CVE-2019-1315

What is Windows Error Reporting?

Windows Error Reporting (WER) is the built-in Windows service that collects diagnostic information and crash dumps when applications or the operating system fail, and can run with SYSTEM privileges to gather data across process boundaries. Because it performs privileged file operations (writing and manipulating crash-dump and log files) triggered by ordinary application crashes — something any local user can cause — a flaw in how it handles those files is a reliable path from standard user to SYSTEM.

Overview

CVE-2019-1315 is a privilege escalation vulnerability in the Windows Error Reporting manager caused by improper handling of hard links. A local, low-privileged attacker can plant a hard link where WER expects to write a temporary or diagnostic file, causing the SYSTEM-privileged service to overwrite an attacker-chosen target file instead — Microsoft's own advisory notes that successful exploitation lets an attacker overwrite a targeted file, an action that can then be leveraged into elevated code execution.

Technical Details

The root cause (CWE-59, improper link resolution before file access) follows the well-established Windows hard-link privilege-escalation pattern seen across several 2019 CVEs: WER checks a file path it expects to control exclusively, but does not adequately verify — at the moment it performs the privileged write or delete — that the path hasn't been replaced with a hard link pointing at a protected system file. Since ordinary users can trigger WER activity simply by causing an application to crash, and the attacker fully controls the race window and the substituted link, winning the race allows the attacker to have SYSTEM overwrite an arbitrary file, which can then be weaponized (e.g., overwriting a file that will later be executed with elevated privileges) into full code execution as SYSTEM. Exploitation requires only local access, low privileges, and no user interaction.

Discovery

Microsoft addressed this bug through its own security response process ahead of the October 2019 Patch Tuesday, as part of a broader wave of hard-link-based privilege-escalation fixes to Windows servicing and reporting components throughout 2019; no specific outside researcher is publicly credited for this individual CVE.

Exploitation Context

CISA's KEV catalog listing confirms real-world exploitation, and the ransomwareUse: true designation indicates this bug has been observed used by ransomware-affiliated attackers as a local privilege-escalation step to reach SYSTEM following an initial, lower-privileged foothold — a very common post-exploitation pattern given how trivially WER activity can be triggered by any local user.

Remediation

1. Apply the October 2019 (or later) Windows cumulative update, which fixes WER's hard-link handling.
2. Prioritize patching broadly, since exploitation requires only the ability to run code locally and cause an ordinary application crash.
3. Deploy EDR tooling capable of detecting suspicious hard-link creation targeting WER's working directories or unexpected privileged file overwrites.
4. Limit local logon and standard-user software execution privileges where feasible to reduce the population capable of staging this exploit.
5. Review endpoint logs for unexpected SYSTEM-context file modifications correlated with application-crash and WER activity on unpatched hosts.