Full Report
Introduction Microsoft Windows Graphics Device Interface+, also known as GDI+, allows various applications to use different graphics functionality on video... The post Analyzing CVE-2021-1665 – Remote Code Execution Vulnerability in Windows GDI+ appeared first on McAfee Blog.
Analysis Summary
# Vulnerability: GDI+ Remote Code Execution Vulnerability
## CVE Details
- CVE ID: CVE-2021-1665
- CVSS Score: Not explicitly mentioned in the text, but implied high severity due to RCE potential. (Severity: Likely High/Critical)
- CWE: Not explicitly mentioned, but related to improper input validation/logic errors in memory handling.
## Affected Systems
- Products: Microsoft Windows components leveraging GDI+ (Graphics Device Interface Plus).
- Versions: Unspecified specific vulnerable versions, but any system running Windows versions prior to the January 2021 patch.
- Configurations: Any application using GDI+ which calls the `GetThumbnailImage` API or processes specially crafted EMF image files containing `EmfPlusDrawString` records.
## Vulnerability Description
The vulnerability is a logic error within the Windows GDI+ component, specifically triggered while processing certain records within an Enhanced Metafile (EMF) file, likely during thumbnail generation via the `GetThumbnailImage` API or processing `EmfPlusDrawString` records. The flaw resides in how the program handles the return value of the function `gdiplus!BuiltLine::GetUntrimmedCharacterCount`. When this function returns 0, the control flow executes one extra iteration of a loop than intended, leading to incorrect register values (specifically `ECX` controlling the loop count) and subsequent memory corruption (indicated by reading from an address pointed to by `edx+8` where `edx` held `c0c0c0c0`). This results in an application crash, which is the precursor to remote code execution (RCE).
## Exploitation
- Status: PoC available (The research detailed the creation and testing of a PoC using WinAFL).
- Complexity: Low to Medium (Requires crafting a specific malicious EMF file and triggering GDI+ processing, which happens easily if thumbnail generation is used).
- Attack Vector: Network (via malicious file attachment/download) or Local (via malicious file processing).
## Impact
- Confidentiality: High (If RCE is achieved)
- Integrity: High (If RCE is achieved)
- Availability: High (Denial of Service via crash)
## Remediation
### Patches
- Microsoft released a patch addressing this issue in **January 2021**. Users should ensure their Windows deployment is fully updated to receive the fix applied to `gdiplus.dll`.
### Workarounds
- The text implies that applying the official patch is the definitive remediation. No specific configuration workarounds are detailed, but limiting application exposure to untrusted EMF files or disabling GDI+ processing in high-risk contexts would serve as theoretical mitigations if patching were impossible.
## Detection
- Indicators of Compromise: Crashes occurring within GDI+ functions such as `gdiplus!BuiltLine::GetBaselineOffset` while processing image data or thumbnail generation requests. Register values used in the crash analysis (`edx` containing `c0c0c0c0`) might be indicative, especially if page heap is enabled.
- Detection methods and tools: Standard Windows crash dump analysis tools (like WinDbg) focused on analyzing crashes within `gdiplus.dll` when processing application input files (e.g., images).
## References
- Vendor Advisory: Microsoft's January 2021 Security Update (Details not linked).
- Research Link: Documented analysis by McAfee. (URL provided in source material: `https://docs.microsoft.com/en-us/openspecs/windows_protocols/ms-emfplus/07bda2af-7a5d-4c0b-b996-30326a41fa57` - This link points to GDI+ specification, not the advisory itself).