Bug 2493581 (CVE-2026-57965)

Summary: CVE-2026-57965 spice-vdagent: Integer overflow in udscs_write() leading to heap buffer overflow
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
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Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in spice-vdagent. A malicious or compromised SPICE host can trigger an integer overflow by sending a specially crafted message. This vulnerability can lead to a heap buffer overflow, causing the spice-vdagent daemon to crash and resulting in a Denial of Service (DoS) for the virtual machine. This issue requires the SPICE host to be untrusted or compromised for exploitation.
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Bug Depends On: 2494104    
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Description OSIDB Bzimport 2026-06-26 15:37:06 UTC 
An integer overflow vulnerability was found in spice-vdagent. In src/udscs.c, the udscs_write() function computes a buffer size as buf_size = sizeof(header) + size, where buf_size is a guint (unsigned 32-bit). When size is >= 0xFFFFFFF1 (since sizeof(header) is 16), this addition wraps to zero or a very small value. g_malloc(0) returns a valid tiny allocation (typically 1 byte), and the subsequent memcpy(buf + 16, data, size) writes approximately 4GB past the end of the buffer, causing a heap buffer overflow. This has been confirmed with AddressSanitizer (heap-buffer-overflow). On a normal (non-ASAN) build the daemon crashes with SIGBUS.

The trigger path is through VDAgentMessage.size in clipboard or file transfer messages from the SPICE host. The size validation at vdagentd.c:572 only checks >= min_size with no upper bound.

Note: exploitation requires a malicious or compromised SPICE host to send a crafted message with a large size field. In standard SPICE deployments, the host is trusted.