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CVE-2026-34830: Rack: Rack::Sendfile regex injection via HTTP_X_ACCEL_MAPPING header allows arbitrary file reads through nginx
- Severity: high (CVSS 7.5 v3.1)
- Exploited in the wild: not listed in CISA KEV
- EPSS: 0.2% probability of exploitation in the next 30 days
- Public exploit or detection template: none known
- Published: 2026-04-02 · updated 2026-07-24
- Weakness: CWE-625
Description
Rack is a modular Ruby web server interface. Prior to versions 2.2.23, 3.1.21, and 3.2.6, Rack::Sendfile#map_accel_path interpolates the value of the X-Accel-Mapping request header directly into a regular expression when rewriting file paths for X-Accel-Redirect. Because the header value is not escaped, an attacker who can supply X-Accel-Mapping to the backend can inject regex metacharacters and control the generated X-Accel-Redirect response header. In deployments using Rack::Sendfile with x-accel-redirect, this can allow an attacker to cause nginx to serve unintended files from configured internal locations. This issue has been patched in versions 2.2.23, 3.1.21, and 3.2.6.
Affected products
- rack: before 2.2.23; from 3.0.0 before 3.1.21; from 3.2.0 before 3.2.6 — fixed in 2.2.23, 3.1.21, 3.2.6
- Rubygems Rack: before 2.2.23; from 3.0.0.beta1 before 3.1.21; from 3.2.0 before 3.2.6; 0.1.0, 0.2.0, 0.3.0, 0.4.0, 0.9.0, 0.9.1 (+169) — fixed in 2.2.23, 3.1.21, 3.2.6
How to fix
Upgrade to a fixed version: rack 2.2.23, 3.1.21, 3.2.6; Rubygems Rack 2.2.23, 3.1.21, 3.2.6. Check the vendor advisory for mitigations.
References
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