A stack-based buffer overflow flaw was found in the X.Org X server and Xwayland. A mismatch between the X server and the libXfont2 library's maximum font name length can cause a stack buffer overflow during font alias resolution. The server allocates a 256 byte stack buffer but libXfont2's alias target name length is 1024 bytes. A font alias name between 257 and 1023 bytes causes the X server to copy that name into the undersized stack buffer without further checks. This may be used to crash the server, or for privilege escalation if the X server runs as root.
https://lists.x.org/archives/xorg-announce/2026-June/003702.html
https://access.redhat.com/errata/RHSA-2026:49519
https://access.redhat.com/errata/RHSA-2026:46473
https://access.redhat.com/errata/RHSA-2026:46460
https://access.redhat.com/errata/RHSA-2026:46456
https://access.redhat.com/errata/RHSA-2026:46392
https://access.redhat.com/errata/RHSA-2026:46385
https://access.redhat.com/errata/RHSA-2026:46382
https://access.redhat.com/errata/RHSA-2026:46377
https://access.redhat.com/errata/RHSA-2026:38810
https://access.redhat.com/errata/RHSA-2026:38502
https://access.redhat.com/errata/RHSA-2026:36798
https://access.redhat.com/errata/RHSA-2026:36792
https://access.redhat.com/errata/RHSA-2026:36791
https://access.redhat.com/errata/RHSA-2026:36768
https://access.redhat.com/errata/RHSA-2026:36634
https://access.redhat.com/errata/RHSA-2026:36633
https://access.redhat.com/errata/RHSA-2026:36632
https://access.redhat.com/errata/RHSA-2026:36087
https://access.redhat.com/errata/RHSA-2026:36086
https://access.redhat.com/errata/RHSA-2026:36085
https://access.redhat.com/errata/RHSA-2026:36083
https://access.redhat.com/errata/RHSA-2026:29844
https://access.redhat.com/errata/RHSA-2026:28923
https://access.redhat.com/errata/RHSA-2026:26709
https://access.redhat.com/errata/RHSA-2026:26610
https://access.redhat.com/errata/RHSA-2026:26590
https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-50256.json
https://redhat.atlassian.net/browse/PSIRTSUPT-16950
https://gitlab.freedesktop.org/xorg/xserver/-/commit/bb5158f962dc935e58ef8b4b5fcb31be201a6e07
https://euvd.enisa.europa.eu/vulnerability/EUVD-2026-34813