CVE-2021-26237:FastStone Image Viewer 7.5 and earlier versions contain an out-of-bounds write vulnerability when processing malformed CUR files, potentially allowing for denial of service or code execution.

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FastStone Image Viewer version 7.5 and earlier contains a user mode write access violation vulnerability (CWE-787: Out-of-bounds Write) that occurs when processing malformed CUR cursor files. When a user opens or views a specially crafted CUR file, the application's FSViewer.exe process mishandles the file data, triggering a write access violation at memory address 0x00402d7d. This vulnerability could allow attackers to cause a denial of service condition by crashing the application or potentially achieve arbitrary code execution in the context of the current user.

Overview

This vulnerability affects FastStone Image Viewer, a popular image viewing and editing application for Windows. The issue stems from improper validation of CUR file formats, which are cursor files commonly used in Windows systems. When processing malformed CUR files, the application attempts to write data outside the bounds of allocated memory, resulting in an access violation. This type of memory corruption vulnerability is particularly concerning as it could potentially be exploited beyond just crashing the application, allowing attackers to execute arbitrary code if they can control the memory write operation. Users who open malicious CUR files received via email, downloaded from untrusted websites, or accessed through other means could be affected by this vulnerability.

Remediation

To mitigate this vulnerability, users should:

  1. Update FastStone Image Viewer to a version newer than 7.5 if available
  2. Exercise caution when opening CUR files from untrusted sources
  3. Consider using alternative image viewing software until a patch is available
  4. Implement standard security practices such as running applications with least privilege
  5. Consider using security software that can detect and block exploitation attempts

System administrators in enterprise environments should:

  1. Deploy application control policies to prevent execution of vulnerable versions
  2. Block CUR files from untrusted sources at email and web gateways
  3. Monitor for suspicious crashes of FSViewer.exe that might indicate exploitation attempts

References

  1. VoidSec Advisory: https://voidsec.com/advisories/cve-2021-26237-faststone-image-viewer-v-7-5-user-mode-write-access-violation/
  2. CWE-787: Out-of-bounds Write: https://cwe.mitre.org/data/definitions/787.html
  3. MITRE CVE Entry: CVE-2021-26237
  4. FastStone Image Viewer Official Website: https://www.faststone.org/

Industry ExposureMost to least
This section illustrates the prevalence of a specific Common Vulnerabilities and Exposures (CVE) across various industries based on customer reports. The ranking displays industries from the most to least affected by this particular vulnerability, offering valuable insight into where this CVE has been most frequently observed. This information can help organizations within these sectors prioritize their security efforts, understand their relative risk exposure compared to their peers, and focus remediation strategies where they are most needed. By understanding the industry-specific impact, organizations can make more informed decisions regarding patching, resource allocation, and overall risk management related to this CVE.

  1. Educational Services: Low
    Educational Services
  2. Manufacturing: Low
    Manufacturing
  3. Public Administration: Low
    Public Administration
  4. Finance and Insurance: Low
    Finance and Insurance
  5. Health Care & Social Assistance: Low
    Health Care & Social Assistance
  6. Management of Companies & Enterprises: Low
    Management of Companies & Enterprises
  7. Other Services (except Public Administration): Low
    Other Services (except Public Administration)
  8. Professional, Scientific, & Technical Services: Low
    Professional, Scientific, & Technical Services
  9. Retail Trade: Low
    Retail Trade
  10. Utilities: Low
    Utilities
  11. Accommodation & Food Services: Low
    Accommodation & Food Services
  12. Administrative, Support, Waste Management & Remediation Services: Low
    Administrative, Support, Waste Management & Remediation Services
  13. Agriculture, Forestry Fishing & Hunting: Low
    Agriculture, Forestry Fishing & Hunting
  14. Arts, Entertainment & Recreation: Low
    Arts, Entertainment & Recreation
  15. Construction: Low
    Construction
  16. Information: Low
    Information
  17. Mining: Low
    Mining
  18. Real Estate Rental & Leasing: Low
    Real Estate Rental & Leasing
  19. Transportation & Warehousing: Low
    Transportation & Warehousing
  20. Wholesale Trade: Low
    Wholesale Trade

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  1. See Everything.
  2. Identify True Risk.
  3. Proactively Mitigate Threats.

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