CVE-2026-34830 — Rack: Rack::Sendfile regex injection via HTTP_X_ACCEL_MAPPING header allows arbitrary file reads through nginx

Description (CNA)

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 (CNA)

Vendor / product	Versions
rack / rack	affected < 2.2.23; affected >= 3.0.0.beta1, < 3.1.21; affected >= 3.2.0, < 3.2.6

CWE

CWE-625

References

https://github.com/rack/rack/security/advisories/GHSA-qv7j-4883-hwh7

ADP enrichment

CISA-ADP

No English description supplied.

No references supplied.