CVE-2026-34831
Publication date 2 April 2026
Last updated 23 April 2026
Ubuntu priority
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.
Status
| Package | Ubuntu Release | Status |
|---|---|---|
| ruby-rack | 25.10 questing |
Fixed 3.1.16-0.1ubuntu0.3
|
| 24.04 LTS noble |
Fixed 2.2.7-1ubuntu0.7
|
|
| 22.04 LTS jammy |
Fixed 2.1.4-5ubuntu1.2+esm3
|
|
| 20.04 LTS focal |
Not affected
|
|
| 18.04 LTS bionic |
Not affected
|
|
| 16.04 LTS xenial |
Not affected
|
|
| 14.04 LTS trusty |
Not affected
|
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Severity score breakdown
| Parameter | Value |
|---|---|
| Base score |
4.8 · Medium
|
| Attack vector | Network |
| Attack complexity | High |
| Privileges required | None |
| User interaction | None |
| Scope | Unchanged |
| Confidentiality | Low |
| Integrity impact | Low |
| Availability impact | None |
| Vector | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N |
References
Related Ubuntu Security Notices (USN)
- USN-8182-1
- Rack vulnerabilities
- 17 April 2026