GHSA-x8cg-fq8g-mxfx CVE-2026-34826
Rack's multipart byte range processing allows denial of service via excessive overlapping ranges
- Severity
- 5.3 / 10
- High · CVSS 3.1
- Exploit chance (EPSS)
- 0.40%
- Chance of exploitation in the next 30 days. Higher than 33.75% of scored vulnerabilities.
- Known exploited
- No
- Not in CISA's catalog
- Weakness
- CWE-400 Uncontrolled Resource Consumption
- CWE-770 Allocation of Resources Without Limits or Throttling
- Fix
2.2.23- Upgrade rack to this version or later
Description
Summary
Rack::Utils.get_byte_ranges parses the HTTP Range header without limiting the number of individual byte ranges. Although the existing fix for CVE-2024-26141 rejects ranges whose total byte coverage exceeds the file size, it does not restrict the count of ranges. An attacker can supply many small overlapping ranges such as 0-0,0-0,0-0,... to trigger disproportionate CPU, memory, I/O, and bandwidth consumption per request.
This results in a denial of service condition in Rack file-serving paths that process multipart byte range responses.
Details
Rack::Utils.get_byte_ranges accepts a comma-separated list of byte ranges and validates them based on their aggregate size, but does not impose a limit on how many individual ranges may be supplied.
As a result, a request such as:
Range: bytes=0-0,0-0,0-0,0-0,...
can contain thousands of overlapping one-byte ranges while still satisfying the total-size check added for CVE-2024-26141.
When such a header is processed by Rack’s file-serving code, each range causes additional work, including multipart response generation, per-range iteration, file seek and read operations, and temporary string allocation for response size calculation and output. This allows a relatively small request header to trigger disproportionately expensive processing and a much larger multipart response.
The issue is distinct from CVE-2024-26141. That fix prevents range sets whose total byte coverage exceeds the file size, but does not prevent a large number of overlapping ranges whose summed size remains within that limit.
Impact
Applications that expose file-serving paths with byte range support may be vulnerable to denial of service.
An unauthenticated attacker can send crafted Range headers containing many small overlapping ranges to consume excessive CPU time, memory, file I/O, and bandwidth. Repeated requests may reduce application availability and increase pressure on workers and garbage collection.
Mitigation
- Update to a patched version of Rack that limits the number of accepted byte ranges.
- Reject or normalize multipart byte range requests containing excessive range counts.
- Consider disabling multipart range support where it is not required.
- Apply request filtering or header restrictions at the reverse proxy or application boundary to limit abusive
Rangeheaders.
Affected versions
RubyGems
| Package | Vulnerable | Fixed in |
|---|---|---|
| rack | < 2.2.23 |
2.2.23 |
| rack | >= 3.0.0.beta1, < 3.1.21 |
3.1.21 |
| rack | >= 3.2.0, < 3.2.6 |
3.2.6 |
How to fix
Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.
rack RubyGems → 2.2.23
- bundler
bundle update rack # Gemfile: gem "rack", ">= 2.2.23"
Severity breakdown
CVSS 3.1 5.3
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- None
- Availability
- Low
Weakness
CWE-400: Uncontrolled Resource Consumption
The product does not properly control the allocation and maintenance of a limited resource.
How to prevent it
- Architecture and Design: Design throttling mechanisms into the system architecture. The best protection is to limit the amount of resources that an unauthorized user can cause to be expended. A strong authentication and access control model will help prevent such attacks from occurring in the first place. The login application should be protected against DoS attacks as much as possible. Limiting the database access, perhaps by caching result sets, can help minimize the resources expended. To further limit the potential for a DoS attack, consider tracking the rate of requests received from users and blocking requests that exceed a defined rate threshold.
- Architecture and Design: Mitigation of resource exhaustion attacks requires that the target system either: recognizes the attack and denies that user further access for a given amount of time, or uniformly throttles all requests in order to make it more difficult to consume resources more quickly than they can again be freed. The first of these solutions is an issue in itself though, since it may allow attackers to prevent the use of the system by a particular valid user. If the attacker impersonates the valid user, they may be able to prevent the user from accessing the server in question. The second solution is simply difficult to effectively institute -- and even when properly done, it does not provide a full solution. It simply makes the attack require more resources on the part of the attacker.
- Architecture and Design: Ensure that protocols have specific limits of scale placed on them.
- Implementation: Ensure that all failures in resource allocation place the system into a safe posture.
CWE-770: Allocation of Resources Without Limits or Throttling
The product allocates a reusable resource or group of resources on behalf of an actor without imposing any intended restrictions on the size or number of resources that can be allocated.
How to prevent it
- Requirements: Clearly specify the minimum and maximum expectations for capabilities, and dictate which behaviors are acceptable when resource allocation reaches limits.
- Architecture and Design: Limit the amount of resources that are accessible to unprivileged users. Set per-user limits for resources. Allow the system administrator to define these limits. Be careful to avoid CWE-410.
- Architecture and Design: Design throttling mechanisms into the system architecture. The best protection is to limit the amount of resources that an unauthorized user can cause to be expended. A strong authentication and access control model will help prevent such attacks from occurring in the first place, and it will help the administrator to identify who is committing the abuse. The login application should be protected against DoS attacks as much as possible. Limiting the database access, perhaps by caching result sets, can help minimize the resources expended. To further limit the potential for a DoS attack, consider tracking the rate of requests received from users and blocking requests that exceed a defined rate threshold.
- Implementation: Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does. When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as "red" or "blue." Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.
- Architecture and Design: For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side, in order to avoid CWE-602. Attackers can bypass the client-side checks by modifying values after the checks have been performed, or by changing the client to remove the client-side checks entirely. Then, these modified values would be submitted to the server.
- Architecture and Design: Mitigation of resource exhaustion attacks requires that the target system either: recognizes the attack and denies that user further access for a given amount of time, typically by using increasing time delays uniformly throttles all requests in order to make it more difficult to consume resources more quickly than they can again be freed. The first of these solutions is an issue in itself though, since it may allow attackers to prevent the use of the system by a particular valid user. If the attacker impersonates the valid user, they may be able to prevent the user from accessing the server in question. The second solution can be difficult to effectively institute -- and even when properly done, it does not provide a full solution. It simply requires more resources on the part of the attacker.
- Architecture and Design: Ensure that protocols have specific limits of scale placed on them.
- Architecture and Design, Implementation: If the program must fail, ensure that it fails gracefully (fails closed). There may be a temptation to simply let the program fail poorly in cases such as low memory conditions, but an attacker may be able to assert control before the software has fully exited. Alternately, an uncontrolled failure could cause cascading problems with other downstream components; for example, the program could send a signal to a downstream process so the process immediately knows that a problem has occurred and has a better chance of recovery. Ensure that all failures in resource allocation place the system into a safe posture.
- Operation, Architecture and Design: Use quotas or other resource-limiting settings provided by the operating system or environment. For example, when managing system resources in POSIX, setrlimit() can be used to set limits for certain types of resources, and getrlimit() can determine how many resources are available. However, these functions are not available on all operating systems. When the current levels get close to the maximum that is defined for the application (see CWE-770), then limit the allocation of further resources to privileged users; alternately, begin releasing resources for less-privileged users. While this mitigation may protect the system from attack, it will not necessarily stop attackers from adversely impacting other users. Ensure that the application performs the appropriate error checks and error handling in case resources become unavailable (CWE-703).
References
Advisories
Packages
Other links
Timeline
- Published
- Last updated by the source
- Latest EPSS score
Related advisories
| Advisory | Severity | Why it's related |
|---|---|---|
| GHSA-g2pf-xv49-m2h5 Rack::Request accepts invalid Host characters, enabling host allowlist bypass | Medium | Also affects rack |
| GHSA-v6x5-cg8r-vv6x Rack's multipart header parsing allows Denial of Service via escape-heavy quoted parameters | High | Also affects rack |
| GHSA-qfgr-crr9-7r49 Rack: Forwarded Header semicolon injection enables Host and Scheme spoofing | Medium | Also affects rack |
| GHSA-rx22-g9mx-qrhv Rack's improper unfolding of folded multipart headers preserves CRLF in parsed parameter values | Medium | Also affects rack |
| GHSA-q2ww-5357-x388 Rack has Content-Length mismatch in Rack::Files error responses | Medium | Also affects rack |
| GHSA-qv7j-4883-hwh7 Rack::Sendfile header-based X-Accel-Mapping regex injection enables unauthorized X-Accel-Redirect | High | Also affects rack |
| GHSA-8vqr-qjwx-82mw Rack's multipart parsing without Content-Length header allows unbounded chunked file uploads | High | Also affects rack |
| GHSA-q4qf-9j86-f5mh Rack:: Static header_rules bypass via URL-encoded paths | Medium | Also affects rack |
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