A heap out-of-bounds write vulnerability exists in the BlobStream component of ImageMagick 7 (MagickCore) due to improper handling of forward seeks beyond the current buffer extent. This allows an attacker to write controlled bytes at an attacker-chosen offset beyond the allocated memory, leading to memory corruption and potential remote code execution. The flaw affects versions prior to 14.8.2 and has been confirmed on macOS arm64 and is architecture-agnostic on LP64 systems. The vulnerability arises because the WriteBlob function grows the buffer insufficiently when the offset is far beyond the current extent, causing a deterministic heap overflow. The vulnerability has a CVSS score of 3.8 with low severity in the Magick.NET Q16 x64 context, but the underlying ImageMagick flaw is rated 9.8 in CVSS v3.1. A fix is available in version 14.8.2.