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HIGH severity

CVE-2026-38969 — webrick

HIGHFix: ruby/webrick#199

CVE-2026-38969 is a high-severity (CVSS 7.5) vulnerability. A fix is available — see the affected versions and patch details below.

Published
Jul 2, 2026
Updated
Jul 16, 2026
Affected
12 versions
Patched
See advisory
Exploits
None indexed
Exploitation data as of Jul 16, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Description

ruby webrick through v1.9.2 WEBrick reparses trailer Content-Length into canonical request state, enabling request smuggling. NOTE: the Supplier reports that "The project README states that it is suitable for testing and development, and that its developers do not encourage its use to serve production web applications that may be subject to hostile input. It is not a production web server and is not intended to receive traffic from untrusted sources. Request smuggling is only reachable when WEBrick sits behind a proxy and receives hostile traffic in a production deployment, which is the configuration the project documents as discouraged."

Detection & mitigation playbook

Vulnerability

  1. Detect

    Identify every host running the affected component and compare the installed build against the fixed version below — for source-built or distro-packaged software the version string, not a lockfile, is the source of truth (`dpkg -l`, `rpm -q`, or the binary's own `--version`).

  2. Fix

    Upgrade the affected component to the fixed release for CVE-2026-38969, or apply your distribution's backported patch — distro builds are often patched at an older version number, so check your vendor's advisory rather than the upstream version alone.

  3. Workarounds

    If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Frequently Asked Questions

ruby webrick through v1.9.2 WEBrick reparses trailer Content-Length into canonical request state, enabling request smuggling. NOTE: the Supplier reports that "The project README states that it is suitable for testing and development, and that its developers do not encourage its use to serve production web applications that may be subject to hostile input. It is not a production web server and is not intended to receive traffic from untrusted sources. Request smuggling is only reachable when WEBrick sits behind a proxy and receives hostile traffic in a production deployment, which is the config
O3 Security · Impact-Aware SCA

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CVE-2026-38969: webrick (High 7.5) | O3 Security