high
7.5
CWE
20
Advisory Published
Updated

CVE-2019-12520: Input Validation

First published: Wed Apr 15 2020(Updated: )

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.

Credit: cve@mitre.org cve@mitre.org

Affected SoftwareAffected VersionHow to fix
Squid-Cache Squid<=4.7
Canonical Ubuntu Linux=16.04
Canonical Ubuntu Linux=18.04
Debian Debian Linux=9.0
Debian Debian Linux=10.0
ubuntu/squid<4.8
4.8
ubuntu/squid3<3.5.27-1ubuntu1.7
3.5.27-1ubuntu1.7
debian/squid
4.6-1+deb10u7
4.6-1+deb10u10
4.13-10+deb11u2
4.13-10+deb11u3
5.7-2
5.7-2+deb12u1
6.6-1
6.9-1

Remedy

https://github.com/squid-cache/squid/commits/v4

Remedy

http://www.squid-cache.org/Versions/v4/changesets/SQUID-2019_4.patch

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Reference Links

Parent vulnerabilities

(Appears in the following advisories)

Frequently Asked Questions

  • What is CVE-2019-12520?

    CVE-2019-12520 is an issue discovered in Squid through version 4.7 and 5 that allows an attacker to bypass access restrictions.

  • How does CVE-2019-12520 work?

    CVE-2019-12520 works by making a MD5 hash of the absolute URL of a request in Squid and serves the request if it is found in the cache.

  • Which software versions are affected by CVE-2019-12520?

    CVE-2019-12520 affects Squid versions 4.6-1+deb10u7, 4.6-1+deb10u8, 4.13-10+deb11u2, 5.7-2, and 6.3-1, as well as Ubuntu Linux 16.04, Ubuntu Linux 18.04, and Debian Linux 9.0 and 10.0.

  • What is the severity of CVE-2019-12520?

    CVE-2019-12520 has a severity rating of 7.5 (high).

  • How can I fix CVE-2019-12520?

    To fix CVE-2019-12520, update Squid to version 4.8 or later, or apply the relevant patches provided by Squid.

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