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CVE-2026-56000 is a heap use-after-free vulnerability in the GLX extension of X.Org Server and Xwayland. The flaw is in CommonMakeCurrent(), which stores oldTag as a pointer into the per-client contextTags array. During processing of a crafted sequence of GLX MakeCurrent operations, CommonMakeNewCurrent() can trigger allocation growth for that array, causing realloc() to move the underlying buffer and leaving oldTag as a dangling pointer. The subsequent GlxFreeContextTag(oldTag) operation then writes to freed heap memory. The issue affects xorg-server versions before 21.1.24 and Xwayland versions before 24.1.13. The bug can be triggered by a client able to connect to the X server and issue GLX requests, including a sequence that exhausts the initial context tag slots and forces reallocation.
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A heap use-after-free vulnerability in X.Org xorg-server and xwayland involving CommonMakeCurrent(), allowing a local attacker with an X connection and ability to provide a GLX context to trigger memory corruption.
A use-after-free vulnerability in the X.Org X server GLX CommonMakeCurrent logic, where realloc of the contextTags array can invalidate oldTag and subsequent GlxFreeContextTag(oldTag) writes into freed memory.
Use-after-free vulnerability in X.Org Server/Xwayland GLX contextTags handling within CommonMakeCurrent(), caused by stale pointer use after realloc(), potentially leading to memory corruption.
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