Avoid world-writable directory permissions

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Metadata

ID: rust-security/mkdir-world-writable-permissions

Language: Rust

Severity: Warning

Category: Security

CWE: 732

Related CWEs:

Description

Creating a directory with DirBuilder::new().mode(0o777) (or any other mode whose “other” triplet has the write bit set) lets any local user add, remove, or replace files inside the directory regardless of the individual files’ permissions. This can enable symlink attacks, race conditions during file replacement, and privilege escalation if a privileged process later reads or executes files from the directory. Prefer 0o755 for directories that need to be world-readable or 0o750 to restrict to a group.

Learn More

CWE-732: Incorrect Permission Assignment for Critical Resource

Non-Compliant Code Examples

use std::fs::DirBuilder;
use std::os::unix::fs::DirBuilderExt;

fn invalid() -> std::io::Result<()> {
    // World-writable — classic mistakes
    DirBuilder::new().mode(0o777).create("/tmp/a")?;
    DirBuilder::new().mode(0o666).create("/tmp/b")?;

    // Other world-writable triplets
    DirBuilder::new().mode(0o776).create("/tmp/c")?;    // last digit 6 — rw for others
    DirBuilder::new().mode(0o002).create("/tmp/d")?;    // last digit 2 — write only
    DirBuilder::new().mode(0o773).create("/tmp/e")?;    // last digit 3 — wx for others

    // 4-digit (with sticky/setuid) — still world-writable
    DirBuilder::new().mode(0o7777).create("/tmp/f")?;

    // Fully qualified path
    std::fs::DirBuilder::new().mode(0o777).create("/tmp/g")?;

    // Underscore separators
    DirBuilder::new().mode(0o7_7_7).create("/tmp/h")?;

    Ok(())
}

Compliant Code Examples

use std::fs::DirBuilder;
use std::os::unix::fs::DirBuilderExt;

fn valid() -> std::io::Result<()> {
    // Valid modes — no world write
    DirBuilder::new().mode(0o755).create("/tmp/a")?;     // world-readable, not writable
    DirBuilder::new().mode(0o750).create("/tmp/b")?;     // group-readable only
    DirBuilder::new().mode(0o700).create("/tmp/c")?;     // owner-only
    DirBuilder::new().mode(0o770).create("/tmp/d")?;     // group-writable but NOT world
    DirBuilder::new().mode(0o740).create("/tmp/e")?;     // last digit 0 — fine

    Ok(())
}