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Message-ID: <aiIMPvapb9WSKlHM@quokka>
Date: Fri, 5 Jun 2026 09:38:19 +1000
From: Peter Hutterer <peter.hutterer@...-t.net>
To: oss-security@...ts.openwall.com
Subject: Re: FW: X.Org Security Advisory: multiple security issues X.Org X
server and Xwayland
Hi all,
CVEs have been issued now, please see inline below
On Tue, Jun 02, 2026 at 10:01:46AM +1000, Peter Hutterer wrote:
> =======================================================================
> X.Org Security Advisory: June 2, 2026
>
> Issues in X.Org X server prior to 21.1.23 and Xwayland prior to 24.1.12
> =======================================================================
>
> Multiple issues have been found in the X server and Xwayland implementations
> published by X.Org for which we are releasing security fixes for in
> xorg-server-21.1.23 and xwayland-24.1.12.
>
> Note that CVEs have been requested for these issues but did not get assigned in
> time for this disclosure.
>
> * Font Alias Stack-based Buffer Overflow
>
> 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.
>
> Fixed in: xorg-server-21.1.23 and xwayland-24.1.12
> Fix: https://gitlab.freedesktop.org/xorg/xserver/-/commit/bb5158f962dc935e58ef8b4b5fcb31be201a6e07
> Found by: Anonymous working with TrendAI Zero Day Initiative.
> (ZDI-CAN-30136)
This issue has been assigned CVE-2026-50256
> * XSYNC Use-After-Free 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.
>
> Fixed in: xorg-server-21.1.23 and xwayland-24.1.12
> Fix: https://gitlab.freedesktop.org/xorg/xserver/-/commit/f5abfb61994471023d8c6470428c8e30c411cc0b
> Found by: Anonymous working with TrendAI Zero Day Initiative.
> (ZDI-CAN-30159)
This issue has been assigned CVE-2026-50257
> * XKB Key Types Stack-based Buffer Overflow
>
> The X server has multiple stack buffers that are sized
> XkbMaxShiftLevel * XkbNumKbdGroups but CheckKeyTypes() does not verify
> or clamp non-canonical key types to XkbMaxShiftLevel. A client can
> change key types to excessive shift levels and trigger three separate
> stack overflows.
>
> This is caused by an incomplete fix of CVE-2025-26597.
>
> Fixed in: xorg-server-21.1.23 and xwayland-24.1.12
> Fix: https://gitlab.freedesktop.org/xorg/xserver/-/commit/543e108516428fc8c3bea91d6563ad266f9a801e
> Found by: Anonymous working with TrendAI Zero Day Initiative.
> (ZDI-CAN-30160)
This issue has been assigned CVE-2026-50258
> * XKB SetMap Request Stack-based Buffer Overflow
>
> _XkbSetMapChecks() declares a fixed-size stack buffer mapWidths[256]
> indexed by key type index. The helper function CheckKeyTypes() writes
> to this buffer at a client-controlled offset, allowing a stack buffer
> overflow.
>
> Fixed in: xorg-server-21.1.23 and xwayland-24.1.12
> Fix: https://gitlab.freedesktop.org/xorg/xserver/-/commit/867b59b33bee669cb412f1314e47c52eacf6e00b
> Found by: Anonymous working with TrendAI Zero Day Initiative.
> (ZDI-CAN-30161)
This issue has been assigned CVE-2026-50259
> * XSYNC Use-After-Free in FreeCounter()
>
> A client that sets up multiple SyncCounters and awaits on those
> triggers can trigger a use-after-free when destroying those counters
> via a second client connection.
>
> Fixed in: xorg-server-21.1.23 and xwayland-24.1.12
> Fix: https://gitlab.freedesktop.org/xorg/xserver/-/commit/f5abfb61994471023d8c6470428c8e30c411cc0b
> Found by: Anonymous working with TrendAI Zero Day Initiative.
> (ZDI-CAN-30163)
This issue has been assigned CVE-2026-50260
> * XSYNC Use-After-Free in SyncChangeCounter()
>
> A client that sets up multiple SyncCounters can trigger a use-after-free
> when destroying those counters via a second client connection while
> changing those counters.
>
> Fixed in: xorg-server-21.1.23 and xwayland-24.1.12
> Fix: https://gitlab.freedesktop.org/xorg/xserver/-/commit/bdd7bf57af208b1ddf57d4683d67104443b44812
> Found by: Anonymous working with TrendAI Zero Day Initiative.
> (ZDI-CAN-30164)
This issue has been assigned CVE-2026-50261
>
> * GLX ChangeDrawableAttributes Out-Of-Bounds Read/Write
>
> A wrong size validation check in __glXDisp_ChangeDrawableAttributes()
> can read (or write) a client-controlled number of bytes, exceeding
> the request buffer.
>
> The write path requires byte-swapped clients which is disabled by
> default.
>
> The read can lead to information disclosure, the write can be used
> to crash the server, or for privilege escalation if the X server runs
> as root.
>
> Fixed in: xorg-server-21.1.23 and xwayland-24.1.12
> Fix: https://gitlab.freedesktop.org/xorg/xserver/-/commit/6d459e4daf715bea8abdafa8fb130be2f8a1d145
> Found by: Anonymous working with TrendAI Zero Day Initiative.
> (ZDI-CAN-30165)
This issue has been assigned CVE-2026-50262
> * CreateSaverWindow Use-After-Free Information Disclosure
>
> A client can trigger a use-after-free read after changing window
> attributes and forcing the screen saver. This can lead to information
> disclosure.
>
> Fixed in: xorg-server-21.1.23 and xwayland-24.1.12
> Fix: https://gitlab.freedesktop.org/xorg/xserver/-/commit/ecc634f1b2f7aa473d3a267eada98c4918bf9e05
> Found by: Anonymous working with TrendAI Zero Day Initiative.
> (ZDI-CAN-30168)
This issue has been assigned CVE-2026-50263
> * DRI2 DRIGetBuffers/DRIGetBuffersWithFormat Out-Of-Bounds Write
>
> A client that requests multiple DRI2BufferBackLeft attachments and one
> DRI2BufferFrontLeft can trigger an out-of-bounds heap write.
>
> Fixed in: xorg-server-21.1.23 and xwayland-24.1.12
> Fix: https://gitlab.freedesktop.org/xorg/xserver/-/commit/339c279514326134b0878fc23ce6e9520440ce7f
> https://gitlab.freedesktop.org/xorg/xserver/-/commit/b7aa65cc3bb11b792ce2a3f511ba9b863acb11c8
> Found by: Peter Hutterer, Red Hat.
This issue has been assigned CVE-2026-50264
Cheers,
Peter
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