CVE-2019-12520

What it is

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.

At a glance

Exploitability

Can be exploited over the network without logging in. High risk of data exposure.

Exploit odds

3.9% chance of exploitation in the next 30 days (EPSS).

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2020-04-15 20:15 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-06-17 02:14 UTC Last updatedMost recent change to the record

Why it ranks here

• Exploited in the wild: no, CISA does not list it.
• Exploit odds: 3.9% in the next 30 days (EPSS).
• Severity: 7.5 HIGH (CVSS).
• Fix: a patch or advisory is linked.

Details

Published

2020-04-15 20:15 UTC

Last modified

2026-06-17 02:14 UTC

Exploit probability

3.9% · EPSS, next 30 days

Weakness

CWE-20 · Improper input validation

Record status

Modified

Affected

• squid-cache Squid ≤ 4.7
• Canonical Ubuntu Linux 16.04
• Canonical Ubuntu Linux 18.04
• Debian Linux 9.0
• Debian Linux 10.0

Attack profile CVSS 3.1 · 7.5

Attack vector

Network

Complexity

Low

Privileges needed

None

User interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

None

Availability

None

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2019-12520.md and follow it. Check whether this project is affected by CVE-2019-12520. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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