CVE-2026-50263

A flaw was found in the X.Org X server related to an out-of-bounds read affecting XKB modifier map handling. An attacker with access to the X11 server can exploit this by sending a malformed request, leading to reading beyond intended memory boundaries.

A flaw was found in the X.Org X server that allows for out-of-bounds memory read in XKB geometry processing. An attacker can exploit this vulnerability to read uninitialized memory or out-of-bounds memory, potentially leading to memory disclosure or server crashes.

In the X.Org X server before 2017-06-19, a user authenticated to an X Session could crash or execute code in the context of the X Server by exploiting a stack overflow in the endianness conversion of X Events.

An out-of-bounds write flaw was found in the X.Org X server and Xwayland in DRIGetBuffers/DRIGetBuffersWithFormat. A client requesting multiple DRI2BufferBackLeft attachments and one DRI2BufferFrontLeft can trigger an out-of-bounds heap write.

An out-of-bounds read flaw was found in the X.Org X server and Xwayland in __glXDisp_ChangeDrawableAttributes(). A wrong size validation check can read a client-controlled number of bytes, exceeding the request buffer, leading to information disclosure. A write path also exists but requires byte-swapped clients which is disabled by default.

A use-after-free vulnerability was found in the X.Org X server and Xwayland in the SyncChangeCounter() function. A client setting up multiple SyncCounters can trigger this flaw by destroying those counters via a second client connection while they are being changed.

A use-after-free vulnerability was found in the X.Org X server and Xwayland in the FreeCounter() function. A client that sets up multiple SyncCounters and awaits on those triggers can trigger the flaw when destroying those counters via a second client connection.

A stack-based buffer overflow vulnerability was found in the X.Org X server and Xwayland. The _XkbSetMapChecks() function declares a fixed-size stack buffer mapWidths[256] indexed by key type, and the helper CheckKeyTypes() writes to it at a client-controlled offset, causing overflow.

A stack-based buffer overflow vulnerability was found in the X.Org X server and Xwayland. The CheckKeyTypes() function does not verify or clamp non-canonical key types to XkbMaxShiftLevel, allowing a client to set excessive shift levels and trigger stack overflows. This is caused by an incomplete fix of CVE-2025-26597.

A use-after-free vulnerability was found in the X.Org X server and Xwayland in the miSyncDestroyFence() function. A client setting up multiple fence triggers can cause a use-after-free function pointer call. An attacker connects to the X server to set up a fence and await it, then a second X connection destroys the fence, leading to use-after-free.