🚨 [security] [ruby] Update rack 2.2.6.4 → 2.2.20 (minor) #421

depfu · 2025-10-10T18:13:10Z

🚨 Your current dependencies have known security vulnerabilities 🚨

This dependency update fixes known security vulnerabilities. Please see the details below and assess their impact carefully. We recommend to merge and deploy this as soon as possible!

Here is everything you need to know about this update. Please take a good look at what changed and the test results before merging this pull request.

What changed?

↗️ rack (indirect, 2.2.6.4 → 2.2.20) · Repo · Changelog

Security Advisories 🚨

🚨 Rack is vulnerable to a memory-exhaustion DoS through unbounded URL-encoded body parsing

Summary

Rack::Request#POST reads the entire request body into memory for Content-Type: application/x-www-form-urlencoded, calling rack.input.read(nil) without enforcing a length or cap. Large request bodies can therefore be buffered completely into process memory before parsing, leading to denial of service (DoS) through memory exhaustion.

Details

When handling non-multipart form submissions, Rack’s request parser performs:
form_vars = get_header(RACK_INPUT).read
Since read is called with no argument, the entire request body is loaded into a Ruby String. This occurs before query parameter parsing or enforcement of any params_limit. As a result, Rack applications without an upstream body-size limit can experience unbounded memory allocation proportional to request size.

Impact

Attackers can send large application/x-www-form-urlencoded bodies to consume process memory, causing slowdowns or termination by the operating system (OOM). The effect scales linearly with request size and concurrency. Even with parsing limits configured, the issue occurs before those limits are enforced.

Mitigation

Update to a patched version of Rack that enforces form parameter limits using query_parser.bytesize_limit, preventing unbounded reads of application/x-www-form-urlencoded bodies.

Enforce strict maximum body size at the proxy or web server layer (e.g., Nginx client_max_body_size, Apache LimitRequestBody).

🚨 Rack has a Possible Information Disclosure Vulnerability

Summary

A possible information disclosure vulnerability existed in Rack::Sendfile when running behind a proxy that supports x-sendfile headers (such as Nginx). Specially crafted headers could cause Rack::Sendfile to miscommunicate with the proxy and trigger unintended internal requests, potentially bypassing proxy-level access restrictions.

Details

When Rack::Sendfile received untrusted x-sendfile-type or x-accel-mapping headers from a client, it would interpret them as proxy configuration directives. This could cause the middleware to send a "redirect" response to the proxy, prompting it to reissue a new internal request that was not subject to the proxy's access controls.

An attacker could exploit this by:

Setting a crafted x-sendfile-type: x-accel-redirect header.

Setting a crafted x-accel-mapping header.

Requesting a path that qualifies for proxy-based acceleration.

Impact

Attackers could bypass proxy-enforced restrictions and access internal endpoints intended to be protected (such as administrative pages). The vulnerability did not allow arbitrary file reads but could expose sensitive application routes.

This issue only affected systems meeting all of the following conditions:

The application used Rack::Sendfile with a proxy that supports x-accel-redirect (e.g., Nginx).

The proxy did not always set or remove the x-sendfile-type and x-accel-mapping headers.

The application exposed an endpoint that returned a body responding to .to_path.

Mitigation
Upgrade to a fixed version of Rack which requires explicit configuration to enable x-accel-redirect:
use Rack::Sendfile, "x-accel-redirect"
Alternatively, configure the proxy to always set or strip the headers (you should be doing this!):
proxy_set_header x-sendfile-type x-accel-redirect;
proxy_set_header x-accel-mapping /var/www/=/files/;
Or in Rails applications, disable sendfile completely:
config.action_dispatch.x_sendfile_header = nil

🚨 Rack's multipart parser buffers unbounded per-part headers, enabling DoS (memory exhaustion)

Summary

Rack::Multipart::Parser can accumulate unbounded data when a multipart part’s header block never terminates with the required blank line (CRLFCRLF). The parser keeps appending incoming bytes to memory without a size cap, allowing a remote attacker to exhaust memory and cause a denial of service (DoS).

Details

While reading multipart headers, the parser waits for CRLFCRLF using:
@sbuf.scan_until(/(.*?\r\n)\r\n/m)
If the terminator never appears, it continues appending data (@sbuf.concat(content)) indefinitely. There is no limit on accumulated header bytes, so a single malformed part can consume memory proportional to the request body size.

Impact

Attackers can send incomplete multipart headers to trigger high memory use, leading to process termination (OOM) or severe slowdown. The effect scales with request size limits and concurrency. All applications handling multipart uploads may be affected.

Mitigation

Upgrade to a patched Rack version that caps per-part header size (e.g., 64 KiB).

Until then, restrict maximum request sizes at the proxy or web server layer (e.g., Nginx client_max_body_size).

🚨 Rack: Multipart parser buffers large non‑file fields entirely in memory, enabling DoS (memory exhaustion)

Summary

Rack::Multipart::Parser stores non-file form fields (parts without a filename) entirely in memory as Ruby String objects. A single large text field in a multipart/form-data request (hundreds of megabytes or more) can consume equivalent process memory, potentially leading to out-of-memory (OOM) conditions and denial of service (DoS).

Details

During multipart parsing, file parts are streamed to temporary files, but non-file parts are buffered into memory:
body = String.new  # non-file → in-RAM buffer
@mime_parts[mime_index].body << content
There is no size limit on these in-memory buffers. As a result, any large text field—while technically valid—will be loaded fully into process memory before being added to params.

Impact

Attackers can send large non-file fields to trigger excessive memory usage. Impact scales with request size and concurrency, potentially leading to worker crashes or severe garbage-collection overhead. All Rack applications processing multipart form submissions are affected.

Mitigation

Upgrade: Use a patched version of Rack that enforces a reasonable size cap for non-file fields (e.g., 2 MiB).

Workarounds:

Restrict maximum request body size at the web-server or proxy layer (e.g., Nginx client_max_body_size).

Validate and reject unusually large form fields at the application level.

🚨 Rack's unbounded multipart preamble buffering enables DoS (memory exhaustion)

Summary

Rack::Multipart::Parser buffers the entire multipart preamble (bytes before the first boundary) in memory without any size limit. A client can send a large preamble followed by a valid boundary, causing significant memory use and potential process termination due to out-of-memory (OOM) conditions.

Details

While searching for the first boundary, the parser appends incoming data into a shared buffer (@sbuf.concat(content)) and scans for the boundary pattern:
@sbuf.scan_until(@body_regex)
If the boundary is not yet found, the parser continues buffering data indefinitely. There is no trimming or size cap on the preamble, allowing attackers to send arbitrary amounts of data before the first boundary.

Impact

Remote attackers can trigger large transient memory spikes by including a long preamble in multipart/form-data requests. The impact scales with allowed request sizes and concurrency, potentially causing worker crashes or severe slowdown due to garbage collection.

Mitigation

Upgrade: Use a patched version of Rack that enforces a preamble size limit (e.g., 16 KiB) or discards preamble data entirely per RFC 2046 § 5.1.1.

Workarounds:

Limit total request body size at the proxy or web server level.

Monitor memory and set per-process limits to prevent OOM conditions.

🚨 Rack has an unsafe default in Rack::QueryParser allows params_limit bypass via semicolon-separated parameters

Summary

Rack::QueryParser in version < 2.2.18 enforces its params_limit only for parameters separated by &, while still splitting on both & and ;. As a result, attackers could use ; separators to bypass the parameter count limit and submit more parameters than intended.

Details

The issue arises because Rack::QueryParser#check_query_string counts only & characters when determining the number of parameters, but the default separator regex DEFAULT_SEP = /[&;] */n splits on both & and ;. This mismatch means that queries using ; separators were not included in the parameter count, allowing params_limit to be bypassed.

Other safeguards (bytesize_limit and key_space_limit) still applied, but did not prevent this particular bypass.

Impact

Applications or middleware that directly invoke Rack::QueryParser with its default configuration (no explicit delimiter) could be exposed to increased CPU and memory consumption. This can be abused as a limited denial-of-service vector.

Rack::Request, the primary entry point for typical Rack applications, uses QueryParser in a safe way and does not appear vulnerable by default. As such, the severity is considered low, with the impact limited to edge cases where QueryParser is used directly.

Mitigation

Upgrade to a patched version of Rack where both & and ; are counted consistently toward params_limit.

If upgrading is not immediately possible, configure QueryParser with an explicit delimiter (e.g., &) to avoid the mismatch.

As a general precaution, enforce query string and request size limits at the web server or proxy layer (e.g., Nginx, Apache, or a CDN) to mitigate excessive parsing overhead.

🚨 Rack has an Unbounded-Parameter DoS in Rack::QueryParser

Summary

Rack::QueryParser parses query strings and application/x-www-form-urlencoded bodies into Ruby data structures without imposing any limit on the number of parameters, allowing attackers to send requests with extremely large numbers of parameters.

Details

The vulnerability arises because Rack::QueryParser iterates over each &-separated key-value pair and adds it to a Hash without enforcing an upper bound on the total number of parameters. This allows an attacker to send a single request containing hundreds of thousands (or more) of parameters, which consumes excessive memory and CPU during parsing.

Impact

An attacker can trigger denial of service by sending specifically crafted HTTP requests, which can cause memory exhaustion or pin CPU resources, stalling or crashing the Rack server. This results in full service disruption until the affected worker is restarted.

Mitigation

Update to a version of Rack that limits the number of parameters parsed, or

Use middleware to enforce a maximum query string size or parameter count, or

Employ a reverse proxy (such as Nginx) to limit request sizes and reject oversized query strings or bodies.

Limiting request body sizes and query string lengths at the web server or CDN level is an effective mitigation.

🚨 Rack session gets restored after deletion

Summary

When using the Rack::Session::Pool middleware, simultaneous rack requests can restore a deleted rack session, which allows the unauthenticated user to occupy that session.

Details

Rack session middleware prepares the session at the beginning of request, then saves is back to the store with possible changes applied by host rack application. This way the session becomes to be a subject of race conditions in general sense over concurrent rack requests.

Impact

When using the Rack::Session::Pool middleware, and provided the attacker can acquire a session cookie (already a major issue), the session may be restored if the attacker can trigger a long running request (within that same session) adjacent to the user logging out, in order to retain illicit access even after a user has attempted to logout.

Mitigation

Update to the latest version of rack, or

Ensure your application invalidates sessions atomically by marking them as logged out e.g., using a logged_out flag, instead of deleting them, and check this flag on every request to prevent reuse, or

Implement a custom session store that tracks session invalidation timestamps and refuses to accept session data if the session was invalidated after the request began.

Related

As this code was moved to rack-session in Rack 3+, see GHSA-9j94-67jr-4cqj for the equivalent advisory in rack-session (affecting Rack 3+ only).

🚨 Local File Inclusion in Rack::Static

Summary

Rack::Static can serve files under the specified root: even if urls: are provided, which may expose other files under the specified root: unexpectedly.

Details

The vulnerability occurs because Rack::Static does not properly sanitize user-supplied paths before serving files. Specifically, encoded path traversal sequences are not correctly validated, allowing attackers to access files outside the designated static file directory.

Impact

By exploiting this vulnerability, an attacker can gain access to all files under the specified root: directory, provided they are able to determine then path of the file.

Mitigation

Update to the latest version of Rack, or

Remove usage of Rack::Static, or

Ensure that root: points at a directory path which only contains files which should be accessed publicly.

It is likely that a CDN or similar static file server would also mitigate the issue.

🚨 Escape Sequence Injection vulnerability in Rack lead to Possible Log Injection

Summary

Rack::Sendfile can be exploited by crafting input that includes newline characters to manipulate log entries.

Details

The Rack::Sendfile middleware logs unsanitized header values from the X-Sendfile-Type header. An attacker can exploit this by injecting escape sequences (such as newline characters) into the header, resulting in log injection.

Impact

This vulnerability can distort log files, obscure attack traces, and complicate security auditing.

Mitigation

Update to the latest version of Rack, or

Remove usage of Rack::Sendfile.

🚨 Possible Log Injection in Rack::CommonLogger

Summary

Rack::CommonLogger can be exploited by crafting input that includes newline characters to manipulate log entries. The supplied proof-of-concept demonstrates injecting malicious content into logs.

Details

When a user provides the authorization credentials via Rack::Auth::Basic, if success, the username will be put in env['REMOTE_USER'] and later be used by Rack::CommonLogger for logging purposes.

The issue occurs when a server intentionally or unintentionally allows a user creation with the username contain CRLF and white space characters, or the server just want to log every login attempts. If an attacker enters a username with CRLF character, the logger will log the malicious username with CRLF characters into the logfile.

Impact

Attackers can break log formats or insert fraudulent entries, potentially obscuring real activity or injecting malicious data into log files.

Mitigation

Update to the latest version of Rack.

🚨 Rack vulnerable to ReDoS in content type parsing (2nd degree polynomial)

Summary
module Rack
  class MediaType
    SPLIT_PATTERN = %r{\s*[;,]\s*}
The above regexp is subject to ReDos. 50K blank characters as a prefix to the header will take over 10s to split.

PoC

A simple HTTP request with lots of blank characters in the content-type header:
request["Content-Type"] = (" " * 50_000) + "a,"
Impact

It's a very easy to craft ReDoS. Like all ReDoS the impact is debatable.

🚨 Rack Header Parsing leads to Possible Denial of Service Vulnerability

Possible Denial of Service Vulnerability in Rack Header Parsing

There is a possible denial of service vulnerability in the header parsing
routines in Rack. This vulnerability has been assigned the CVE identifier
CVE-2024-26146.

Versions Affected: All.
Not affected: None
Fixed Versions: 2.0.9.4, 2.1.4.4, 2.2.8.1, 3.0.9.1

Impact

Carefully crafted headers can cause header parsing in Rack to take longer than
expected resulting in a possible denial of service issue. Accept and Forwarded
headers are impacted.

Ruby 3.2 has mitigations for this problem, so Rack applications using Ruby 3.2
or newer are unaffected.

Releases

The fixed releases are available at the normal locations.

Workarounds

There are no feasible workarounds for this issue.

Patches

To aid users who aren't able to upgrade immediately we have provided patches for
the two supported release series. They are in git-am format and consist of a
single changeset.

2-0-header-redos.patch - Patch for 2.0 series

2-1-header-redos.patch - Patch for 2.1 series

2-2-header-redos.patch - Patch for 2.2 series

3-0-header-redos.patch - Patch for 3.0 series

Credits

Thanks to svalkanov for reporting this and
providing patches!

🚨 Rack has possible DoS Vulnerability with Range Header

Possible DoS Vulnerability with Range Header in Rack

There is a possible DoS vulnerability relating to the Range request header in
Rack. This vulnerability has been assigned the CVE identifier CVE-2024-26141.

Versions Affected: >= 1.3.0.
Not affected: < 1.3.0
Fixed Versions: 3.0.9.1, 2.2.8.1

Impact

Carefully crafted Range headers can cause a server to respond with an
unexpectedly large response. Responding with such large responses could lead
to a denial of service issue.

Vulnerable applications will use the Rack::File middleware or the
Rack::Utils.byte_ranges methods (this includes Rails applications).

Releases

The fixed releases are available at the normal locations.

Workarounds

There are no feasible workarounds for this issue.

Patches

To aid users who aren't able to upgrade immediately we have provided patches for
the two supported release series. They are in git-am format and consist of a
single changeset.

3-0-range.patch - Patch for 3.0 series

2-2-range.patch - Patch for 2.2 series

Credits

Thank you ooooooo_q for the report and
patch

Release Notes

2.2.19 (from changelog)

Security

CVE-2025-61772 Multipart parser buffers unbounded per-part headers, enabling DoS (memory exhaustion)

CVE-2025-61771 Multipart parser buffers large non‑file fields entirely in memory, enabling DoS (memory exhaustion)

CVE-2025-61770 Unbounded multipart preamble buffering enables DoS (memory exhaustion)

2.2.16 (from changelog)

Fix incorrect backport of optional CGI::Cookie support. (#2335, @jeremyevans)

2.2.15 (from changelog)

Optional support for CGI::Cookie if not available. (#2327, #2333, @earlopain)

2.2.14 (from changelog)

Security

CVE-2025-46727 Unbounded parameter parsing in Rack::QueryParser can lead to memory exhaustion.

2.2.13 (from changelog)

Security

CVE-2025-27610 Local file inclusion in Rack::Static.

2.2.12 (from changelog)

Security

CVE-2025-27111 Possible Log Injection in Rack::Sendfile.

2.2.10 (from changelog)

Fix compatibility issues with Ruby v3.4.0. (#2248, @byroot)

2.2.8.1

What's Changed

Fixed ReDoS in Accept header parsing [CVE-2024-26146]

Fixed ReDoS in Content Type header parsing [CVE-2024-25126]

Reject Range headers which are too large [CVE-2024-26141]

Full Changelog: v2.2.8...v2.2.8.1

2.2.7

What's Changed

Correct the year number in the changelog by @kimulab in #2015

Support underscore in host names for Rack 2.2 (Fixes #2070) by @jeremyevans in #2071

New Contributors

@kimulab made their first contribution in #2015

Full Changelog: v2.2.6.4...v2.2.7

Does any of this look wrong? Please let us know.

Commits

See the full diff on Github. The new version differs by 52 commits:

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Update rack to version 2.2.20

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🚨 [security] [ruby] Update rack 2.2.6.4 → 2.2.19 (minor) #420

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🚨 [security] [ruby] Update rack 2.2.6.4 → 2.2.20 (minor) #421

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What changed?

↗️ rack (indirect, 2.2.6.4 → 2.2.20) · Repo · Changelog

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Possible Denial of Service Vulnerability in Rack Header Parsing

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Possible DoS Vulnerability with Range Header in Rack

Impact

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Credits

2.2.19 (from changelog)

Security

2.2.16 (from changelog)

2.2.15 (from changelog)

2.2.14 (from changelog)

Security

2.2.13 (from changelog)

Security

2.2.12 (from changelog)

Security

2.2.10 (from changelog)

What's Changed