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The CVE-2021-28053 vulnerability occurs in the bilateral filter function of OpenCV, specifically within the BilateralBlurImage method. When this method is invoked, it calls AcquireBilateralTLS to allocate a set of double buffers for thread-local storage (TLS) to handle multi-threaded image processing efficiently. During allocation, the last element in the buffer set is not properly initialized, leaving it as an uninitialized pointer. This initialization flaw happens when memory allocation for the buffers is attempted. If the allocation fails due to insufficient memory or system constraints, the function DestroyBilateralTLS is triggered to release the allocated resources. In DestroyBilateralTLS, the code iterates through the buffer set to free each pointer. However, since the last pointer is uninitialized, it attempts to release an invalid memory address, leading to a use-after-free condition. This can corrupt memory management structures and cause undefined behavior. The issue is exploitable when processing maliciously crafted images that induce allocation failures, often through large or specially formatted inputs. Attackers can leverage this to crash the application (denial of service) or potentially execute arbitrary code by manipulating memory layouts. The vulnerability affects OpenCV versions prior to 4.5.2, where the bilateral filter is commonly used for image smoothing. The use-after-free can be triggered remotely in services that process user-uploaded images, making it critical for systems using OpenCV in web applications or cloud services. The flaw stems from improper error handling in TLS management, where uninitialized pointers are not validated before release. This allows an attacker to control or predict memory addresses for exploitation. The vulnerability was patched by ensuring proper initialization of all buffer elements in AcquireBilateralTLS and adding checks in DestroyBilateralTLS to avoid releasing invalid pointers.
Platform: OpenCV
Version: Before 4.5.2
Vulnerability: Use After Free
Severity: Critical
Date: 2021-03-05
Prediction: Patched 2021-03-05
What Undercode Say:
Analytics:
- Check version: `pkg-config –modversion opencv`
– Vulnerable code: `bilateralFilter(src, dst, d, sigmaColor, sigmaSpace)`
– Trigger allocation failure: `ulimit -v 1024; ./opencv_program`
– Debug with GDB: `gdb –args ./program image.jpg`
– Patch verification: `git log –oneline | grep bilateral`
– Exploit snippet: `cv2.bilateralFilter(img, 9, 75, 75)`
– Memory check: `valgrind ./opencv_app`
– Build from source: `cmake -D CMAKE_BUILD_TYPE=Release ..`
– Test for vulnerability: `python -c “import cv2; cv2.bilateralFilter(…)”`
How Exploit:
Craft malicious image to trigger memory allocation failure in bilateral filter, causing use-after-free for code execution via heap manipulation.
Protection from this CVE
Update to OpenCV 4.5.2 or later; validate image inputs; use memory sanitizers.
Impact:
Remote code execution or denial of service.
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Sources:
Reported By: github.com
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