High · published June 5, 2026
A use-after-free flaw was found in the X.Org X server and Xwayland in miSyncDestroyFence(). A client that sets up multiple fence triggers can trigger a use-after-free function pointer call. An attacker would connect to the X server to set up a fence and await that fence, then a second X connection destroys the fence, causing the use-after-free. This may be used to crash the server, or for privilege escalation if the X server runs as root.
| Product | Versions | Fixed in |
|---|---|---|
| x.org/x_server | < 21.1.23 | 21.1.23 |
| x.org/xwayland | < 24.1.12 | 24.1.12 |
| redhat/enterprise_linux | all versions | — |
| redhat/enterprise_linux | all versions | — |
| redhat/enterprise_linux | all versions | — |
| redhat/enterprise_linux | all versions | — |