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high severity

Remote Code Execution (RCE)

  • Vulnerable module: pac-resolver
  • Introduced through: pac-resolver@3.0.0

Detailed paths

  • Introduced through: pac-resolver@3.0.0
    Remediation: Upgrade to pac-resolver@5.0.0.


Affected versions of this package are vulnerable to Remote Code Execution (RCE). This can occur when used with untrusted input, due to unsafe PAC file handling.

NOTE: The fix for this vulnerability is applied in the node-degenerator library, a dependency written by the same maintainer.


const pac = require('pac-resolver');

// Should keep running forever (if not vulnerable):
setInterval(() => {
    console.log("Still running");
}, 1000);

// Parsing a malicious PAC file unexpectedly executes unsandboxed code:
    // Real PAC config:
    function FindProxyForURL(url, host) {
        return "DIRECT";

    // But also run arbitrary code:
    var f = this.constructor.constructor(\`
        // Running outside the sandbox:
        console.log('Read env vars:', process.env);
        console.log('!!! PAC file is running arbitrary code !!!');
        console.log('Can read & could exfiltrate env vars ^');
        console.log('Can kill parsing process, like so:');
        process.exit(100); // Kill the vulnerable process
        // etc etc



Upgrade pac-resolver to version 5.0.0 or higher.


high severity

Server-side Request Forgery (SSRF)

  • Vulnerable module: netmask
  • Introduced through: netmask@1.0.6

Detailed paths

  • Introduced through: pac-resolver@3.0.0 netmask@1.0.6
    Remediation: Upgrade to pac-resolver@4.1.1.


netmask is a library to parse IPv4 CIDR blocks.

Affected versions of this package are vulnerable to Server-side Request Forgery (SSRF). It incorrectly evaluates individual IPv4 octets that contain octal strings as left-stripped integers, leading to an inordinate attack surface on hundreds of thousands of projects that rely on netmask to filter or evaluate IPv4 block ranges, both inbound and outbound.

For example, a remote unauthenticated attacker can request local resources using input data 0177.0.0.1 (, which netmask evaluates as the public IP Contrastingly, a remote authenticated or unauthenticated attacker can input the data 0127.0.0.01 ( as localhost, yet the input data is a public IP and can potentially cause local and remote file inclusion (LFI/RFI). A remote authenticated or unauthenticated attacker can bypass packages that rely on netmask to filter IP address blocks to reach intranets, VPNs, containers, adjacent VPC instances, or LAN hosts, using input data such as (, which netmask evaluates as (public).


Upgrade netmask to version 2.0.1 or higher.