ImageSharp provides 2‑D graphics support and includes a TIFF decoder. Between versions 3.0.0 and 4.1.1 the library allows a strip of a TIFF image to be decoded using CCITT Group 3 or Modified Huffman compression. Attackers can craft a TIFF file that expands run‑length entries so that the BitWriterUtils.WriteBits routine writes an unchecked number of bits, overflowing the strip buffer and corrupting adjacent heap memory. The corruption can terminate the process and could also lead to denial of service.

The vulnerability affects SixLabors ImageSharp versions 3.0.0 through 4.1.1. Updated releases starting with 4.1.1 contain a patch that validates run lengths before writing bits.

The CVSS score of 7.5 signals high severity, but no EPSS data are available and the vulnerability is not listed in CISA KEV. The likely attack vector is a file-based exploit: an attacker supplies a malicious TIFF image to an application that uses the affected ImageSharp library. The vulnerability can be triggered when the application attempts to decode the image, potentially causing a crash or, if memory corruption is exploited, denial of service. The lack of empirical exploitation data combined with the high CVSS suggests that this issue poses a real risk to applications that process untrusted TIFF files.