GHSA-m42x-37p3-fv5w CVE-2020-8162
Circumvention of file size limits in ActiveStorage
High
RubyGems
- Severity
- 7.5 / 10
- High · CVSS 3.1
- Exploit chance (EPSS)
- 3.03%
- Chance of exploitation in the next 30 days. Higher than 87.48% of scored vulnerabilities.
- Known exploited
- No
- Not in CISA's catalog
- Weakness
- CWE-434 Unrestricted Upload of File with Dangerous Type
- CWE-602 Client-Side Enforcement of Server-Side Security
- Fix
5.2.4.3- Upgrade activestorage to this version or later
Description
There is a vulnerability in ActiveStorage's S3 adapter that allows the Content-Length of a direct file upload to be modified by an end user.
Versions Affected: rails < 5.2.4.2, rails < 6.0.3.1 Not affected: Applications that do not use the direct upload functionality of the ActiveStorage S3 adapter. Fixed Versions: rails >= 5.2.4.3, rails >= 6.0.3.1
Impact
Utilizing this vulnerability, an attacker can control the Content-Length of an S3 direct upload URL without receiving a new signature from the server. This could be used to bypass controls in place on the server to limit upload size.
Workarounds
This is a low-severity security issue. As such, no workaround is necessarily until such time as the application can be upgraded.
Affected versions
RubyGems
| Package | Vulnerable | Fixed in |
|---|---|---|
| activestorage | >= 5.0.0, < 5.2.4.3 |
5.2.4.3 |
| activestorage | >= 6.0.0, < 6.0.3.1 |
6.0.3.1 |
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.
activestorage RubyGems → 5.2.4.3
- bundler
bundle update activestorage # Gemfile: gem "activestorage", ">= 5.2.4.3"
Severity breakdown
CVSS 3.1 7.5
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- High
- Availability
- None
Weakness
CWE-434: Unrestricted Upload of File with Dangerous Type
The product allows the upload or transfer of dangerous file types that are automatically processed within its environment.
How to prevent it
- Architecture and Design: Generate a new, unique filename for an uploaded file instead of using the user-supplied filename, so that no external input is used at all.[REF-422] [REF-423]
- Architecture and Design: When the set of acceptable objects, such as filenames or URLs, is limited or known, create a mapping from a set of fixed input values (such as numeric IDs) to the actual filenames or URLs, and reject all other inputs.
- Architecture and Design: Consider storing the uploaded files outside of the web document root entirely. Then, use other mechanisms to deliver the files dynamically. [REF-423]
- 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. For example, limiting filenames to alphanumeric characters can help to restrict the introduction of unintended file extensions.
- Architecture and Design: Define a very limited set of allowable extensions and only generate filenames that end in these extensions. Consider the possibility of XSS (CWE-79) before allowing .html or .htm file types.
- Implementation: Ensure that only one extension is used in the filename. Some web servers, including some versions of Apache, may process files based on inner extensions so that "filename.php.gif" is fed to the PHP interpreter.[REF-422] [REF-423]
- Implementation: When running on a web server that supports case-insensitive filenames, perform case-insensitive evaluations of the extensions that are provided.
- 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.
- Implementation: Do not rely exclusively on sanity checks of file contents to ensure that the file is of the expected type and size. It may be possible for an attacker to hide code in some file segments that will still be executed by the server. For example, GIF images may contain a free-form comments field.
- Implementation: Do not rely exclusively on the MIME content type or filename attribute when determining how to render a file. Validating the MIME content type and ensuring that it matches the extension is only a partial solution.
- Architecture and Design, Operation: Run your code using the lowest privileges that are required to accomplish the necessary tasks [REF-76]. If possible, create isolated accounts with limited privileges that are only used for a single task. That way, a successful attack will not immediately give the attacker access to the rest of the software or its environment. For example, database applications rarely need to run as the database administrator, especially in day-to-day operations.
- Architecture and Design, Operation: Run the code in a "jail" or similar sandbox environment that enforces strict boundaries between the process and the operating system. This may effectively restrict which files can be accessed in a particular directory or which commands can be executed by the software. OS-level examples include the Unix chroot jail, AppArmor, and SELinux. In general, managed code may provide some protection. For example, java.io.FilePermission in the Java SecurityManager allows the software to specify restrictions on file operations. This may not be a feasible solution, and it only limits the impact to the operating system; the rest of the application may still be subject to compromise. Be careful to avoid CWE-243 and other weaknesses related to jails.
CWE-602: Client-Side Enforcement of Server-Side Security
The product is composed of a server that relies on the client to implement a mechanism that is intended to protect the server.
How to prevent it
- Architecture and Design: For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side. 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. Even though client-side checks provide minimal benefits with respect to server-side security, they are still useful. First, they can support intrusion detection. If the server receives input that should have been rejected by the client, then it may be an indication of an attack. Second, client-side error-checking can provide helpful feedback to the user about the expectations for valid input. Third, there may be a reduction in server-side processing time for accidental input errors, although this is typically a small savings.
- Architecture and Design: If some degree of trust is required between the two entities, then use integrity checking and strong authentication to ensure that the inputs are coming from a trusted source. Design the product so that this trust is managed in a centralized fashion, especially if there are complex or numerous communication channels, in order to reduce the risks that the implementer will mistakenly omit a check in a single code path.
References
Advisories
Other links
Timeline
- Published
- Last updated by the source
- Latest EPSS score
Related advisories
| Advisory | Severity | Why it's related |
|---|---|---|
| GHSA-xr9x-r78c-5hrm Active Storage has possible arbitrary file read and remote code execution in Active Storage variant processing | Critical | Also affects activestorage |
| GHSA-p9fm-f462-ggrg Rails Active Storage has a possible DoS vulnerability in proxy mode via multi-range requests | Medium | Also affects activestorage |
| GHSA-73f9-jhhh-hr5m Rails Active Storage has possible glob injection in its DiskService | Critical | Also affects activestorage |
| GHSA-9xrj-h377-fr87 Rails Active Storage has possible Path Traversal in DiskService | Critical | Also affects activestorage |
| GHSA-r46p-8f7g-vvvg Rails Active Storage has a possible DoS vulnerability when in proxy mode via Range requests | High | Also affects activestorage |
| GHSA-qcfx-2mfw-w4cg Rails Active Storage has possible content type bypass via metadata in direct uploads | Medium | Also affects activestorage |
| GHSA-r4mg-4433-c7g3 Active Storage allowed transformation methods that were potentially unsafe | High | Also affects activestorage |
| GHSA-8h22-8cf7-hq6g Rails has possible Sensitive Session Information Leak in Active Storage | Medium | Also affects activestorage |
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