CVE-2018-20847 in OpenJPEG
Summary
by MITRE
An improper computation of p_tx0, p_tx1, p_ty0 and p_ty1 in the function opj_get_encoding_parameters in openjp2/pi.c in OpenJPEG through 2.3.0 can lead to an integer overflow.
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Analysis
by VulDB Data Team • 10/08/2023
The vulnerability identified as CVE-2018-20847 represents a critical integer overflow flaw within the OpenJPEG library version 2.3.0 and earlier. This issue resides in the opj_get_encoding_parameters function located in the openjp2/pi.c source file, where the improper computation of four variables p_tx0, p_tx1, p_ty0, and p_ty1 creates a pathway for malicious exploitation. The flaw manifests when the library processes JPEG 2000 encoded data, particularly during the encoding parameter calculation phase where these variables are intended to represent tile coordinates and dimensions.
The technical implementation of this vulnerability stems from inadequate input validation and arithmetic handling within the encoding parameter computation routine. When processing malformed or specially crafted JPEG 2000 streams, the function fails to properly validate the boundaries and dimensions of tiles, leading to scenarios where arithmetic operations on these variables exceed their maximum representable values. This integer overflow condition occurs because the computation does not account for potential overflow during the calculation of tile coordinates, particularly when dealing with large image dimensions or complex compression parameters.
The operational impact of this vulnerability extends beyond simple denial of service scenarios, as it creates potential exploitation vectors for remote code execution attacks. An attacker who can control the input to the OpenJPEG library through a JPEG 2000 file could potentially manipulate the tile coordinate calculations to cause memory corruption. The overflow affects the p_tx0, p_tx1, p_ty0, and p_ty1 variables which are fundamental to determining how image data is segmented into tiles during the compression process. When these values overflow, they can corrupt adjacent memory locations, potentially allowing for arbitrary code execution or system instability.
This vulnerability aligns with CWE-190, Integer Overflow or Wraparound, which specifically addresses issues where computations involving integers exceed their maximum representable values. The flaw also maps to ATT&CK technique T1203, Exploitation for Client Execution, as it represents a classic client-side exploitation vector where a malicious file can trigger the vulnerability when processed by an application using the vulnerable OpenJPEG library. The attack surface is particularly broad given that OpenJPEG is widely used across numerous applications and systems for JPEG 2000 image processing, making this vulnerability particularly dangerous in environments where users might encounter maliciously crafted image files.
Mitigation strategies for CVE-2018-20847 require immediate patching of affected OpenJPEG installations to version 2.3.1 or later, where the integer overflow conditions have been addressed through proper input validation and arithmetic boundary checks. Organizations should also implement network-based filtering to block suspicious JPEG 2000 files and deploy application whitelisting measures to restrict execution of vulnerable software components. Additionally, security monitoring should be enhanced to detect unusual memory access patterns or process behaviors that might indicate exploitation attempts. The fix implemented in the patched versions includes comprehensive validation of tile coordinate calculations and proper handling of boundary conditions to prevent arithmetic overflow scenarios from occurring during normal operation.