Bug#354709: screen corrupts my display when viewing certain spam mails (via mutt)

[Thadeu Lima de Souza Cascardo]

On Tue, Sep 26, 2017 at 12:39:19AM +0200, Axel Beckert wrote:
> Control: tag -1 - moreinfo + confirmed
> Control: found -1 4.1.0~20120320gitdb59704-7+deb7u1
> 
> Hi Cascardo,
> 
> Thadeu Lima de Souza Cascardo wrote:
> > I have this same problem with what seems to be valid UTF-8. One possible
> > reproduction test is running this on bash under screen.
> > 
> > echo -e '\xf0\x9f\x8d\x8c'
> > 
> > You will notice the extra space after that, which does not happen when
> > not under screen.
> 
> Thanks for the feedback and giving me a way to reproduce and test that
> (or at least a similar) issue. (And for the reminder that this bug
> report is still open. :-)
> 
> Unfortunately I can't reproduce it with your example.
> 
> I tried it with bash as well as with zsh inside a screen 4.6.1
> session, but everything looks fine.
> 

Sorry about that. My test was run with 4.5.0-6. It looks like 4.6.1 has
an updated Unicode support and that might have fixed it. As I run mutt
from screen from ssh from mosh, I realized mosh was to blame. When I
replaced it with ssh and used my system with screen 4.6.1-1, the problem
on mutt seemed to go away. So I would mark this as affecting 4.5.0-6,
but fixed at least in 4.6.1-1.

> I also tried
> 
> echo -e '\xf0\x9f\x8d\x8c'x
> 

I am using gnome-terminal, and if I don't use mosh, I see the banana. I
tested with both screen 4.5.0-6 and 4.6.1-1, and whenever using the
extra character, things seem to be printed fine (banana plus x, next
line rightly starting on the first column). If I only print the banana,
then 4.6.1-1 works fine, but 4.5.0-6 will have the prompt starting on
the second column. Tests were run with screen -U.

Interestingly, on some other versions of screen, without -U, I don't
see the banana, and adding extra characters will print them on the
previous line, overriding the previous prompt, which explains some of
the problems I see on mutt (an email with UTF-8 subject overriding the
previous email subject).

Thank you very much for maintaining screen. I will try to work with a
mosh bug now.

Cascardo.

> to see if there's a blank or similar directly behind that wide
> character (which shows up as a question mark inside a filled circle).
> 
> On which terminal did you happen to run into that? I have uxterm here.
> I also checked if any of my .screenrc settings could interfere, but
> nothing changed when commenting out any charset or terminal emulation
> related settings.
> 
> So I checked also gnome-terminal, but no luck there either.
> gnome-terminal showed me a banana btw., so this indeed seems to be
> valid UTF-8.
> 
> Then again, I ran into the original issue (spam displayed in mutt
> inside screen) at least with the screen version in Wheezy, so that one
> is definitely affected. (Your issue might or might not be the same
> issue. I'm not yet sure.) 
> 
> Next time I see such a case on Wheezy, I'll save a copy and check, if
> it's still present on Unstable.
> 
>   Regards, Axel
> -- 
>  ,''`.  |  Axel Beckert , https://people.debian.org/~abe/
> : :' :  |  Debian Developer, ftp.ch.debian.org Admin
> `. `'   |  4096R: 2517 B724 C5F6 CA99 5329  6E61 2FF9 CD59 6126 16B5
>   `-|  1024D: F067 EA27 26B9 C3FC 1486  202E C09E 1D89 9593 0EDE

Bug#354709: screen corrupts my display when viewing certain spam mails (via mutt)

[Axel Beckert]

Control: tag -1 - moreinfo + confirmed
Control: found -1 4.1.0~20120320gitdb59704-7+deb7u1

Hi Cascardo,

Thadeu Lima de Souza Cascardo wrote:
> I have this same problem with what seems to be valid UTF-8. One possible
> reproduction test is running this on bash under screen.
> 
> echo -e '\xf0\x9f\x8d\x8c'
> 
> You will notice the extra space after that, which does not happen when
> not under screen.

Thanks for the feedback and giving me a way to reproduce and test that
(or at least a similar) issue. (And for the reminder that this bug
report is still open. :-)

Unfortunately I can't reproduce it with your example.

I tried it with bash as well as with zsh inside a screen 4.6.1
session, but everything looks fine.

I also tried

echo -e '\xf0\x9f\x8d\x8c'x

to see if there's a blank or similar directly behind that wide
character (which shows up as a question mark inside a filled circle).

On which terminal did you happen to run into that? I have uxterm here.
I also checked if any of my .screenrc settings could interfere, but
nothing changed when commenting out any charset or terminal emulation
related settings.

So I checked also gnome-terminal, but no luck there either.
gnome-terminal showed me a banana btw., so this indeed seems to be
valid UTF-8.

Then again, I ran into the original issue (spam displayed in mutt
inside screen) at least with the screen version in Wheezy, so that one
is definitely affected. (Your issue might or might not be the same
issue. I'm not yet sure.) 

Next time I see such a case on Wheezy, I'll save a copy and check, if
it's still present on Unstable.

Regards, Axel
-- 
 ,''`.  |  Axel Beckert , https://people.debian.org/~abe/
: :' :  |  Debian Developer, ftp.ch.debian.org Admin
`. `'   |  4096R: 2517 B724 C5F6 CA99 5329  6E61 2FF9 CD59 6126 16B5
  `-|  1024D: F067 EA27 26B9 C3FC 1486  202E C09E 1D89 9593 0EDE

Bug#354709: screen corrupts my display when viewing certain spam mails (via mutt)

[Thadeu Lima de Souza Cascardo]

Package: screen
Version: 4.6.1-1
Followup-For: Bug #354709

Hi, Axel.

Thank you very much for your work maintaining screen.

I have this same problem with what seems to be valid UTF-8. One possible
reproduction test is running this on bash under screen.

echo -e '\xf0\x9f\x8d\x8c'

You will notice the extra space after that, which does not happen when
not under screen.

Thank you very much.
Cascardo.


-- System Information:
Debian Release: buster/sid
  APT prefers unstable-debug
  APT policy: (500, 'unstable-debug'), (500, 'unstable')
Architecture: amd64 (x86_64)
Foreign Architectures: i386, armhf

Kernel: Linux 4.11.0-2-amd64 (SMP w/4 CPU cores)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8), 
LANGUAGE=en_US.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)

Versions of packages screen depends on:
ii  libc6 2.24-17
ii  libpam0g  1.1.8-3.6
ii  libtinfo5 6.0+20170902-1
ii  libutempter0  1.1.6-3

screen recommends no packages.

Versions of packages screen suggests:
pn  byobu | screenie | iselect  
ii  ncurses-term6.0+20170902-1

-- no debconf information

Bug#354709: screen corrupts my display when viewing certain spam mails (via mutt)

[Axel Beckert]

Control: tag -1 + moreinfo

Hi Jon,

Jon Dowland wrote:
> On Sun, Sep 23, 2007 at 06:01:27PM +0200, Jan Christoph Nordholz wrote:
> > the UTF is invalid. "Regular" shells and ones inside screen behave
> > differently, presumably caused by that extra layer of indirection
> snip
> > I will try to find the exact cause, but I'm lowering the severity
> > since this only happens with invalid sequences.
> 
> Thanks. I'm vaguely worried that this could be exploited in some
> fashion. At present, the corruption is sufficient to have one row in
> mutt "overwrite" another, so you can delete the wrong mail etc., and
> that's by accident. I'm wondering what could be achieved on purpose...

I could no more reproduce this issue on Debian Sid, neither inside
uxterm nor inside urxvt nor inside gnome-terminal.

Can you check if you still have this issue?

Regards, Axel
-- 
 ,''`.  |  Axel Beckert , http://people.debian.org/~abe/
: :' :  |  Debian Developer, ftp.ch.debian.org Admin
`. `'   |  4096R: 2517 B724 C5F6 CA99 5329  6E61 2FF9 CD59 6126 16B5
  `-|  1024D: F067 EA27 26B9 C3FC 1486  202E C09E 1D89 9593 0EDE

Bug#354709: screen corrupts my display when viewing certain spam mails (via mutt)

[Jon Dowland]

On Sun, Sep 23, 2007 at 06:01:27PM +0200, Jan Christoph Nordholz wrote:
 the UTF is invalid. Regular shells and ones inside screen behave
 differently, presumably caused by that extra layer of indirection
snip
 I will try to find the exact cause, but I'm lowering the severity
 since this only happens with invalid sequences.

Thanks. I'm vaguely worried that this could be exploited in some
fashion. At present, the corruption is sufficient to have one row in
mutt overwrite another, so you can delete the wrong mail etc., and
that's by accident. I'm wondering what could be achieved on purpose...


-- 
Jon Dowland



-- 
To UNSUBSCRIBE, email to [EMAIL PROTECTED]
with a subject of unsubscribe. Trouble? Contact [EMAIL PROTECTED]

Bug#354709: screen corrupts my display when viewing certain spam mails (via mutt)

[Jan Christoph Nordholz]

severity 354709 minor
thankyou

Hi Jon,

the UTF is invalid. Regular shells and ones inside screen behave
differently, presumably caused by that extra layer of indirection:
e.g. echo -e '\xe6\xac__' displays one underline without, and two
within screen. (E6 starts a 3-byte UTF8 sequence. Regular shells
discard the whole invalid sequence - screen assumes that the sequence
was incomplete and discards only its (valid) head. This in turn seems
to confuse the inner (= mutt's) ncurses library, which expects the
standard behaviour.)

I will try to find the exact cause, but I'm lowering the severity
since this only happens with invalid sequences.


Regards,

Jan



-- 
To UNSUBSCRIBE, email to [EMAIL PROTECTED]
with a subject of unsubscribe. Trouble? Contact [EMAIL PROTECTED]

Bug#354709: screen corrupts my display when viewing certain spam mails (via mutt)

[Jon Dowland]

Package: screen
Version: 4.0.2-4.1
Severity: normal

Please find attached a tarball containing a Maildir with a
small selection of spam (`mutt-bug'), plus the problematic
spam isolated (`mutt-bug-one'). The filenames are because I
originally thought this was a mutt bug.

If I read the Maildir with mutt inside a screen session, the
display becomes very corrupted. If I read the same Maildir
with mutt outside of a screen session, the display is OK.

If you cat / otherwise inspect the individual file from
outside of screen, you should notice that it displays
differently than if you do so within a screen session
(although my display doesn't get destroyed).

In all cases my locale is set to en_GB.UTF-8. the `-U' flag
to screen does not change the results.

I am not a locale expert, I don't even know if the spam is
well-formed UTF, so I cannot offer much in the way of clues.
Perhaps mutt truncates the UTF subject line and the result
is un-closed multibyte UTF which screen is confused by...


-- System Information:
Debian Release: 3.1
  APT prefers unstable
  APT policy: (500, 'unstable')
Architecture: i386 (i686)
Kernel: Linux 2.6.11-jmtd
Locale: LANG=en_GB.UTF-8, LC_CTYPE=en_GB.UTF-8 (charmap=UTF-8)

Versions of packages screen depends on:
ii  base-passwd 3.5.9Debian base system master password
ii  debconf 1.4.30.13Debian configuration management sy
ii  libc6   2.3.2.ds1-22 GNU C Library: Shared libraries an
ii  libncursesw55.4-4Shared libraries for terminal hand
ii  libpam0g0.76-22  Pluggable Authentication Modules l
ii  passwd  1:4.0.3-31sarge5 change and administer password and

-- debconf information:
  screen/old_upgrade_prompt: false


screen-utf-issues.tar.gz
Description: Binary data