CVE-2026-109092 in xwayland
Summary
by MITRE • 11/13/2026
Incorrectly handled negative sizes when processing ProcXvShmPutImage requests in the X.Org xwayland before 24.1.15 and X Server before 21.1.26 could be used by local authenticated X clients to crash the X server or execute code.
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Analysis
by VulDB Data Team • 11/13/2026
The vulnerability identified involves a critical flaw in the handling of negative size parameters within ProcXvShmPutImage requests, affecting legacy versions of the X.Org xwayland component prior to version 24.1.15 and the X Server prior to version 21.1.26. This issue stems from insufficient validation of input data provided by local authenticated clients interacting with the X Window System via the Wayland compatibility layer. The ProcXvShmPutImage function is responsible for managing shared memory operations related to video overlay images, a feature historically used in multimedia applications to offload rendering tasks. When an attacker provides a negative value for image dimensions or buffer sizes during this process, the underlying C code fails to properly check these bounds before proceeding with memory allocation and copy operations. This lack of validation allows the system to interpret signed integers as unsigned values or proceed with invalid arithmetic, leading to severe memory corruption issues such as heap overflows or out-of-bounds writes.
From a technical perspective, this flaw represents a classic integer overflow or underflow vulnerability where negative inputs are not sanitized before being used in size calculations for memory buffers. In the context of the X Server architecture, which operates with high privileges and manages critical display resources, such an error can destabilize the entire graphical environment. The immediate operational impact is typically a denial of service, manifested as a crash or segmentation fault within the X server process. However, given that modern exploit techniques often leverage memory corruption primitives to achieve arbitrary code execution, this vulnerability poses a significant risk beyond simple disruption. An attacker who has gained local authentication access can craft specific malformed requests to trigger these invalid memory operations, potentially gaining control over the executing context of the X server.
This vulnerability aligns with Common Weakness Enumeration (CWE) categories such as CWE-190 Integer Overflow or Wraparound and CWE-20 Improper Input Validation. The attack vector is classified under local privilege escalation scenarios where an authenticated user exploits a flaw in system software to compromise integrity or availability. In terms of the MITRE ATT&CK framework, this activity corresponds to techniques involving exploitation for defense evasion or initial access if combined with other vectors, specifically falling under categories related to client-side attacks and resource manipulation. The ability to crash the server disrupts productivity and can be used as a precursor to more sophisticated attacks targeting sensitive data displayed on the screen or intercepting input events through compromised display servers.
Mitigation strategies primarily involve upgrading the X.Org xwayland component to version 24.1.15 or later, and ensuring that the underlying X Server is updated to version 21.1.26 or newer. These updates include patches that enforce strict validation of size parameters, rejecting negative values before they can influence memory allocation logic. For environments where immediate patching is not feasible, administrators should restrict local access to the display server by enforcing strong authentication policies and limiting which users are permitted to connect via X11 forwarding or direct console sessions. Additionally, deploying intrusion detection systems that monitor for anomalous behavior in shared memory segments associated with video overlays can provide an additional layer of defense against exploitation attempts targeting this specific weakness.