CVE-2026-34785: rack Partial String Comparison

Vulnerability summary

CVE-2026-34785 is a high (CVSS 7.5) Partial String Comparison vulnerability in rack. EPSS estimates a 0.52% chance of exploitation in the next 30 days, higher than 42.8% of scored vulnerabilities.

Timeline

1. 02-04-2026
   PublishedVulnerability first disclosed.
2. 15-07-2026
   Last modifiedVulnerability information updated.

Description

Rack is a modular Ruby web server interface. Prior to versions 2.2.23, 3.1.21, and 3.2.6, Rack::Static determines whether a request should be served as a static file using a simple string prefix check. When configured with URL prefixes such as "/css", it matches any request path that begins with that string, including unrelated paths such as "/css-config.env" or "/css-backup.sql". As a result, files under the static root whose names merely share the configured prefix may be served unintentionally, leading to information disclosure. This issue has been patched in versions 2.2.23, 3.1.21, and 3.2.6.

• CWE-187Partial String ComparisonThe product performs a comparison that only examines a portion of a factor before determining whether there is a match, such as a substring, leading to resultant weaknesses.
• CWE-200Exposure of Sensitive Information to an Unauthorized ActorThe product exposes sensitive information to an actor that is not explicitly authorized to have access to that information.
• CWE-552Files or Directories Accessible to External PartiesThe product makes files or directories accessible to unauthorized actors, even though they should not be.