Debian Security Advisory

DLA-2666-1 libx11 -- LTS security update

Date Reported:
24 May 2021
Affected Packages:
Security database references:
In the Debian bugtracking system: Bug 988737.
In Mitre's CVE dictionary: CVE-2021-31535.
More information:

Roman Fiedler found that libX11, the X11 protocol client library, was vulnerable to protocol command injection due to insufficient validation of arguments to some functions.

For Debian 9 stretch, this problem has been fixed in version 2:1.6.4-3+deb9u4.

We recommend that you upgrade your libx11 packages.

For the detailed security status of libx11 please refer to its security tracker page at:

Further information about Debian LTS security advisories, how to apply these updates to your system and frequently asked questions can be found at: