An issue was discovered in Squid before 4.9. URN response handling in Squid suffers from a heap-based buffer overflow. When receiving data from a remote server in response to an URN request, Squid fails to ensure that the response can fit within the buffer. This leads to attacker controlled data overflowing in the heap.
https://www.debian.org/security/2020/dsa-4682
https://usn.ubuntu.com/4213-1/
https://security.gentoo.org/glsa/202003-34
https://lists.debian.org/debian-lts-announce/2020/07/msg00009.html
https://lists.debian.org/debian-lts-announce/2019/12/msg00011.html