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How CVE-2026-54995 Works
The vulnerability resides in the Reliable Multicast Transport Driver (rmcast.sys), a kernel-mode component responsible for handling reliable multicast communication in Microsoft Windows. This driver is used in enterprise environments, industrial control systems, and real-time communication platforms where multicast traffic is prevalent.
CVE-2026-54995 is a use-after-free (CWE-416) memory corruption flaw. The driver allocates memory buffers to process incoming multicast packets. Under specific, crafted network conditions, the driver can free a memory region while still holding a reference (pointer) to it. Subsequently, the driver attempts to access that freed memory—either to read data or to call a function pointer stored there.
An attacker can exploit this by sending a carefully constructed sequence of multicast packets over the network. This triggers the vulnerable code path in rmcast.sys, causing the driver to release memory resources prematurely. The attacker then races to reuse the freed memory with attacker-controlled data (e.g., a malicious payload or a fake function table) before the driver accesses it. When the driver subsequently dereferences the stale pointer, it executes the attacker’s code with kernel-level privileges.
The attack is initiated remotely over the network without requiring any authentication or user interaction. However, the attacker must be network-adjacent—meaning they need to be on the same local network segment or have the ability to send multicast traffic to the target. The exploitation is considered easy, and while no public exploit is currently available, the exploit price is estimated between $25,000 and $100,000. Successful exploitation leads to complete compromise of confidentiality, integrity, and availability (C:I:A:H).
DailyCVE Form
Platform: ……. Windows
Version: …….. 10/11/Server
Vulnerability :.. Use-After-Free
Severity: ……. 8.1 High
date: ………. 2026-07-14
Prediction: ….. 2026-08-11
What Undercode Say
Analytics:
- CVSS Base Score: 8.1 (High) – Vector: `CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H`
– Exploit Price (est.): $25k–$100k - SSVC Exploitation: none; Automatable: no; Technical Impact: total
- Affected Products: Windows 10 v1607, v1809, v21H2, v22H2; Windows 11 v24H2, v25H2, v26H1; Windows Server 2025 (and likely earlier Server versions)
- Patch Availability: Included in the July 2026 Patch Tuesday update (KB5089549 and related cumulative updates)
Bash Commands & Codes:
Check if the system is vulnerable by verifying rmcast.sys version
Get-ItemProperty -Path "C:\Windows\System32\drivers\rmcast.sys" | Select-Object VersionInfo
Alternative: Use certutil to compute the driver hash for integrity verification
certutil -hashfile C:\Windows\System32\drivers\rmcast.sys SHA256
Query the installed Windows update to confirm patch status
Get-HotFix | Where-Object { $<em>.HotFixID -like "KB5089549" }
Network monitoring: Detect anomalous multicast traffic (using Wireshark/tshark)
tshark -i eth0 -Y "ip.dst == 224.0.0.0/4 and (udp.port == 5004 or udp.port == 5005)" -T fields -e ip.src -e ip.dst -e udp.length
Use PowerShell to list all network interfaces and their multicast group memberships
Get-NetIPInterface | Where-Object { $</em>.MulticastForwarding -eq "Enabled" }
Exploit
The exploitation of CVE-2026-54995 follows a standard use-after-free pattern in a kernel driver:
1. Trigger the Free: An attacker sends a specially crafted sequence of multicast packets that causes the `rmcast.sys` driver to release a specific memory object (e.g., a multicast session context or packet buffer) prematurely.
2. Reclaim the Memory: The attacker then rapidly sends another set of packets that cause the kernel to allocate new data into the same freed memory region. This new data is attacker-controlled and can include shellcode or a fake function table.
3. Dereference the Stale Pointer: The driver later attempts to use the original (now-stale) pointer to access what it believes is still valid data. Because the memory now holds attacker-controlled content, the driver executes the attacker’s payload at kernel privilege level.
4. Remote Code Execution: The payload can install a backdoor, escalate privileges, or pivot to other systems on the network. The attack requires no authentication and is performed entirely over the network, making it a potent vector for network-adjacent adversaries.
Protection
- Apply Patches Immediately: Install the July 2026 Patch Tuesday updates (specifically KB5089549 and any cumulative updates for your Windows version). This is the primary and most effective mitigation.
- Network Segmentation: Restrict multicast traffic to trusted network segments. Use firewall rules to block unnecessary multicast protocols (e.g., UDP ports 5004, 5005) at the network perimeter.
- Disable RMCAST if Unused: If your environment does not require reliable multicast, consider disabling the Reliable Multicast Transport Driver. This can be done via Device Manager or by disabling the associated network services.
- Enable Kernel Mitigations: Ensure that Address Space Layout Randomization (ASLR) and Data Execution Prevention (DEP) are enabled at the kernel level to increase the difficulty of exploitation.
- Monitor for Anomalous Traffic: Deploy intrusion detection systems (IDS) to monitor for unusual multicast patterns, especially from untrusted sources.
Impact
- Confidentiality: An attacker can read sensitive kernel memory, including passwords, encryption keys, and other system secrets.
- Integrity: The attacker can modify system files, install malware, or alter system configurations at the kernel level.
- Availability: The attacker can crash the system (BSOD) or cause denial of service by corrupting kernel data structures.
- Scope: Because the vulnerability exists in a network-facing kernel driver, a single successful exploit can compromise an entire network segment, affecting all systems that process multicast traffic.
- Risk to Enterprise: Organizations relying on multicast for critical operations (e.g., financial trading, industrial control, real-time collaboration) face elevated risk. Network-adjacent attackers (e.g., on public Wi-Fi or compromised internal networks) can exploit this without any user interaction.
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Sources:
Reported By: nvd.nist.gov
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