CVE-2026-57965: spice-vdagent Denial of Service Vulnerability

CVE-2026-57965 Overview

A flaw exists in spice-vdagent, the guest-side daemon that facilitates communication between a virtual machine and its SPICE host. A malicious or compromised SPICE host can send a specially crafted message that triggers an integer overflow [CWE-190] in the daemon. The overflow leads to a heap buffer overflow condition, causing spice-vdagent to crash. The resulting crash produces a Denial of Service (DoS) inside the affected virtual machine. Exploitation requires the SPICE host to be untrusted or already compromised, limiting the practical attack surface to environments where guest-host trust boundaries are inverted.

Critical Impact
A compromised SPICE host can crash the spice-vdagent daemon inside guest virtual machines, producing a Denial of Service condition for VM clipboard, file transfer, and display integration features.

Affected Products

spice-vdagent (guest agent component of the SPICE remote display protocol)
Red Hat Enterprise Linux distributions shipping affected spice-vdagent builds
Virtualization environments using SPICE for guest-host integration

Discovery Timeline

2026-06-29 - CVE-2026-57965 published to NVD
2026-06-29 - Last updated in NVD database

Technical Details for CVE-2026-57965

Vulnerability Analysis

The vulnerability resides in the message-parsing logic of spice-vdagent, the guest daemon that handles SPICE protocol messages from the host. When the daemon processes a specially crafted message, an arithmetic operation on attacker-controlled length or size fields overflows the bounds of its integer type. The overflowed value is then used to allocate or index into a heap buffer, producing a heap buffer overflow. The corrupted allocation causes the daemon to crash, terminating guest-side SPICE integration features such as shared clipboard, drag-and-drop, and dynamic resolution adjustment.

The issue is classified as an Integer Overflow to Buffer Overflow chain under [CWE-190]. The attack vector is local to the virtualization stack, and exploitation requires high privileges on the SPICE host side. Impact is limited to availability of the spice-vdagent process; confidentiality is not affected, and integrity impact is low.

Root Cause

The root cause is missing or insufficient validation of size-related fields in SPICE messages before they participate in arithmetic used for heap allocation. When the computed size wraps around, the daemon allocates a buffer smaller than intended and subsequently writes past its bounds.

Attack Vector

Exploitation requires a malicious or compromised SPICE host. The host sends a crafted SPICE message to the guest, where spice-vdagent parses it and triggers the overflow. This inverts the usual trust model: normally the host is trusted by the guest. The bug therefore matters most in multi-tenant or nested virtualization scenarios where the host cannot be fully trusted by the guest workload.

No verified proof-of-concept code is publicly available. See the Red Hat CVE-2026-57965 Advisory and Red Hat Bugzilla Report #2493581 for technical details.

Detection Methods for CVE-2026-57965

Indicators of Compromise

Unexpected termination or repeated crashes of the spice-vdagent daemon inside guest VMs.
Core dumps or systemd service failure events referencing spice-vdagent or spice-vdagentd.
Sudden loss of SPICE integration features such as shared clipboard or dynamic display resizing within a running guest.

Detection Strategies

Monitor journalctl -u spice-vdagentd and /var/log/messages for abnormal exit codes, SIGSEGV signals, or heap corruption diagnostics.
Correlate guest-side daemon crashes with anomalous SPICE host activity or unauthorized host-level changes.
Track package versions of spice-vdagent across the guest fleet to identify hosts running unpatched builds.

Monitoring Recommendations

Enable systemd-coredump on guests running spice-vdagent to capture crash artifacts for forensic review.
Alert on repeated restarts of spice-vdagentd.service within short time windows.
Audit which virtualization hosts are considered trusted and flag guests running on multi-tenant or externally managed hypervisors.

How to Mitigate CVE-2026-57965

Immediate Actions Required

Apply vendor-provided updates for spice-vdagent as soon as patched packages are available from your Linux distribution.
Restrict which SPICE hosts guests will connect to, and validate the integrity of hypervisor hosts.
Where SPICE integration is not required, disable or remove spice-vdagent from guest images to eliminate the attack surface.

Patch Information

Refer to the Red Hat CVE-2026-57965 Advisory for the authoritative list of fixed package versions. Track upstream spice-vdagent commits and rebuild or update distribution packages once fixed builds are published. Verify the installed version with rpm -q spice-vdagent or the equivalent package manager query for your distribution.

Workarounds

Stop and disable the daemon on guests that do not require SPICE integration using systemctl disable --now spice-vdagentd.service.
Limit deployment of SPICE-enabled guests to environments with fully trusted, tightly controlled hypervisor hosts.
Isolate untrusted hypervisor tenants from guests that require high availability of clipboard and display integration features.

bash

# Disable spice-vdagent on guests where SPICE integration is not required
sudo systemctl disable --now spice-vdagentd.service
sudo systemctl mask spice-vdagentd.service

# Verify installed package version after patching
rpm -q spice-vdagent