Package Instance

form-data uses unsafe random function in form-data for choosing boundary
### Summary

form-data uses `Math.random()` to select a boundary value for multipart form-encoded data. This can lead to a security issue if an attacker:
1. can observe other values produced by Math.random in the target application, and
2. can control one field of a request made using form-data

Because the values of Math.random() are pseudo-random and predictable (see: https://blog.securityevaluators.com/hacking-the-javascript-lottery-80cc437e3b7f), an attacker who can observe a few sequential values can determine the state of the PRNG and predict future values, includes those used to generate form-data's boundary value. The allows the attacker to craft a value that contains a boundary value, allowing them to inject additional parameters into the request.

This is largely the same vulnerability as was [recently found in `undici`](https://hackerone.com/reports/2913312) by [`parrot409`](https://hackerone.com/parrot409?type=user) -- I'm not affiliated with that researcher but want to give credit where credit is due! My PoC is largely based on their work.

### Details

The culprit is this line here: https://github.com/form-data/form-data/blob/426ba9ac440f95d1998dac9a5cd8d738043b048f/lib/form_data.js#L347

An attacker who is able to predict the output of Math.random() can predict this boundary value, and craft a payload that contains the boundary value, followed by another, fully attacker-controlled field. This is roughly equivalent to any sort of improper escaping vulnerability, with the caveat that the attacker must find a way to observe other Math.random() values generated by the application to solve for the state of the PRNG. However, Math.random() is used in all sorts of places that might be visible to an attacker (including by form-data itself, if the attacker can arrange for the vulnerable application to make a request to an attacker-controlled server using form-data, such as a user-controlled webhook -- the attacker could observe the boundary values from those requests to observe the Math.random() outputs). A common example would be a `x-request-id` header added by the server. These sorts of headers are often used for distributed tracing, to correlate errors across the frontend and backend. `Math.random()` is a fine place to get these sorts of IDs (in fact, [opentelemetry uses Math.random for this purpose](https://github.com/open-telemetry/opentelemetry-js/blob/2053f0d3a44631ade77ea04f656056a2c8a2ae76/packages/opentelemetry-sdk-trace-base/src/platform/node/RandomIdGenerator.ts#L22))

### PoC

PoC here: https://github.com/benweissmann/CVE-2025-7783-poc

Instructions are in that repo. It's based on the PoC from https://hackerone.com/reports/2913312 but simplified somewhat; the vulnerable application has a more direct side-channel from which to observe Math.random() values (a separate endpoint that happens to include a randomly-generated request ID). 

### Impact

For an application to be vulnerable, it must:
- Use `form-data` to send data including user-controlled data to some other system. The attacker must be able to do something malicious by adding extra parameters (that were not intended to be user-controlled) to this request. Depending on the target system's handling of repeated parameters, the attacker might be able to overwrite values in addition to appending values (some multipart form handlers deal with repeats by overwriting values instead of representing them as an array)
- Reveal values of Math.random(). It's easiest if the attacker can observe multiple sequential values, but more complex math could recover the PRNG state to some degree of confidence with non-sequential values. 

If an application is vulnerable, this allows an attacker to make arbitrary requests to internal systems.

Helm vulnerable to Code Injection through malicious chart.yaml content
A Helm contributor discovered that a specially crafted `Chart.yaml` file along with a specially linked `Chart.lock` file can lead to local code execution when dependencies are updated.

### Impact

Fields in a `Chart.yaml` file, that are carried over to a `Chart.lock` file when dependencies are updated and this file is written, can be crafted in a way that can cause execution if that same content were in a file that is executed (e.g., a `bash.rc` file or shell script). If the `Chart.lock` file is symlinked to one of these files updating dependencies will write the lock file content to the symlinked file. This can lead to unwanted execution. Helm warns of the symlinked file but did not stop execution due to symlinking.

This affects when dependencies are updated. When using the `helm` command this happens when `helm dependency update` is run. `helm dependency build` can write a lock file when one does not exist but this vector requires one to already exist. This affects the Helm SDK when the downloader `Manager` performs an update.

### Patches

This issue has been resolved in Helm v3.18.4

### Workarounds

Ensure the `Chart.lock` file in a chart is not a symlink prior to updating dependencies.

### For more information

Helm's security policy is spelled out in detail in our [SECURITY](https://github.com/helm/community/blob/master/SECURITY.md) document.

### Credits

Disclosed by Jakub Ciolek at AlphaSense.