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Date: Wed, 27 Mar 2024 19:00:02 -0400
From: Demi Marie Obenour <demi@...isiblethingslab.com>
To: oss-security@...ts.openwall.com
Subject: Re: CVE-2024-28085: Escape sequence injection in
 util-linux wall

On Wed, Mar 27, 2024 at 10:30:41PM +0100, Jakub Wilk wrote:
> While looking through upstream git for a fix for this┬╣, I stumbled upon
> another write(1)/wall(1) control character injection vulnerability,
> introduced last year in util-linux v2.39.
> 
> The offending commits are:
> 
> * https://github.com/util-linux/util-linux/commit/8a7b8456d1dc0e7c
>   ("write: correctly handle wide characters")
> * https://github.com/util-linux/util-linux/commit/aa13246a1bf1be9e
>   ("wall: use fputs_careful()")
> 
> The added comment says:
> 
> > The locale of the recipient is nominally unknown,
> > but it's a solid bet that the encoding is compatible with the author's.
> 
> Alas the bet is not that solid when writer's locale encoding is controlled
> by an attacker.
> 
> We can exploit this against terminal emulators that recognize C1 control
> characters, such as Linux VTs or screen(1):
> 
>    $ printf '\302\23331mMOO\302\2330m\n' | LC_ALL=kk_KZ wall
> 
> I don't see any good way to fix this on the util-linux's side. It should be
> fixed on the terminal emulators' side by disabling C1 support.
> 
> 
> ┬╣ https://github.com/util-linux/util-linux/commit/404b0781f52f7c04
>   ("wall: fix escape sequence Injection [CVE-2024-28085]")

Would enforcing UTF-8 validity (regardless of user locale) be a
solution?
-- 
Sincerely,
Demi Marie Obenour (she/her/hers)
Invisible Things Lab

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