CVE-2026-109833 in Red Hat
Summary
by MITRE • 10/13/2026
A flaw was found in gnome-remote-desktop as shipped in Red Hat Enterprise Linux. In the VNC TLS read path, partial consumption of the internal peek buffer incorrectly moves remaining peeked bytes into the caller-supplied buffer instead of compacting the peek buffer. A remote attacker who can reach an enabled VNC TLS listener and trigger a peek/read size mismatch can cause an out-of-bounds write, leading to denial of service.
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Analysis
by VulDB Data Team • 10/13/2026
The vulnerability identified in gnome-remote-desktop within Red Hat Enterprise Linux represents a critical memory management error located specifically within the Virtual Network Computing (VNC) Transport Layer Security (TLS) read path. This flaw stems from an incorrect handling of internal buffer operations when processing incoming data streams. Specifically, the software utilizes an internal peek buffer to manage partial reads or look-ahead operations on encrypted network traffic. Under normal operational conditions, this mechanism ensures that data is correctly sequenced and processed without corrupting memory structures. However, a logical error exists in how remaining bytes are handled after a partial consumption event occurs within this buffered stream.
The core technical flaw involves the mismanagement of byte movement during read operations where there is a mismatch between the requested peek size and the actual amount of data consumed or available. Instead of correctly compacting the internal peek buffer to maintain contiguous memory integrity, the flawed logic incorrectly moves remaining peeked bytes directly into a caller-supplied buffer. This operation assumes that the destination buffer has sufficient allocated space and alignment compatible with the source data layout. Because this assumption is not validated against actual bounds, the write operation proceeds without proper boundary checks relative to the underlying heap or stack allocation limits.
This logic error results in an out-of-bounds write condition when a remote attacker can interact with an enabled VNC TLS listener and deliberately trigger conditions that cause a peek-read size mismatch. By crafting specific network packets that exploit this discrepancy, an attacker can force the application to write data beyond the allocated memory boundaries of the target buffer. The immediate operational impact of such a memory corruption event is typically a denial of service, as the out-of-bounds write corrupts adjacent memory structures, leading to application crashes or instability in the remote desktop session. In more severe scenarios involving sophisticated exploitation techniques, this could potentially lead to arbitrary code execution if an attacker can precisely control the data written and target critical function pointers or return addresses within the corrupted memory space.
From a classification perspective, this vulnerability aligns with CWE-787: Out-of-bounds Write, which describes writing data outside of intended boundaries, leading to undefined behavior and potential security breaches. Furthermore, in the context of attack tactics, this flaw facilitates exploitation techniques associated with ATT&CK T1059: Command and Scripting Interpreter or potentially lateral movement via remote services if the service is exposed externally. The vulnerability highlights risks inherent in complex network protocol implementations where buffer management logic becomes overly intricate across multiple layers such as TLS decryption and application-level parsing.
Mitigation strategies should prioritize immediate patching of gnome-remote-desktop to versions that include fixes for this specific buffer handling logic. Administrators must ensure that VNC services are not exposed directly to untrusted networks or the public internet without robust access controls, firewalls, or VPN tunnels restricting connectivity to authorized users only. Additionally, implementing strict input validation and ensuring that all read operations verify available data against destination buffer capacities can prevent similar issues in future updates. Regular security audits of remote desktop implementations and adherence to secure coding standards regarding memory management are essential for maintaining the integrity of enterprise Linux environments relying on these graphical subsystems.