ImageSharp: BigTIFF IFD count can keep a decoder thread in a non-progressing loop

[ Why it matters ]Priority signals

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

[ Description ]Official description

ImageSharp is a 2D graphics library. From 2.0.0 until 4.1.2, ExifReader.ReadValues64 trusts the 64-bit BigTIFF IFD entry count and iterates once per declared entry. When fewer than 20 bytes remain, ExifReader.ReadValue64 returns without advancing the stream or terminating the outer loop, so a small malformed BigTIFF can keep one decoder thread executing for an attacker-controlled duration. This report does not claim worker-pool exhaustion. 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 >= 2.0.0, <= 4.1.1)

[ Packages ]Affected open-source packages

• SixLabors.ImageSharp nugetAffected >= 2.0.0, <= 4.1.1 · fixed in 4.1.2 · GHSA-wmxv-xphr-5c9g

[ References ]References

• github.com/SixLabors/ImageSharp/commit/92b12d72550ebb6be5b1e22e559c361fd863a6ec
• github.com/SixLabors/ImageSharp/pull/3187
• github.com/SixLabors/ImageSharp/releases/tag/v4.1.2
• github.com/SixLabors/ImageSharp/security/advisories/GHSA-wmxv-xphr-5c9g