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MEDIUM severity

CVE-2026-34763 — rack

MEDIUM

CVE-2026-34763 is a medium-severity (CVSS 5.3) CWE-625 vulnerability in rack. A fix is available for rack — see the affected versions and patch details below.

Rack: Rack::Directory info disclosure and DoS via unescaped regex interpolation

Also known asGHSA-7mqq-6cf9-v2qp
Published
Updated
Affected
3 pkgs
Patched
3 / 3
Exploits
None indexed
Exploitation data as of Nov 5, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

  • CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
  • CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-34763.

EPSS Exploitation Probability

via FIRST.org ↗
0.3%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs16th percentile — riskier than 16% of all scored CVEsHighest risk
0.00%0.28%0.55%0.83%0.0%0.3%May 26Sep 26Nov 26

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

3 pkgs affected
💎rack💎rack💎rack

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects RubyGems packages — download data is not available via public APIs for these ecosystems.

Description

Summary

Rack::Directory interpolates the configured root path directly into a regular expression when deriving the displayed directory path. If root contains regex metacharacters such as +, *, or ., the prefix stripping can fail and the generated directory listing may expose the full filesystem path in the HTML output.

Details

Rack::Directory::DirectoryBody#each computes the visible path using code equivalent to:

show_path = Utils.escape_html(path.sub(/\A#{root}/, ''))

Here, root is a developer-configured filesystem path. It is normalized earlier with File.expand_path(root) and then inserted directly into a regular expression without escaping.

Because the value is treated as regex syntax rather than as a literal string, metacharacters in the configured path can change how the prefix match behaves. When that happens, the expected root prefix is not removed from path, and the absolute filesystem path is rendered into the HTML directory listing.

Impact

If Rack::Directory is configured to serve a directory whose absolute path contains regex metacharacters, the generated directory listing may disclose the full server filesystem path instead of only the request-relative path.

This can expose internal deployment details such as directory layout, usernames, mount points, or naming conventions that would otherwise not be visible to clients.

Mitigation

  • Update to a patched version of Rack in which the root prefix is removed using an escaped regular expression.
  • Avoid using Rack::Directory with a root path that contains regular expression metacharacters.

Affected Packages

3 total 3 fixed
EcosystemPackageVulnerable rangeFix
💎RubyGemsrackall versions2.2.23bundle update rack --conservative
💎RubyGemsrack≥ 3.0.0.beta1&&< 3.1.213.1.21bundle update rack --conservative
💎RubyGemsrack≥ 3.2.0&&< 3.2.63.2.6bundle update rack --conservative

Affected Products

1 product · 3 configurations
Application
rackrack
≥ 3.2.0 && < 3.2.6
range

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for rack, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update rack to 2.2.23 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-34763 is resolved across your whole dependency graph.

  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.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatModerate
Workaround published by Red Hat
Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability.
Source: Red Hat security advisory for CVE-2026-34763 (CC BY 4.0)

Frequently Asked Questions

## Summary `Rack::Directory` interpolates the configured `root` path directly into a regular expression when deriving the displayed directory path. If `root` contains regex metacharacters such as `+`, `*`, or `.`, the prefix stripping can fail and the generated directory listing may expose the full filesystem path in the HTML output. ## Details `Rack::Directory::DirectoryBody#each` computes the visible path using code equivalent to: ```ruby show_path = Utils.escape_html(path.sub(/\A#{root}/, '')) ``` Here, `root` is a developer-configured filesystem path. It is normalized earlier with `Fi
O3 Security · Impact-Aware SCA

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CVE-2026-34763: rack — Fixed in 2.2.23