Attack Chain

1. An attacker sets up and operates a malicious RFB/VNC server.
2. A legitimate client application, utilizing GStreamer's rfbsrc plugin, is induced (e.g., via social engineering or compromised legitimate server redirection) to connect to the attacker's malicious RFB/VNC server.
3. Upon connection, the malicious server advertises a 16 bits per pixel (16bpp) framebuffer configuration to the connecting client.
4. The malicious server then sends specially crafted Hextile-encoded updates to the client.
5. The GStreamer rfbsrc plugin processes these updates, and its Hextile background fill path attempts to handle the pixel data.
6. The rfbsrc plugin writes 32-bit pixel values from the Hextile updates into a memory buffer that was incorrectly allocated for 16-bit pixels due to the advertised framebuffer configuration.
7. This type mismatch results in an out-of-bounds heap write, corrupting memory outside the intended buffer.
8. The out-of-bounds write leads to an immediate crash of the client application, resulting in a denial of service. Potential memory corruption may also occur, which could theoretically be leveraged for further exploitation.

Impact

Successful exploitation of CVE-2026-59691 leads to the crash of any client application utilizing the vulnerable GStreamer rfbsrc plugin when connecting to a malicious RFB/VNC server. This results in a complete denial of service for the affected application, making it unusable. While the primary impact is a crash, the out-of-bounds write can also lead to memory corruption, which could potentially be leveraged by an attacker to achieve more severe consequences, such as arbitrary code execution, though this is not explicitly confirmed by the source. This vulnerability directly impacts systems running Red Hat Enterprise Linux 6, 7, 8, 9, and 10, affecting the stability of applications relying on GStreamer for VNC connectivity.

Recommendation

• Patch CVE-2026-59691 by updating GStreamer packages (specifically gstreamer1-plugins-bad-free and gstreamer-plugins-bad-free) on all affected Red Hat Enterprise Linux systems to the versions provided by Red Hat.
• Implement network segmentation and strict outbound firewall rules to limit client workstation connections to only trusted and legitimate RFB/VNC servers, thereby minimizing exposure to malicious servers that could exploit CVE-2026-59691.