CVE-2024-29186
MEDIUMSlow String Operations via MultiPart Requests in Event-Driven Functions
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Blast Radius
bref/brefReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Packagist packages — download data is not available via public APIs for these ecosystems.
Description
Bref is an open-source project that helps users go serverless on Amazon Web Services with PHP. When Bref prior to version 2.1.17 is used with the Event-Driven Function runtime and the handler is a RequestHandlerInterface, then the Lambda event is converted to a PSR7 object. During the conversion process, if the request is a MultiPart, each part is parsed. In the parsing process, the Content-Type header of each part is read using the Riverline/multipart-parser library.
The library, in the StreamedPart::parseHeaderContent function, performs slow multi-byte string operations on the header value.
Precisely, the mb_convert_encoding function is used with the first ($string) and third ($from_encoding) parameters read from the header value.
An attacker could send specifically crafted requests which would force the server into performing long operations with a consequent long billed duration.
The attack has the following requirements and limitations: The Lambda should use the Event-Driven Function runtime and the RequestHandlerInterface handler and should implement at least an endpoint accepting POST requests; the attacker can send requests up to 6MB long (this is enough to cause a billed duration between 400ms and 500ms with the default 1024MB RAM Lambda image of Bref); and if the Lambda uses a PHP runtime <= php-82, the impact is higher as the billed duration in the default 1024MB RAM Lambda image of Bref could be brought to more than 900ms for each request. Notice that the vulnerability applies only to headers read from the request body as the request header has a limitation which allows a total maximum size of ~10KB.
Version 2.1.17 contains a fix for this issue.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | bref/bref | all versions | 2.1.17 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for bref/bref. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update bref/bref to 2.1.17 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2024-29186 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2024-29186 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2024-29186. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2024-29186 in your dependencies?
O3 detects CVE-2024-29186 across Packagist dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.