A DoS vulnerability exists in Rack <v3.0.4.2, <v2.2.6.3, <v2.1.4.3 and <v2.0.9.3 within in the Multipart MIME parsing code in which could allow an attacker to craft requests that can be abuse to cause multipart parsing to take longer than expected.

Carefully crafted input can cause Content-Disposition header parsing in Rack to take an unexpected amount of time, possibly resulting in a denial of service attack vector. This header is used typically used in multipart parsing. Any applications that parse multipart posts using Rack (virtually all Rails applications) are impacted.

A denial of service vulnerability in the Range header parsing component of Rack >= 1.5.0. A Carefully crafted input can cause the Range header parsing component in Rack to take an unexpected amount of time, possibly resulting in a denial of service attack vector. Any applications that deal with Range requests (such as streaming applications, or applications that serve files) may be impacted.

A denial of service vulnerability in the multipart parsing component of Rack fixed in 2.0.9.2, 2.1.4.2, 2.2.4.1 and 3.0.0.1 could allow an attacker tocraft input that can cause RFC2183 multipart boundary parsing in Rack to take an unexpected amount of time, possibly resulting in a denial of service attack vector. Any applications that parse multipart posts using Rack (virtually all Rails applications) are impacted.

A denial of service flaw was found in ruby-rack. An attacker crafting multipart POST requests can cause Rack's multipart parser to take much longer than expected, leading to a denial of service.

A flaw was found in ruby gem-rack. This flaw allows a malicious actor to craft requests that can cause shell escape sequences to be written to the terminal via rack's Lint middleware and CommonLogger middleware. This issue can leverage these escape sequences to execute commands in the victim's terminal.

A flaw was found in rubygem-rack. An attacker may be able to trick a vulnerable application into processing an insecure (non-SSL) or cross-origin request if they can gain the ability to write arbitrary cookies that are sent to the application. The highest threat from this vulnerability is to data integrity.

A directory traversal vulnerability exists in rack < 2.2.0 that allows an attacker perform directory traversal vulnerability in the Rack::Directory app that is bundled with Rack which could result in information disclosure.

A flaw was found in rubygem-rack in versions prior to 1.6.12 and 2.0.8. An information leak may allow an attacker to find and hijack sessions using timing attacks targeting the session ID. The highest threat from the vulnerability is to data confidentiality.

Last updated 25 August 2025

Rack (rubygem-rack) versions 2.04 and 2.0.5 are vulnerable to a denial of service due to incorrect buffer size in the multipart parser. Carefully crafted requests can cause the multipart parser to enter a pathological state, causing the parser to use CPU resources disproportionate to the request size.

External Reference:

https://groups.google.com/forum/#!msg/rubyonrails-security/Ux-YkfuVTg/xhvYAmp6AAAJ

lib/rack/utils.rb in Rack before 1.5.4 and 1.6.x before 1.6.2, as used with Ruby on Rails 3.x and 4.x and other products, allows remote attackers to cause a denial of service (SystemStackError) via a request with a large parameter depth.

rack/file.rb (Rack::File) in Rack 1.5.x before 1.5.2 and 1.4.x before 1.4.5 allows attackers to access arbitrary files outside the intended root directory via a crafted PATHINFO environment variable, probably a directory traversal vulnerability that is remotely exploitable, aka "symlink path traversals."

James Tucker (raggi) reports:

CVE: CVE-2013-0263 Software: Rack (rack.github.com) Type of vulnerability: Timing attack, leading to potential RCE

Vulnerable code: https://github.com/rack/rack/blob/master/lib/rack/session/cookie.rb#L149 Patch: https://github.com/rack/rack/commit/0cd7e9aa397f8ebb3b8481d67dbac8b4863a7f07 https://github.com/rack/rack/commit/9a81b961457805f6d1a5c275d053068440421e11

Versions affected: All prior versions. Versions fixed: 1.1.6, 1.2.8, 1.3.10, 1.4.5, 1.5.2 Reporter: Ben Murphy

Reference: http://seclists.org/oss-sec/2013/q1/271

A flaw that was fixed in 1.4.4, 1.3.9, 1.2.7, and 1.1.5 was also announced [4] that creates a minor denial of service condition, this time in the Rack::Auth::AbstractRequest, where it symbolized arbitrary strings (apparently this has something to do with authentication, but there is no further information provided other than the fix [5] itself, which is noted as "a breaking API change").

[4] https://groups.google.com/forum/#!topic/rack-devel/ImYOqcGiksw/discussion [5] https://github.com/rack/rack/commit/0c76175fcccad74ba2f991c487d3669c28a297c8

multipart/parser.rb in Rack 1.3.x before 1.3.8 and 1.4.x before 1.4.3 allows remote attackers to cause a denial of service (memory consumption and out-of-memory error) via a long string in a Multipart HTTP packet.

lib/rack/multipart.rb in Rack before 1.1.4, 1.2.x before 1.2.6, 1.3.x before 1.3.7, and 1.4.x before 1.4.2 uses an incorrect regular expression, which allows remote attackers to cause a denial of service (infinite loop) via a crafted Content-Disposion header.

Rack before 1.1.3, 1.2.x before 1.2.5, and 1.3.x before 1.3.6 computes hash values for form parameters without restricting the ability to trigger hash collisions predictably, which allows remote attackers to cause a denial of service (CPU consumption) by sending many crafted parameters.