Summary
Package updates are available for Amazon Linux 2023 that fix the following vulnerabilities: CVE-2026-50264: An out-of-bounds write flaw was found in the X.Org X server and Xwayland in DRIGetBuffers/DRIGetBuffersWithFormat. A client that requests multiple DRI2BufferBackLeft attachments and one DRI2BufferFrontLeft can trigger an out-of-bounds heap write. This may be used to crash the server, or for privilege escalation if the X server runs as root. CVE-2026-50263: A use-after-free flaw was found in the X.Org X server and Xwayland in CreateSaverWindow(). A client can trigger a use-after-free read after changing window attributes and forcing the screen saver, leading to information disclosure. CVE-2026-50262: 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. CVE-2026-50261: A use-after-free flaw was found in the X.Org X server and Xwayland 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. This may be used to crash the server, or for privilege escalation if the X server runs as root. CVE-2026-50260: A use-after-free flaw was found in the X.Org X server and Xwayland 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. This may be used to crash the server, or for privilege escalation if the X server runs as root. CVE-2026-50259: A stack-based buffer overflow flaw was found in the X.Org X server and Xwayland. _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. This may be used to crash the server, or for privilege escalation if the X server runs as root. CVE-2026-50258: A stack-based buffer overflow flaw was found in the X.Org X server and Xwayland. The X server has multiple stack buffers 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 stack overflows. This is caused by an incomplete fix of CVE-2025-26597. This may be used to crash the server, or for privilege escalation if the X server runs as root. CVE-2026-50257: 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. CVE-2026-50256: 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.
Fixed packages 12
| Release | Package | Fixed in |
|---|---|---|
| Amazon Linux · 2023 | tigervnc | 0:1.14.1-3.amzn2023.0.6 |
| Amazon Linux · 2023 | tigervnc-debuginfo | 0:1.14.1-3.amzn2023.0.6 |
| Amazon Linux · 2023 | tigervnc-debugsource | 0:1.14.1-3.amzn2023.0.6 |
| Amazon Linux · 2023 | tigervnc-icons | 0:1.14.1-3.amzn2023.0.6 |
| Amazon Linux · 2023 | tigervnc-license | 0:1.14.1-3.amzn2023.0.6 |
| Amazon Linux · 2023 | tigervnc-selinux | 0:1.14.1-3.amzn2023.0.6 |
| Amazon Linux · 2023 | tigervnc-server | 0:1.14.1-3.amzn2023.0.6 |
| Amazon Linux · 2023 | tigervnc-server-debuginfo | 0:1.14.1-3.amzn2023.0.6 |
| Amazon Linux · 2023 | tigervnc-server-minimal | 0:1.14.1-3.amzn2023.0.6 |
| Amazon Linux · 2023 | tigervnc-server-minimal-debuginfo | 0:1.14.1-3.amzn2023.0.6 |
| Amazon Linux · 2023 | tigervnc-server-module | 0:1.14.1-3.amzn2023.0.6 |
| Amazon Linux · 2023 | tigervnc-server-module-debuginfo | 0:1.14.1-3.amzn2023.0.6 |
Vulnerabilities 9
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High 7.8
Xorg-x11-server: xorg-x11-server-xwayland: xorg-x11-server: stack buffer overflow in font alias resolution due to libxfont2 name length mismatch
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 by…
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High 7.8
Xorg-x11-server: xorg-x11-server-xwayland: xorg-x11-server: use-after-free in misyncdestroyfence()
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…
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High 7.8
Xorg-x11-server: xorg-x11-server-xwayland: xorg-x11-server: stack buffer overflow in xkb key types due to unchecked shift levels
A stack-based buffer overflow flaw was found in the X.Org X server and Xwayland. The X server has multiple stack buffers sized XkbMaxShiftLevel * XkbNumKbdGroups but CheckKeyTypes() does not verify or clamp non-canonical key types to XkbMaxShiftLevel. A clien…
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High 7.8
Xorg-x11-server: xorg-x11-server-xwayland: xorg-x11-server: stack buffer overflow in xkb setmap request via mapwidths indexing
A stack-based buffer overflow flaw was found in the X.Org X server and Xwayland. _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 o…
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High 7.8
Xorg-x11-server: xorg-x11-server-xwayland: xorg-x11-server: use-after-free in freecounter()
A use-after-free flaw was found in the X.Org X server and Xwayland 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. This may …
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High 7.8
Xorg-x11-server: xorg-x11-server-xwayland: xorg-x11-server: use-after-free in syncchangecounter()
A use-after-free flaw was found in the X.Org X server and Xwayland 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. Th…
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High 7.8
Xorg-x11-server: xorg-x11-server-xwayland: xorg-x11-server: out-of-bounds heap write in dri2 drigetbuffers/drigetbufferswithformat
An out-of-bounds write flaw was found in the X.Org X server and Xwayland in DRIGetBuffers/DRIGetBuffersWithFormat. A client that requests multiple DRI2BufferBackLeft attachments and one DRI2BufferFrontLeft can trigger an out-of-bounds heap write. This may be …
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Medium 5.5
Xorg-x11-server: xorg-x11-server-xwayland: xorg-x11-server: out-of-bounds read/write in glx changedrawableattributes
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 wri…
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Medium 5.5
Xorg-x11-server: xorg-x11-server-xwayland: xorg-x11-server: use-after-free information disclosure in createsaverwindow()
A use-after-free flaw was found in the X.Org X server and Xwayland in CreateSaverWindow(). A client can trigger a use-after-free read after changing window attributes and forcing the screen saver, leading to information disclosure.
References
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web
https://alas.aws.amazon.com/cve/html/CVE-2026-50256.html
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web
https://alas.aws.amazon.com/cve/html/CVE-2026-50257.html
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web
https://alas.aws.amazon.com/cve/html/CVE-2026-50258.html
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web
https://alas.aws.amazon.com/cve/html/CVE-2026-50259.html
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web
https://alas.aws.amazon.com/cve/html/CVE-2026-50260.html
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web
https://alas.aws.amazon.com/cve/html/CVE-2026-50261.html
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web
https://alas.aws.amazon.com/cve/html/CVE-2026-50262.html
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web
https://alas.aws.amazon.com/cve/html/CVE-2026-50263.html
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web
https://alas.aws.amazon.com/cve/html/CVE-2026-50264.html