An issue was discovered in libX11 through 1.6.5. Functions ListExt.c:XListExtensions and GetFPath.c:XGetFontPath interpret a variable as signed instead of unsigned, resulting in an out-of-bounds write (of up to 128 bytes), leading to DoS or remote code execution.
Created libX11 tracking bugs for this issue:
Affects: fedora-all [bug 1623243]
Functions ListExt.c:XListExtensions and GetFPath.c:XGetFontPath interpret the length field, which is a char, as a signed value, resulting in a read and a write before the intended buffer when they traverse the list of extensions/paths provided by the server.
Is the fix going to be ported to RHEL 7?
This issue has been addressed in the following products:
Red Hat Enterprise Linux 7
Via RHSA-2019:2079 https://access.redhat.com/errata/RHSA-2019:2079
This bug is now closed. Further updates for individual products will be reflected on the CVE page(s):
To exploit the vulnerability an attacker would need to have already compromised the X server used by your applications. Normally, the X client that runs libX11 and the X server runs on the same machine, thus if an attacker can trigger this flaw he has already compromised the X server, which runs as root, and he has already full control on the system. If the X client runs on another system than the X server (e.g. DISPLAY environment variable is used and it points to an X server on another system) then exploiting this vulnerability would only gain the privileges of the client, which should not be run with high privileges. For the above reasons, this flaw was rated as Moderate Impact.