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.
Metrics
Affected Vendors & Products
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Advisories
| Source | ID | Title |
|---|---|---|
 Github GHSA |
GHSA-q2ww-5357-x388 | Rack has Content-Length mismatch in Rack::Files error responses |
Fixes
Solution
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Workaround
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References
History
Thu, 02 Apr 2026 20:30:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Description | 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. | |
| Title | Rack: Content-Length mismatch in Rack::Files error responses | |
| Weaknesses | CWE-130 CWE-135 |
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| Metrics |
cvssV3_1
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Projects
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MITRE
Status: PUBLISHED
Assigner: GitHub_M
Published:
Updated: 2026-04-02T16:43:08.762Z
Reserved: 2026-03-30T20:52:53.284Z
Link: CVE-2026-34831
Vulnrichment
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NVD
Status : Received
Published: 2026-04-02T17:16:26.420
Modified: 2026-04-02T17:16:26.420
Link: CVE-2026-34831
Redhat
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OpenCVE Enrichment
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