CVE-2026-59691
Description
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.
Statement
This vulnerability is rated as Important severity because it is a heap out-of-bounds write reachable over the network, though exploitation requires user interaction (connecting to a malicious VNC server). The rfbsrc plugin is shipped as part of gstreamer1-plugins-bad-free in Red Hat Enterprise Linux 8, 9, 10, and Red Hat In-Vehicle Operating System (RHIVOS). A user must actively connect a GStreamer pipeline to a malicious RFB/VNC server to trigger this vulnerability. Code execution has not been demonstrated but cannot be ruled out for heap overflows. This is in the same code area as CVE-2026-52720, a few lines further down.
Mitigation
There is no complete mitigation for this vulnerability. The following measures can reduce risk:
1. Do not connect GStreamer pipelines using rfbsrc to untrusted or unknown VNC servers.
2. If the rfbsrc plugin is not required, remove the librfb plugin shared object from the GStreamer plugins directory (typically /usr/lib64/gstreamer-1.0/libgstrfbsrc.so).
3. Network-level controls (firewall rules) can restrict outbound VNC connections to trusted servers only.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 7.1 | N/A | 7.1 |
| Attack Vector | Network | N/A | Network |
| Attack Complexity | Low | N/A | Low |
| Privileges Required | None | N/A | None |
| User Interaction | Required | N/A | Required |
| Scope | Unchanged | N/A | Unchanged |
| Confidentiality | None | N/A | None |
| Integrity Impact | Low | N/A | Low |
| Availability Impact | High | N/A | High |
Vector
Red Hat: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:H
cve.org: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:H
Red Hat CVSS v3 Score Explanation
AV:N - RFB/VNC is network-accessible. AC:L - straightforward trigger with crafted Hextile frame. PR:N - no auth required on VNC server side. UI:R - victim must connect to malicious server. S:U - stays within GStreamer process. C:N - no data leak demonstrated. I:L - heap corruption possible but limited control. A:H - reliable crash.
Understanding the Weakness (CWE)
Integrity
Technical Impact: Modify Memory; Execute Unauthorized Code or Commands
Write operations could cause memory corruption. In some cases, an adversary can modify control data such as return addresses in order to execute unexpected code.
Availability
Technical Impact: DoS: Crash, Exit, or Restart
Attempting to access out-of-range, invalid, or unauthorized memory could cause the product to crash.
Other
Technical Impact: Unexpected State
Subsequent write operations can produce undefined or unexpected results.
Acknowledgements
Red Hat would like to thank Clouditera Security (Clouditera), NSFOCUS (NSFOCUS), and Z.ai Security (Z.ai) for reporting this issue.
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