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How CVE-2026-49790 Works
CVE-2026-49790 is a high-severity elevation of privilege vulnerability residing in the Windows Universal Disk Format File System Driver (UDFS). The UDFS driver is a core Windows component responsible for parsing and handling UDF file systems, which are commonly found on optical media like DVDs and Blu-ray discs, as well as some removable storage devices. The vulnerability is rooted in two critical memory safety issues: a heap-based buffer overflow (CWE-122) and an integer underflow (CWE-191).
An integer underflow occurs when a calculation produces a value lower than the minimum allowable integer. If this underflowed value wraps around to a large positive number, it can be subsequently used for memory allocation or length validation. This creates a situation where the system allocates an insufficient buffer size. When the driver later writes data to this undersized heap buffer, it triggers a heap-based buffer overflow.
The attack vector for this vulnerability is strictly local. An attacker must already have some level of access to the target system and either convince a user to mount a maliciously crafted UDF file system or find a way to have the vulnerable driver process attacker-controlled data. The CVSS vector is AV:L/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:H. This means the attack requires low privileges to execute, has low complexity, but crucially, requires user interaction. A successful exploit would allow the attacker to execute arbitrary code with SYSTEM-level privileges, leading to a complete compromise of confidentiality, integrity, and availability. The vulnerability affects a wide range of Windows versions, including Windows 10, Windows 11, and Windows Server.
DailyCVE Form
Platform: Windows OS
Version: 10/11/Server
Vulnerability: Heap Overflow
Severity: High (7.3)
Date: 2026-07-14
Prediction: Already Patched
What Undercode Say: Analytics
Exploit Feasibility: Currently No Public PoC.
SSVC: Exploitation: none.
Automatable: No.
Technical Impact: Total.
Exploit
To trigger the vulnerability, an attacker would need to craft a malicious UDF file system image. Upon mounting or accessing this crafted volume, the vulnerable UDFS driver (typically udfs.sys) processes malformed metadata, triggering the integer underflow and subsequent heap overflow. The following command can be used to mount a potentially malicious ISO/UDF image, which would be the typical vector for exploitation:
Example: Mounting a malicious UDF image (attacker-controlled) powershell -command "Mount-DiskImage -ImagePath 'C:\path\to\malicious.udf'"
Note: The exact technical details of the exploit chain and the specific UDF structures involved have not been publicly disclosed by Microsoft as of the publication date.
Protection
Primary Mitigation: Apply the July 2026 cumulative security updates released by Microsoft on July 14, 2026. This is the only complete and confirmed fix for the vulnerability. Ensure systems are updated to the fixed build versions.
Workarounds & Configuration:
- Restrict the ability to mount removable media or optical disc images to only trusted users and processes.
- Implement application control policies (e.g., Windows Defender Application Control) to prevent untrusted drivers from loading.
- Exercise caution when mounting UDF file systems from untrusted or unknown sources.
Impact
Successful exploitation of CVE-2026-49790 leads to Elevation of Privilege to the SYSTEM level. This grants an attacker complete control over the affected system, enabling them to:
– Read sensitive system and user data (Confidentiality impact: High).
– Modify system files, install persistent malware, or backdoors (Integrity impact: High).
– Disable security software, disrupt operations, or cause a system crash (Availability impact: High).
This vulnerability is a critical component of the attack chain, often used as a second-stage exploit to gain full system privileges after an initial compromise.
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Sources:
Reported By: nvd.nist.gov
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