react-native-blob-util is the actively maintained successor to the abandoned rn-fetch-blob, and moving to it is itself a meaningful security decision. The library handles file access and network data transfer in React Native apps: downloading files, uploading multipart form data, reading and writing local storage, and streaming large payloads without blowing up memory. If you are still on rn fetch blob react native code, the most important security fact is that you are running unmaintained software, and this fork exists to fix that.
The lineage is worth stating plainly. react-native-blob-util is a fork of rn-fetch-blob, which was itself a fork of react-native-fetch-blob. Both earlier packages are no longer maintained. react-native-blob-util is fully API-compatible with them, so it functions as a drop-in replacement while continuing to receive updates.
Why Migrating Off rn-fetch-blob Is a Security Move
An unmaintained dependency does not fail loudly. It just stops receiving fixes while the rest of the ecosystem moves on. When rn-fetch-blob stopped getting updates, any newly discovered issue in it, or in its own dependencies, had no upstream path to a patch. You were frozen.
react-native-blob-util inherits the same API surface but stays current with React Native releases and can absorb fixes. Because the migration is largely a matter of swapping the import, there is rarely a good reason to stay on the abandoned package:
// Before
import RNFetchBlob from "rn-fetch-blob";
// After
import ReactNativeBlobUtil from "react-native-blob-util";
The method signatures line up, so most codebases migrate with a find-and-replace plus a test pass. Treat "we are on rn-fetch-blob" as a finding your dependency scanner should raise, not a stable state.
What the Library Actually Handles
The security-relevant capabilities cluster around three areas:
- Network transfers — fetching files over HTTP(S), uploading multipart bodies, and streaming responses to disk instead of into memory.
- Filesystem access — reading, writing, and deleting files in app storage, cache, and platform-specific directories.
- Data encoding — moving between base64, UTF-8, and binary representations of file content.
Each of these touches data that may be untrusted or sensitive, which is where the real work lives. The library gives you the plumbing; using it safely is on you.
Handling Downloaded Files Safely
A file you download is untrusted input until proven otherwise. Two mistakes recur in React Native apps.
The first is trusting a server-supplied filename. If you write a downloaded file to a path built from a name the server chose, a value like ../../something can escape the directory you intended. Sanitize filenames and construct paths yourself rather than concatenating remote strings:
const safeName = remoteName.replace(/[^a-zA-Z0-9._-]/g, "_");
const dest = `${dirs.DocumentDir}/${safeName}`;
The second is skipping TLS validation. Some teams disable certificate checks to get past a self-signed cert in development and forget to re-enable them. Always transfer over HTTPS with validation on in production, and never ship a build that trusts arbitrary certificates.
Storage, Permissions, and Sensitive Data
Where you write a file determines who else can read it. On Android, external storage is broadly accessible to other apps; internal app storage is not. Downloading a token, a cached document, or personal data to a world-readable location leaks it to anything else on the device.
Default to app-private directories for anything sensitive, and reach for shared or external storage only when the user genuinely needs the file outside your app. Request the narrowest storage permission that gets the job done, and clean up temporary files rather than leaving decrypted content lingering in a cache directory. Handle large transfers as streams to disk so you are not holding sensitive blobs in memory longer than necessary.
Keeping the Dependency Itself Honest
react-native-blob-util is native code bridged into JavaScript, so it also carries its own transitive dependencies and platform bindings. Being maintained is necessary but not sufficient; you still want visibility into what version you run and whether it, or anything under it, has a known advisory.
Pin the version in your lockfile, review the release notes when you upgrade, and run software composition analysis across your React Native project so a flagged version surfaces automatically. An SCA tool such as Safeguard can flag a known-vulnerable native dependency transitively, which matters in mobile projects where the tree runs deep. Our SCA product page covers how that detection works, and comparing scanner coverage on our Snyk comparison page can help if you are choosing a tool.
FAQ
Is react-native-blob-util safe to use?
It is the maintained, actively developed successor to rn-fetch-blob and react-native-fetch-blob, which makes it the safer choice by default. As with any native dependency, pin the version, keep it updated, and scan it. Safety also depends on how you handle the files it moves.
Should I migrate from rn-fetch-blob to react-native-blob-util?
Yes. rn-fetch-blob is no longer maintained, so it receives no fixes. react-native-blob-util is API-compatible, so migration is usually a matter of swapping the import and running your tests.
What are the main security risks when handling files with this library?
Path traversal from trusting server-supplied filenames, disabled TLS validation on transfers, and writing sensitive data to world-readable storage. Sanitize filenames, keep certificate validation on, and use app-private directories for sensitive content.
Does react-native-blob-util have its own dependencies to worry about?
Yes. It is a native module with its own transitive dependencies. Pin its version, read release notes on upgrade, and run SCA so any known advisory in the tree is surfaced automatically.