What is CVE-2026-34831?

CVE-2026-34831 is a medium-severity vulnerability in Rack, classified under Improper Handling of Length Parameter Inconsistency. CVSS score: 4.8/10. Published 2026-04-02.

How severe is CVE-2026-34831?

Medium severity. CVSS v3 base score is 4.8 out of 10.

Vulnerability in Rack

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-…

EPSS: 0.000 (12.9th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 4.8 (Medium). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N.

Affected products

Rack — versions < 2.2.23, >= 3.0.0.beta1, < 3.1.21, >= 3.2.0, < 3.2.6

Weakness classification (CWE)

CWE-130 — Improper Handling of Length Parameter Inconsistency
CWE-135 — Incorrect Calculation of Multi-Byte String Length

References

https://github.com/rack/rack/security/advisories/GHSA-q2ww-5357-x388 (x_refsource_CONFIRM)

Frequently asked questions

What is CVE-2026-34831?: CVE-2026-34831 is a medium-severity vulnerability in Rack, classified under Improper Handling of Length Parameter Inconsistency. CVSS score: 4.8/10. Published 2026-04-02.
How severe is CVE-2026-34831?: Medium severity. CVSS v3 base score is 4.8 out of 10.