SB2020082730 - Ubuntu update for squid3

Description

This security bulletin contains information about 4 secuirty vulnerabilities.

1) Input validation error (CVE-ID: CVE-2019-12520)

The vulnerability allows a remote attacker to perform cache poisoning.

The vulnerability exists due to insufficient validation of user-supplied input within ESI. 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.

2) Input validation error (CVE-ID: CVE-2019-12523)

The vulnerability allows a remote attacker to bypass certain security restrictions.

The vulnerability exists due to insufficient validation of user-supplied input when processing URIs. A remote authenticated attacker can add certain characters to the URI, bypass implemented security restrictions and access restricted websites.

3) Missing Authentication for Critical Function (CVE-ID: CVE-2019-12524)

The vulnerability allows a remote attacker to bypass certain security restrictions.

When handling requests from users, Squid checks its rules to see if the request should be denied. Squid by default comes with rules to block access to the Cache Manager, which serves detailed server information meant for the maintainer. This rule is implemented via url_regex. The handler for url_regex rules URL decodes an incoming request. This allows an attacker to encode their URL to bypass the url_regex check, and gain access to the blocked resource.

4) Input validation error (CVE-ID: CVE-2019-18676)

The vulnerability allows a remote attacker to perform a denial of service attack.

The vulnerability exists due to insufficient validation of user-supplied input when processing URIs. A remote attacker can create a specially crafted link, trick the victim into visiting it, trigger buffer overflow and crash the Squid process.

Remediation

Install update from vendor's website.

References

• https://ubuntu.com/security/notices/USN-4446-2