CVE-2026-34786 Rack: Rack::Static header_rules bypass via URL-encoded paths
Attackers can bypass security headers on static files by using URL-encoded paths, affecting Rack deployments relying on header_rules.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-34786?
CVE-2026-34786 is a medium-severity vulnerability in rack, published on 2 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Rack is a modular Ruby web server interface. Prior to versions 2.2.23, 3.1.21, and 3.2.6, Rack::Static#applicable_rules evaluates several header_rules types against the raw URL-encoded PATH_INFO, while the underlying file-serving path is decoded before the file is served. As a result, a request for a URL-encoded variant of a static path can serve the same file without the headers that header_rules were intended to apply. In deployments that rely on Rack::Static to attach security-relevant response headers to static content, this can allow an attacker to bypass those headers by requesting an encoded form of the path. This issue has been patched in versions 2.2.23, 3.1.21, and 3.2.6.
Weakness: CWE-180
Which versions are affected by CVE-2026-34786?
6 open source packages ship an affected version, including rack. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
rack RubyGems | All versions | 2.2.23 |
rack RubyGems | All versions | 2.2.23 |
rack RubyGems | From 3.0.0.beta1 | 3.1.21 |
rack RubyGems | From 3.0.0.beta1 | 3.1.21 |
rack RubyGems | From 3.2.0 | 3.2.6 |
rack RubyGems | From 3.2.0 | 3.2.6 |
Products include Rack Rack.
How do I fix CVE-2026-34786?
Upgrade rack to a fixed version for your release line: 2.2.23, 3.1.21 or 3.2.6.
Is CVE-2026-34786 being exploited?
There is no known exploitation of CVE-2026-34786 in the wild and no public exploit code.
Other vulnerabilities in rack
- CVE-2026-34785 Rack: Local file inclusion in `Rack::Static` via URL Prefix Matching
- CVE-2026-34827 Rack: Algorithmic-Complexity DoS in Rack::Multipart::Parser
- CVE-2026-34829 Rack: Denial of Service via Unbounded Multipart File Upload Without Content-Length
- CVE-2026-22860 Rack has a Directory Traversal via Rack:Directory
- CVE-2025-61919 Rack is vulnerable to a memory-exhaustion DoS through unbounded URL-encoded body parsing
Sources
Also known as DEBIAN-CVE-2026-34786, GHSA-q4qf-9j86-f5mh, MINI-245v-8gf2-gh9w, MINI-2744-9838-hgqj, MINI-4fwj-xvm8-pgwx, MINI-4p3p-vxxr-c8jq and 21 more.