ImageSharp: TIFF CCITT T6 encoder writes beyond an undersized output buffer

[ Why it matters ]Priority signals

• Public proof-of-concept exploit exists (CISA SSVC)

[ Description ]Official description

ImageSharp is a 2D graphics library. From 2.1.0 until 4.1.2, the TIFF CCITT Group 4 encoder allocates Width times rowsPerStrip bytes even though T6BitCompressor.CompressStrip can emit encoded row data and two 12-bit end-of-facsimile-block codes beyond that capacity. TiffCcittCompressor.WriteCode performs unchecked writes, and a decode-and-re-encode flow can inherit TiffCompression.CcittGroup4Fax and one-bit metadata from attacker-supplied input. The resulting out-of-bounds writes can corrupt memory and terminate the process. This issue is fixed in version 4.1.2.

[ Fixes ]Fixes and patches

• SixLabors.ImageSharp 4.1.2Fixed version · GitHub Advisories · nuget package SixLabors.ImageSharp: upgrade to 4.1.2 or later (affected >= 2.1.0, <= 4.1.1)

[ Packages ]Affected open-source packages

• SixLabors.ImageSharp nugetAffected >= 2.1.0, <= 4.1.1 · fixed in 4.1.2 · GHSA-jjfr-hcj7-qf5w

[ References ]References

• github.com/SixLabors/ImageSharp/commit/a9498c6db3642ef92c712ebc81e706914ac16a95
• github.com/SixLabors/ImageSharp/pull/3187
• github.com/SixLabors/ImageSharp/releases/tag/v4.1.2
• github.com/SixLabors/ImageSharp/security/advisories/GHSA-jjfr-hcj7-qf5w