Date: Tue, 25 Feb 2020 08:12:26 +0100 From: Cedric Buissart <cbuissar@...hat.com> To: oss-security@...ts.openwall.com Subject: Re: Re: GNU screen "out of bounds access when setting w_xtermosc after OSC 49" On Mon, Feb 24, 2020 at 2:27 PM Cedric Buissart <cbuissar@...hat.com> wrote: > > Hi all, > > On Thu, Feb 6, 2020 at 5:55 PM Amadeusz Sławiński <amade@...blr.net> wrote: > > > > Hi, > > > > > > > > The fix commit is: > > > > > > --- > > > commit 68386dfb1fa33471372a8cd2e74686758a2f527b > > > Author: Amadeusz Slawinski <amade@...blr.net> > > > Date: Thu Jan 30 17:56:27 2020 +0100 > > > > > > Fix out of bounds access when setting w_xtermosc after OSC 49 > > > > > > echo -e "\e]49\e; \n\ec" > > > crashes screen. > > > > > > This happens because 49 is divided by 10 and used as table index > > > resulting in access to w_xtermosc, which is out of bounds with table > > > itself being size 4. Increase size of table by 1 to 5, which is enough > > > for all current uses. > > > > > > As this overwrites memory based on user input it is potential security > > > issue. > > > > > > Reported-by: pippin@...p.org > > > Signed-off-by: Amadeusz Slawinski <amade@...blr.net> > > > --- > > > > > > This is followed by another related commit: > > > > > > --- > > > commit 0dd53533e20d2948351a99ec5336fbc9b82b226a > > > Author: Amadeusz Slawinski <amade@...blr.net> > > > Date: Wed Feb 5 21:05:28 2020 +0100 > > > > > > Increase permitted length of OSC > > > > > > hyperlink feature used by some terminals requires lots of characters > > > https://gist.github.com/egmontkob/eb114294efbcd5adb1944c9f3cb5feda#length-limits > > > mentions around 2083 characters, set it to a bit more. > > > > > > Bug: 57718 > > > > > > Signed-off-by: Amadeusz Slawinski <amade@...blr.net> > > > --- > > > > > > Combined, these two commits change: > > > > > > char w_xtermosc[MAXSTR]; /* special xterm/rxvt escapes */ > > > > > > (where MAXSTR is 768) to: > > > > > > char w_xtermosc; /* special xterm/rxvt escapes */ > > > > > > > The report which resulted in second commit just happened to be reported > > at similar time and is not related to the issue at hand apart from same > > location in source code. > > > > > These are as seen on the screen-v4 branch. On that branch, and thus in > > > all screen releases so far, the bug appears to be exposed only when > > > building with the "--enable-rxvt_osc" option. Builds and packages made > > > without that option appear to be safe. Amadeusz, can you confirm this? > > > > Yes builds without this option should be safe, however do note that > > as far as I know most distributions do enable it (I checked Debian, > > Arch Linux, Fedora and Gentoo). > > > > > > > > On master branch, the functionality is always enabled (and the option is > > > dropped), thus (not too ancient) builds from that branch are vulnerable > > > (until the above fixes, which were also made to that branch). > > > > Yes, however do note that all v4 releases are done from screen-v4 branch. > Has a CVE been requested already ? > I do not see one on cve.mitre.org CVE-2020-9366 was assigned to this flaw via mitre.org > > > > Amadeusz > > > > > -- > Cedric Buissart, > Product Security -- Cedric Buissart, Product Security
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