MAL-2026-4503

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Import Source
https://github.com/ossf/malicious-packages/blob/main/osv/malicious/npm/bytecore/MAL-2026-4503.json
JSON Data
https://api.osv.dev/v1/vulns/MAL-2026-4503
Published
2026-05-19T16:57:09Z
Modified
2026-05-26T06:02:16.441614374Z
Summary
Malicious code in bytecore (npm)
Details

-= Per source details. Do not edit below this line.=-

Source: amazon-inspector (1c1ddd2dea35052822d2dc89f0f46ceae20c772c257e0c97f0024483e9ff31c0)

The package masquerades as a pino-like logging middleware (README is copied from pino, exports a pino property, mimics pino's option shape) but the middleware factory in index.js spawns a detached node lib/caller.js child process when the exported function is invoked. lib/caller.js obfuscates a hardcoded C2 URL by shadowing the real process global with a local object whose env holds base64-encoded strings; decoding DEV_API_KEY yields https://jsonkeeper.com/b/BADC6. The script GETs that anonymous, mutable paste host with axios (retried 5 times) and passes the response body to new Function.constructor("require", s)(require), executing attacker-controlled JavaScript with full Node privileges and direct access to require. Any application that installs bytecore and mounts the middleware (app.use(require('bytecore')())) runs whatever code the paste currently serves. The combination of (a) mutable anonymous paste host as code source, (b) require-passing eval of fetched bytes, (c) base64 + process-shadowing obfuscation of the C2, and (d) impersonation of a popular logger to lure installers is an unambiguous remote-code-execution backdoor.

Database specific 
{
    "malicious-packages-origins": [
        {
            "id": "IN-MAL-2026-003203",
            "versions": [
                "5.3.1"
            ],
            "sha256": "1c1ddd2dea35052822d2dc89f0f46ceae20c772c257e0c97f0024483e9ff31c0",
            "source": "amazon-inspector",
            "modified_time": "2026-05-19T16:57:09Z",
            "import_time": "2026-05-26T05:50:12.370992922Z"
        }
    ]
}
References
Credits

Affected packages

npm / bytecore

Package

Name
bytecore
View open source insights on deps.dev
Purl
pkg:npm/bytecore

Affected ranges

Affected versions

5.*
5.3.1

Database specific

cwes 
[
    {
        "description": "The product contains code that appears to be malicious in nature.",
        "name": "Embedded Malicious Code",
        "cweId": "CWE-506"
    }
]
indicators 
{
    "evidence_files": [
        {
            "path": "lib/caller.js",
            "sha256": "5f2d8aec684e79cb983af79d29fddf7e7ecf1e36474baf1422e77c9b79caee23",
            "tlsh": "d6019c4a70fd641c016122fa261fa4326011f47b3946d9d4374cc3525fa96be2e93adf"
        },
        {
            "path": "README.md",
            "sha256": "366fb8e84a0157e29ec26bad87f74f0564804a80eb71b0fa22cc1eb08a88cbf4",
            "tlsh": "4a5175a787e87b6e4b6300b1a1c275b9ff1f931c7b69606dec9cd1291319997813110a"
        }
    ],
    "package_integrity": [
        {
            "filename": "bytecore-5.3.1.tgz",
            "hashes": {
                "sha512_sri": "sha512-Fz+0+98cioSWu+Opl6Kfd7YZ/Bm640khK7qi5szklKrGs6nspU+A7TA7HpesE5/Nd5CK2ibXvmvsnQs8aJV7Yg==",
                "sha1": "ea2bf63152f2c687850dfb8a66d404424193b068"
            }
        }
    ]
}
source 
"https://github.com/ossf/malicious-packages/blob/main/osv/malicious/npm/bytecore/MAL-2026-4503.json"