No fix yet: Fix deferred
Red Hat 3scale API Management Platform 2	Affected	No fix yet: Fix deferred
Red Hat Enterprise Linux 10	Affected	No fix yet: Fix deferred
Red Hat Enterprise Linux 7	Affected	No fix yet: Fix deferred
Red Hat Enterprise Linux 8	Affected	No fix yet: Fix deferred
Red Hat Enterprise Linux 9	Affected	No fix yet: Fix deferred

Timeline

2026-10-02 Threatist record created from CVE-2026-34786
2026-10-03 Alias added: GHSA-q4qf-9j86-f5mh

References

Advisory 2

Other 2

TI-2024-16580 Rack ReDos in content type parsing (2nd degree polynomial) CVSS 3.1HIGH 7.5
TI-2024-17236 Possible Denial of Service Vulnerability in Rack Header Parsing CVSS 3.1HIGH 7.5
TI-2024-17231 Possible DoS Vulnerability with Range Header in Rack CVSS 3.1HIGH 7.5
TI-2023-12254 Uncontrolled resource consumption in https://github.com/rack/rack CVSS 3.1HIGH 7.5
TI-2025-38165 Rack's multipart parser buffers unbounded per-part headers, enabling DoS (memory exhaustion) CVSS 3.1HIGH 7.5
TI-2025-38163 Rack's unbounded multipart preamble buffering enables DoS (memory exhaustion) CVSS 3.1HIGH 7.5

See all 36 →

Sources

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