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Rack: Rack::Sendfile regex injection via HTTP_X_ACCEL_MAPPING header allows arbitrary file reads through nginx

F5 NGINX · CVE-2026-34830
0 news outlets0 CERTs and agencies0 researchers

Assessment: Track

SSVC decision points: exploitation none, automatable no, technical impact partial, deployment medium.

What is it?

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.

Evidence

No coverage recorded yet.

Exploitation

  • Public proof of concept
  • Exploited in the wild
  • Listed as known exploited
CVSS
5.9
EPSS
0.4%
First seen
2 d ago
Status
corroborated

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