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Welcome to December 2025’s Patch Tuesday!
As your team starts to wind down for the holidays, attackers often speed up, taking advantage of reduced staffing and seasonal distractions.
Below, you’ll find the key issues to understand before heading into the new year. If you want the full conversation, listen to the latest episode of Patch Fix Tuesday.
CVE-2025-55182 [Critical]
React2Shell
CVE-2025-55182 (CVSS 10/10) is a remote code execution vulnerability in React Server Components. The issue stems from how serialized data travels between the server and client. When this data reaches the server again, the deserialization path can be manipulated. An attacker who sends a crafted payload can trigger server-side code execution.
This attack requires no authentication, which makes any internet-facing service using affected components an attractive target. Even teams that don’t consider themselves “React users” may still run vulnerable server components bundled inside other packages. That hidden dependency risk raises the stakes, especially during a period when many systems run unattended.
How attackers exploit this vulnerability
Send crafted serialized payloads that trigger remote code execution during server deserialization
Target servers that unknowingly bundle React Server Components through third-party libraries
Scan the internet for endpoints exposing unpatched versions
What to look out for
Unexpected alerts tied to React Server Components despite limited frontend use
Broad detections that flag exposure without clear evidence
Suspicious inbound traffic attempting serialized payload injection
Mitigation guidance
Identify whether React Server Components exist anywhere in your environment, even indirectly
Review both frontend and backend dependencies to confirm version coverage
Update any framework or library bundling RSC to 1901, 1912, 1921 or later, which remove the vulnerable code path
Validate findings from automated scanning tools and confirm true exposure before triage
– Ryan Braunstein, Security Manager, Automox
CVE-2025-62550 [Important]
Azure Monitor Agent Remote Code Execution Vulnerability
CVE-2025-62550 is a remote code execution flaw in the Azure Monitor Agent with a CVSS 8.8/10. The vulnerability abuses the syslog user, leveraging whatever permissions that account already has. If the syslog user can write to specific locations or interact with sensitive processes, an attacker may use this role to move across the system while blending into routine operational activity.
This vulnerability is notable because attackers often target log pipelines when trying to hide activity. Access through a log-related service gives them both an entry point and the chance to mask their actions.
How attackers may exploit this vulnerability
Execute commands under the syslog user to remain less visible
Delete or alter log data to obscure incident timelines
Enumerate server configurations when the syslog user has read-only access
Use “living off the land” techniques to blend with normal monitoring workflow by exploiting built-in system utilities instead of using external tools
Chain the exploit with other RCE or privilege escalation paths
What to look out for
Gaps or corruption in server logs
Unexpected syslog-related process activity
Host telemetry showing reconnaissance actions from low-privilege accounts
Mitigation guidance
Confirm the version of Azure Monitor Agent deployed across your estate
Harden or restrict the syslog user wherever possible
Review log integrity and monitoring pipelines for anomalies
Apply Microsoft’s security update once validated in your environment
– Mat Lee, Senior Security Engineer, Automox
CVE-2025-62565 [Important]
Windows File Explorer Elevation of Privilege Vulnerability
CVE-2025-62565 is an elevation-of-privilege bug in Windows File Explorer with a CVSS 7.3/10. It originates from a use-after-free condition inside the Windows shell. When File Explorer interacts with a file – such as loading an icon, reading metadata, or generating a preview – it may re-use memory that has already been freed. A malicious file designed to exploit this timing can trigger code execution at a higher privilege level.
While Microsoft lists user interaction as required, the bar for interaction is extremely low. A single click (or hover) to select a file, not open it, could potentially trigger the vulnerable code path.
How attackers exploit this vulnerability
Deliver a crafted file through phishing or removable media that triggers the use-after-free condition
Gain system-level privileges after an initial foothold to expand control across the device
Target preview or metadata operations that run without fully opening a file
What to look out for
Suspicious files delivered through phishing or user-to-user sharing
End users reporting unexpected WIndows File Explorer behavior when selecting files
Alerts tied to shell or preview-related crashes or memory faults
Mitigation guidance
Review Microsoft’s security update and deploy across supported Windows versions
Validate whether preview operations are required for your environment’s workflows
Reinforce phishing awareness, especially during the holiday season
Monitor for privilege escalations that originate from Explorer or shell-related processes
– Seth Hoyt, Senior Security Engineer, Automox
Patch regularly, patch often
Consistent patching gives you a reliable path to reducing exposure across your environment. Each month brings new risk, but steady, automated updates limit the time attackers have to act. Strong patching practices also support broader security hygiene such as monitoring, training, and incident readiness.
As this year closes, use the quieter weeks to confirm your policies, strengthen detection, and enter January with confidence.
Until next month: Patch regularly, patch often.
