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How CVE-2026-58609 Works
CVE-2026-58609 is a high‑severity vulnerability in the Microsoft Windows Graphics Component that arises from an out‑of‑bounds read (CWE‑125) during the processing of specially crafted graphics content. The flaw resides in the way the component handles Enhanced Metafile (EMF) records – specifically, records such as `EMR_STRETCHDIBITS` or `EMR_BITBLT` that carry embedded `BITMAPINFOHEADER` structures.
Under normal operation, the graphics engine parses these structures to determine bitmap dimensions, colour depth, and palette information. However, a boundary condition exists when the `biClrUsed` or `biWidth` fields are manipulated with excessively large or corrupted values. In one documented code path, the `MfEnumState::OutputDIB()` function miscalculates the size of the `BITMAPINFO` structure because it trusts a corrupted `iUsageSrc` field (e.g. 0x20000b1), leading to an incorrect memory size calculation. Subsequently, a `memcpy()` or internal read operation attempts to access memory beyond the allocated buffer, reading data past the end of the intended structure.
The vulnerability is locally exploitable (AV:L) and requires user interaction (UI:R) – an attacker must convince a victim to open a malicious file (e.g. an email attachment, a downloaded document, or a file shared via collaboration platforms). The attack does not require prior privileges (PR:N) and has low complexity (AC:L). Once triggered, the out‑of‑bounds read can be leveraged to read sensitive memory contents, which may include credentials, cryptographic keys, or other process data. Under specific conditions, Microsoft has confirmed that this information disclosure can be chained into arbitrary code execution (RCE), compromising confidentiality, integrity, and availability (C:H/I:H/A:H).
The CVSSv3.1 base score is 7.8 (High), with the vector AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H. Microsoft released fixes as part of the July 14, 2026 cumulative updates for all supported Windows client and server versions. At the time of disclosure, no public exploitation had been observed, and the flaw was not known to be used in active attacks. However, the potential for remote code execution makes it a critical priority for patching.
DailyCVE Form
| Field | Details |
|–|-|
| Platform | Microsoft Windows |
| Version | Windows 10 (1607, 1809, 21H2, 22H2), Windows 11 (24H2, 25H2, 26H1), Windows Server (2012, 2012 R2, 2016, 2019, 2022, 2025) |
| Vulnerability | Out‑of‑bounds Read (CWE‑125) |
| Severity | High (CVSS 7.8) |
| Date | 2026‑07‑14 |
| Prediction | Patch already released (July 14, 2026) |
What Undercode Say
Analytics
- EPSS Score: Not yet available (pending enrichment)
- Exploitability: Easy (low complexity, no privileges required)
- Automatable: No (CISA ADP assessment)
- Technical Impact: Total (full compromise of confidentiality, integrity, and availability)
- Current Exploit Price (est.): $5k – $25k (as of July 14, 2026)
- CTI Interest Score: 0.69 (elevated attacker interest)
Bash Commands & Codes
Check if the Windows system is missing the July 2026 cumulative update (PowerShell):
Get-HotFix | Where-Object { $<em>.HotFixID -like "KB" -and $</em>.InstalledOn -lt "2026-07-14" }
Query the specific build number to verify patch level (CMD):
wmic os get buildnumber
Compare against the fixed versions:
- Windows 10 1809: `10.0.17763.9020` or higher
- Windows 11 24H2: `10.0.26100.8875` or higher
- Windows Server 2025: `10.0.26100.33158` or higher
Simulate the out‑of‑bounds condition (conceptual Python snippet – for educational use only):import struct Craft a malicious BITMAPINFOHEADER with oversized biClrUsed bmih = struct.pack('<IIIIIIIIII', 0x28, biSize 0x901, biWidth (large) 0x1, biHeight 0x1, biPlanes 0x1, biBitCount 0x0, biCompression 0x4, biSizeImage 0x0, biXPelsPerMeter 0x0, biYPelsPerMeter 0xFFFFFFFF, biClrUsed (corrupted) 0x0 biClrImportant ) This structure, when parsed by the vulnerable OutputDIB(), triggers an oversized read.Exploit
An attacker crafts a malicious EMF or WMF file containing a `BITMAPINFOHEADER` with a manipulated `biClrUsed` or `biWidth` value. The file is delivered via email, instant messaging, or a compromised website. When the victim opens the file (e.g., in Windows Photo Viewer, Office applications, or any software that uses the Graphics Component), the vulnerable `MfEnumState::OutputDIB()` or `EmfEnumState::CreateModifiedDib()` function miscalculates the buffer size and reads out‑of‑bounds. This read can disclose kernel or process memory, and with further exploitation (e.g., heap grooming), an attacker can achieve arbitrary code execution under the context of the affected application. If the application runs with elevated privileges, the attacker gains full system control.
Protection
- Apply the July 2026 cumulative updates immediately (KB5012170 or later for your Windows version).
- Restrict file types – block untrusted EMF/WMF files at email gateways and web proxies.
- User awareness – train users not to open attachments from unknown sources.
- Enable Windows Defender Exploit Guard – enable “Block untrusted fonts” and “Protect against potentially unwanted applications”.
- Run applications with least privilege – avoid using administrator accounts for routine tasks.
- Monitor for suspicious graphics‑processing activity using Sysmon or EDR solutions.
Impact
– Confidentiality: An attacker can read sensitive memory contents, potentially exposing passwords, encryption keys, or intellectual property.
– Integrity: The out‑of‑bounds read can be combined with other techniques to modify memory and execute arbitrary code, altering system or application behaviour.
– Availability: Successful code execution can lead to system crashes, denial of service, or complete takeover of the affected host.
– Scope: The vulnerability is confined to the security context of the vulnerable component (Scope: Unchanged), but if that component runs with high privileges, the impact is system‑wide.
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Sources:
Reported By: nvd.nist.gov
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