GHSA-74m5-2c7w-9w3x CVE-2023-30798 PYSEC-2023-48
MultipartParser denial of service with too many fields or files
- Severity
- 0.0 / 10
- High · CVSS 4.0
- Exploit chance (EPSS)
- 1.30%
- Chance of exploitation in the next 30 days. Higher than 70.42% of scored vulnerabilities.
- Known exploited
- No
- Not in CISA's catalog
- Weakness
- CWE-400 Uncontrolled Resource Consumption
- Fix
0.25.0- Upgrade starlette to this version or later
Description
Impact
The MultipartParser using the package python-multipart accepts an unlimited number of multipart parts (form fields or files).
Processing too many parts results in high CPU usage and high memory usage, eventually leading to an <abbr title="out of memory">OOM</abbr> process kill.
This can be triggered by sending too many small form fields with no content, or too many empty files.
For this to take effect application code has to:
- Have
python-multipartinstalled and - call
request.form()- or via another framework like FastAPI, using form field parameters or
UploadFileparameters, which in turn callsrequest.form().
- or via another framework like FastAPI, using form field parameters or
Patches
The vulnerability is solved in Starlette 0.25.0 by making the maximum fields and files customizable and with a sensible default (1000).
Applications will be secure by just upgrading their Starlette version to 0.25.0 (or FastAPI to 0.92.0).
If application code needs to customize the new max field and file number, there are new request.form() parameters (with the default values):
max_files=1000max_fields=1000
Workarounds
Applications that don't install python-multipart or that don't use form fields are safe.
In older versions, it's also possible to instead of calling request.form() call request.stream() and parse the form data in internal code.
In most cases, the best solution is to upgrade the Starlette version.
References
This was reported in private by @das7pad via internal email. He also coordinated the fix across multiple frameworks and parsers.
The details about how multipart/form-data is structured and parsed are in the RFC 7578.
Affected versions
PyPI
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.
starlette PyPI → 0.25.0
- pip
pip install --upgrade "starlette>=0.25.0"- poetry
poetry add "starlette>=0.25.0"- uv
uv add "starlette>=0.25.0"
Severity breakdown
CVSS 4.0 0.0
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
- Attack vector
- Network
- Attack complexity
- Low
- Attack requirements
- None
- Privileges required
- None
- User interaction
- None
- Confidentiality (vulnerable system)
- None
- Integrity (vulnerable system)
- None
- Availability (vulnerable system)
- High
- Confidentiality (subsequent systems)
- None
- Integrity (subsequent systems)
- None
- Availability (subsequent systems)
- None
CVSS 3.1 7.5
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- None
- Availability
- High
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.
References
Advisories
Packages
Other links
Timeline
- Published
- Last updated by the source
- Latest EPSS score
Related advisories
| Advisory | Severity | Why it's related |
|---|---|---|
| GHSA-86qp-5c8j-p5mr Starlette has missing Host header validation that poisons request.url.path, bypassing path-based security checks | Medium Known exploited | Also affects starlette |
| GHSA-82w8-qh3p-5jfq Starlette: request.form() limits silently ignored for application/x-www-form-urlencoded enable DoS | High | Also affects starlette |
| GHSA-jp82-jpqv-5vv3 Starlette: Unvalidated request path concatenated into authority poisons request.url.hostname | Medium | Also affects starlette |
| GHSA-wqp7-x3pw-xc5r Starlette: SSRF and NTLM credential theft via UNC paths in StaticFiles on Windows | High | Also affects starlette |
| GHSA-x746-7m8f-x49c Starlette: Arbitrary HTTP method dispatched to `HTTPEndpoint` attributes via `getattr` | Medium | Also affects starlette |
| GHSA-7f5h-v6xp-fcq8 Starlette vulnerable to O(n^2) DoS via Range header merging in ``starlette.responses.FileResponse`` | High | Also affects starlette |
| GHSA-2c2j-9gv5-cj73 Starlette has possible denial-of-service vector when parsing large files in multipart forms | Medium | Also affects starlette |
| GHSA-f96h-pmfr-66vw Starlette Denial of service (DoS) via multipart/form-data | High | Also affects starlette |
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