An issue was discovered in Squid through 4.7 and 5. When receiving a request, Squid checks its cache to see if it can serve up a response. It does this by making a MD5 hash of the absolute URL of the request. If found, it servers the request. The absolute URL can include the decoded UserInfo (username and password) for certain protocols. This decoded info is prepended to the domain. This allows an attacker to provide a username that has special characters to delimit the domain, and treat the rest of the URL as a path or query string. An attacker could first make a request to their domain using an encoded username, then when a request for the target domain comes in that decodes to the exact URL, it will serve the attacker's HTML instead of the real HTML. On Squid servers that also act as reverse proxies, this allows an attacker to gain access to features that only reverse proxies can use, such as ESI.

Affected: Ubuntu:16.04:LTS: squid3, Ubuntu:18.04:LTS: squid3

Jeriko One discovered that Squid incorrectly handled caching certain requests. A remote attacker could possibly use this issue to perform cache-injection attacks or gain access to reverse proxy features such as ESI. (CVE-2019-12520)

Jeriko One and Kristoffer Danielsson discovered that Squid incorrectly handled certain URN requests. A remote attacker could possibly use this issue to bypass access checks. (CVE-2019-12523)

Jeriko One discovered that Squid incorrectly handled URL decoding. A remote attacker could possibly use this issue to bypass certain rule checks. (CVE-2019-12524)

Jeriko One and Kristoffer Danielsson discovered that Squid incorrectly handled input validation. A remote attacker could use this issue to cause Squid to crash, resulting in a denial of service. (CVE-2019-18676)