Gentoo Linux Security Advisory GLSA 200804-15 – Tavis Ormandy of the Google Security Team discovered that libpng does not handle zero-length unknown chunks in PNG files correctly, which might lead to memory corruption in applications that call png_set_read_user_chunk_fn() or png_set_keep_unknown_chunks(). Versions less than 1.2.26-r1 are affected.
You can download this advisory from the following link: https://packetstormsecurity.com/files/download/65527/glsa-200804-15.txt
Source: https://packetstormsecurity.com/files/65527/Gentoo-Linux-Security-Advisory-200804-15.html