Sudoedit can edit arbitrary files

Sudoedit can edit arbitrary files(seclists.org)

109 points by accessvector 3 years ago | 55 comments

throw0101c 3 years ago |

I find it handy that most distros have a CVE look-up 'service':

* https://security-tracker.debian.org/tracker/CVE-2023-22809

* https://ubuntu.com/security/CVE-2023-22809

* https://bugzilla.redhat.com/show_bug.cgi?id=CVE-2023-22809

Debian has links to the others.

mroche 3 years ago | |

I would opt for the Red Hat CVE Database over Bugzilla if you aren't using Fedora, but they all interlink:

https://access.redhat.com/security/cve/CVE-2023-22809

Red Hat has quite a few services under the /security path.

sva_ 3 years ago | |

https://security.archlinux.org/

_ikke_ 3 years ago | |

https://security.alpinelinux.org/vuln/CVE-2023-22809

tinus_hn 3 years ago |

Does this really work? The command is supposed to copy the original file to a temporary file, run the edit command with the privileges of the original user and then copy the edited file over the original. Otherwise what’s stopping an attacker from telling the editor to just open another file?

DSMan195276 3 years ago | |

Yeah I had the same confusion, the linked PDF explains it. Basically sudo determines the list of files to edit after expanding the `EDITOR` variable into separate arguments, and the `--` in the argument list (added by `sudo`) is used to determine where the file arguments provided to `sudoedit` start in the new argument list.

By adding your own `--` in the `EDITOR` variable, `sudo` gets confused and thinks that `--` is the start of the `sudoedit` file arguments and thus happily copies and edits all the files after it.

tinus_hn 3 years ago | | |

Incredible! So the problem is not -- but the problem is that it is checking the wrong thing to begin with. Why even parse the string, sudo already had the list of files when it constructed the string..

eklitzke 3 years ago | |

You're correct but sudoedit itself needs to parse the file list to know which files to copy to temporary files as you describe. So in this case you're tricking sudoedit into thinking you want to edit a different file than the one specified originally on the command line.

dejj 3 years ago |

Why is this a problem, given that one can easily use sudoedit for privilege escalation already?

edit: I now realize I have confused sudoedit with visudo

jboy55 3 years ago | |

I read it at first take as if it was "CVE-2023-32049: 'su' has critical privilege escalation venerability"

arp242 3 years ago | |

Read the link instead of replying based on the title.

orf 3 years ago |

The fix: https://github.com/sudo-project/sudo/commit/0274a4f3b403162a...

michalsustr 3 years ago |

Why would one prefer to add sudoedit X to sudoers rather than updating file access privileges of X directly?

Just curious about arguments for this use case.

throw0101c 3 years ago | |

> Why would one prefer to add sudoedit X to sudoers rather than updating file access privileges of X directly?

Permission complications.

Software may run as user:group, but you don't want to add humans to either, and so you allow them to edit a few files as that user or group from their own account (which also gives you auditing of changes). Some software insists on files (directories) have certain permissions so you're stuff with them.

Or you want a centralized place for permissions, so you put these sudoedit entries in LDAP which can be accessed anywhere in you network, and so you don't have to keep track of individual file permissions on a gazillion systems.

eklitzke 3 years ago | |

Sudo basically has an ACL-like system where you can specify exactly which users/groups can execute which commands as root. So you can say user foo can execute commands X, Y, and Z as root and user bar can execute commands W, Y, and Z as root, and neither user can use sudo to execute any other command as root. The ACL system isn't for sudoedit specifically, it's a general feature of sudo.

As to why you can't just update access privileges of the file, for most use cases you probably could do that. If you need something more complicated though you'll have to use some terrible ACL implementation like the one in sudo or Posix file ACLs.

mananaysiempre 3 years ago | | |

I recently got to reading the POSIX.1e (MAC & DAC) draft, and the DAC = ACL part is... surprisingly non-terrible. Still awkward and hampered by its existence as barely-visible metadata smeared over the whole system, as all ACLs are, but not at all the hopeless mess I expected coming from NT. (Even that might’ve been salvageable had Microsoft been willing to publish full documentation of all NT object permissions and mechanisms. Except SDDL, there is no world in which SDDL is salvageable.) Couldn’t make heads or tails of the MAC part, though.

The /etc/sudoers solution does have a usability advantage precisely in not being smeared all over the system. Even if “/etc/sudoers” and “usability” are words not often seen inside a single sentence.

dllthomas 3 years ago | |

In addition to what has been said already, sometimes it's nice to have guard rails, so you're a little more sure that you're only touching that thing when you mean to.

stabbles 3 years ago |

I wonder if this bug in logic (instead of buffer overflows) would also have been less likely in a different language. Would it have been more obvious in a language where it's easier to work with dynamically allocated arrays and strings?

inopinatus 3 years ago |

Consider this a prompt to review your /etc/sudoers for any utility whose behaviour is modified by environment variables in the env_keep list.

remram 3 years ago | |

I don't think that's what's happening. sudoedit does NOT run the editor as root, it copies the file to a temporary as root, runs the editor as you, and copies the temporary over the target file as root when you're done editing it (at least it's supposed to).

inopinatus 3 years ago | | |

Looks like a misclick, but unsure which comment was intended for this reply.

syrrim 3 years ago |

Is there a patch, or more detailed explanation of what causes this?

nequo 3 years ago | |

Ubuntu shipped the patch three days ago. The output of `apt changelog sudo` on 22.04 LTS:

  sudo (1.9.9-1ubuntu2.2) jammy-security; urgency=medium

    * SECURITY UPDATE: arbitrary file overwrite via sudoedit
      - debian/patches/CVE-2023-22809.patch: do not permit editor arguments
        to include -- in plugins/sudoers/editor.c, plugins/sudoers/sudoers.c,
        plugins/sudoers/visudo.c.
      - CVE-2023-22809
    * SECURITY UPDATE: DoS via invalid arithmetic shift in Protobuf-c
      - debian/patches/CVE-2022-33070.patch: only shift unsigned values in
        lib/protobuf-c/protobuf-c.c.
      - CVE-2022-33070

   -- Marc Deslauriers <marc.deslauriers@ubuntu.com>  Mon, 16 Jan 2023 07:36:33 -0500

There is a detailed explanation on the sudo website: https://www.sudo.ws/security/advisories/sudoedit_any/

slaymaker1907 3 years ago | |

There's a detailed writeup mentioned in the post https://www.synacktiv.com/sites/default/files/2023-01/sudo-C....

asveikau 3 years ago | |

It shells out to the EDITOR environment variable, which is controlled by the less privileged user.

In this example they inject running an editor against another file.

I'm guessing you can put arbitrary code in there or point it at a locally controlled executable too. But I'm not sure. Maybe sudoedit puts more scrutiny on that variable than most, non-security programs. At any rate many text editors have lots of modules and scripting and can presumably load and execute code as the privileged user.

The workaround is to change the sudo config file to remove the EDITOR environment variable and a few others.

zokier 3 years ago | | |

> At any rate many text editors have lots of modules and scripting and can presumably load and execute code as the privileged user.

Sudoedit does not run the editor as privileged user, that is kinda the whole point

binkHN 3 years ago |

I moved to https://man.openbsd.org/doas long ago.

shashasha2 3 years ago | |

Is doas safe about this exploit or does it have the same problem ?

yencabulator 3 years ago | | |

doas has no "doasedit". It's a lot simpler than sudo, on purpose.