CVE-2026-109833 Overview
CVE-2026-109833 is an out-of-bounds write vulnerability in gnome-remote-desktop as shipped in Red Hat Enterprise Linux. The flaw resides in the Virtual Network Computing (VNC) Transport Layer Security (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 corrupt memory. Successful exploitation results in denial of service against the remote desktop daemon. The weakness is classified as [CWE-121] Stack-based Buffer Overflow.
Critical Impact
Remote unauthenticated attackers reachable to an enabled VNC TLS listener can trigger an out-of-bounds write, causing denial of service of the gnome-remote-desktop service.
Affected Products
- Red Hat Enterprise Linux gnome-remote-desktop package
- Deployments with the VNC TLS listener enabled
- Systems exposing the VNC TLS port to untrusted networks
Discovery Timeline
- 2026-10-13 - CVE-2026-109833 published to the National Vulnerability Database (NVD)
- 2026-10-15 - Last updated in NVD database
Technical Details for CVE-2026-109833
Vulnerability Analysis
The vulnerability resides in the VNC TLS read path of gnome-remote-desktop. The implementation maintains an internal peek buffer to support non-destructive reads from the TLS stream. When the caller consumes only a portion of the peeked data, the remaining peeked bytes should stay in the peek buffer, which should be compacted to reflect the consumed region.
Instead, the implementation copies the remaining peeked bytes into the caller-supplied buffer. When the caller buffer is smaller than the residual peek data, the copy writes past the end of the destination allocation. This produces an out-of-bounds write condition that corrupts adjacent memory and crashes the daemon.
Root Cause
The root cause is incorrect buffer accounting during partial consumption of peeked TLS data. The code treats the caller buffer as the destination for leftover peek bytes rather than compacting the internal peek buffer in place. No bounds check validates that the caller buffer can accommodate the residual data length, satisfying the conditions for [CWE-121].
Attack Vector
Exploitation requires network reachability to an enabled VNC TLS listener. The attacker establishes a TLS session and issues read requests crafted to induce a peek/read size mismatch, where the requested read size is smaller than the data previously peeked. The resulting out-of-bounds write terminates the service and interrupts active remote desktop sessions. No authentication or user interaction is required, though attack complexity is elevated due to the specific protocol state required to trigger the mismatch.
No public proof-of-concept code is available. Readers should consult the Red Hat CVE-2026-109833 Advisory and the Red Hat Bug Report #2550367 for additional technical context.
Detection Methods for CVE-2026-109833
Indicators of Compromise
- Unexpected crashes or restarts of the gnome-remote-desktop service with signals indicating memory corruption such as SIGSEGV or SIGABRT
- Core dumps or systemd-coredump events referencing gnome-remote-desktop and the VNC TLS read code path
- Anomalous TLS session patterns against the VNC listener involving short-lived connections and partial reads
Detection Strategies
- Monitor system journals for repeated termination events of gnome-remote-desktop and correlate with inbound VNC TLS connections
- Deploy network telemetry on the VNC TLS port to flag unusual peek/read sequences, truncated handshakes, or repeated connection attempts from a single source
- Enable crash reporting to capture stack traces that reference the VNC TLS read path for triage
Monitoring Recommendations
- Alert on systemd service failure events for gnome-remote-desktop.service with non-zero exit status
- Track volumes of inbound connections to the VNC TLS listener and baseline expected client sources
- Forward daemon logs and core dump metadata to a centralized data lake for retention and correlation
How to Mitigate CVE-2026-109833
Immediate Actions Required
- Apply vendor-provided updates for gnome-remote-desktop once released by Red Hat
- Restrict network exposure of the VNC TLS listener to trusted management networks only
- Disable the VNC TLS listener on hosts where remote desktop access is not required
Patch Information
At time of publication, consult the Red Hat CVE-2026-109833 Advisory for the current patch status and errata references. Track the Red Hat Bug Report #2550367 for fix availability across supported Red Hat Enterprise Linux versions.
Workarounds
- Block inbound traffic to the VNC TLS port at the host firewall using firewalld or nftables rules
- Require VPN or bastion-host access before any remote desktop connection reaches the listener
- Stop and mask the gnome-remote-desktop service on systems that do not require remote graphical access
# Configuration example
# Stop and mask the service on hosts that do not need remote desktop
sudo systemctl stop gnome-remote-desktop.service
sudo systemctl mask gnome-remote-desktop.service
# Restrict VNC TLS access to a trusted management subnet with firewalld
sudo firewall-cmd --permanent --zone=drop --add-source=0.0.0.0/0
sudo firewall-cmd --permanent --zone=trusted --add-source=10.10.0.0/24
sudo firewall-cmd --permanent --zone=trusted --add-port=5900/tcp
sudo firewall-cmd --reload
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
