CVE-2026-106117: ImageSharp: CCITT fax decompression (T4/Modified Huffman): unbounded WriteBits overflows strip buffer — heap OOB write in SixLabors.ImageSharp

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2026-10-06 · updated 2026-10-27
Weakness: CWE-787

Description

ImageSharp is a 2D graphics library. From 3.0.0 until 4.1.1, decoding a strip TIFF using CCITT Group 3 or Modified Huffman compression can pass attacker-expanded runs to BitWriterUtils.WriteBits without first checking the current row width. T4TiffCompression.WritePixelRun can accumulate oversized makeup-code runs, and ModifiedHuffmanTiffCompression.Decompress validates the width only after writing. The unchecked writes can overflow the strip buffer, corrupt heap memory, and terminate the process. This strip-path vulnerability is distinct from the tiled decompressor-width mismatch. This issue is fixed in version 4.1.1.

Affected products

SixLabors ImageSharp: from 3.0.0 before 3.2.0; from 4.0.0 before 4.1.1 — fixed in 3.2.0, 4.1.1
SixLabors ImageSharp: from 3.0.0, < 4.1.1

How to fix

Upgrade to a fixed version: SixLabors ImageSharp 3.2.0, 4.1.1. Check the vendor advisory for mitigations.

References

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