CVE-2026-59691 in Enterprise Linux 10
Summary
by MITRE • 07/09/2026
A heap buffer overflow vulnerability was found in GStreamer's rfbsrc plugin. When a client connects to a malicious RFB/VNC server that advertises a 16bpp framebuffer and sends Hextile-encoded updates, the Hextile background fill path writes 32-bit pixel values into a buffer allocated for 16-bit pixels. This type mismatch causes an out-of-bounds heap write that can lead to denial of service (process crash) and potential memory corruption.
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Analysis
by VulDB Data Team • 07/09/2026
This vulnerability resides within GStreamer's rfbsrc plugin, which handles remote frame buffer protocol connections typically used for VNC server communications. The flaw manifests when a malicious RFB/VNC server advertises a 16bpp framebuffer configuration while simultaneously sending Hextile-encoded screen updates. The Hextile encoding format supports various pixel depths including 16-bit and 32-bit modes, but the rfbsrc plugin fails to properly validate or handle this inconsistency during the background fill operation. When processing these updates, the plugin writes 32-bit pixel values into memory buffers that were allocated based on the advertised 16bpp configuration, creating a fundamental type mismatch that leads to heap memory corruption.
The technical implementation of this buffer overflow occurs in the Hextile background fill path where the plugin assumes all incoming pixel data matches the initially advertised framebuffer depth. This assumption breaks down when malicious servers send data with different bit depths, causing an out-of-bounds write operation that exceeds the allocated buffer boundaries. The heap memory corruption results from writing 32-bit values into 16-bit storage locations, effectively overwriting adjacent memory regions and potentially corrupting heap metadata structures. This type of vulnerability maps directly to CWE-121 Heap-based Buffer Overflow, which specifically addresses buffer overflows occurring in heap-allocated memory regions.
The operational impact of this vulnerability extends beyond simple denial of service conditions to include potential memory corruption that could enable more sophisticated attack vectors. While the immediate effect manifests as process crashes and system instability, the underlying heap corruption creates opportunities for attackers to manipulate program execution flow or execute arbitrary code depending on memory layout and exploitation conditions. The vulnerability affects any application using GStreamer's rfbsrc plugin when connecting to potentially malicious VNC servers, making it particularly concerning for remote desktop environments and security monitoring systems that rely on such components. This issue aligns with ATT&CK technique T1203 Exploitation for Client Execution, as it represents a classic buffer overflow exploit that could be leveraged for privilege escalation or system compromise.
Mitigation strategies should focus on input validation and proper bounds checking within the rfbsrc plugin implementation. The most effective approach involves implementing strict pixel depth verification before processing Hextile-encoded updates, ensuring that all incoming pixel data matches the configured framebuffer parameters. Additionally, developers should implement proper memory allocation techniques that account for potential bit depth variations in network protocols, including dynamic buffer sizing based on actual data requirements rather than advertised capabilities. Regular security updates and patch management procedures should be prioritized to address this class of vulnerability in GStreamer components, while network segmentation and access controls can help limit exposure to potentially malicious VNC servers in enterprise environments.