{"cve":"CVE-2019-12520","nvd":{"published":"2020-04-15T20:15:13.520","modified":"2026-06-17T02:14:48.620","status":"Modified","description":"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.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N","score":7.5},"cwes":["CWE-20"],"references":["http://www.squid-cache.org/Versions/v4/","http://www.squid-cache.org/Versions/v4/changesets/","https://github.com/squid-cache/squid/commits/v4","https://gitlab.com/jeriko.one/security/-/blob/master/squid/CVEs/CVE-2019-12520.txt","https://lists.debian.org/debian-lts-announce/2020/07/msg00009.html"],"products":["canonical:ubuntu_linux","debian:debian_linux","squid-cache:squid"],"source":"nvd","synced_at":"2026-10-19T21:04:18.695612450+00:00"},"epss":{"cve":"CVE-2019-12520","score":0.03924,"percentile":0.90353,"date":"2026-11-01"},"kev":null,"osv":[],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}