Input validation error in Squid - CVE-2021-28651
Published: May 10, 2021 / Updated: May 1, 2026
Vulnerability identifier: #VU53017
CSH Severity: Medium
CVSS v4.0: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:U/U:Green
CVE-ID: CVE-2021-28651
CWE-ID: CWE-20
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vendor: Squid-cache.org
Affected software:
Squid
Squid
Detailed vulnerability description
The vulnerability allows a remote attacker to perform a denial of service (DoS) attack.
The vulnerability exists due to insufficient input validation when resolving "urn:" resource identifiers. A remote attacker can trick a user behind the proxy server to click on a specially crafted "urn:" link that leads to a server under attacker's control and force Squid to consume arbitrarily large amounts of memory on the server.
How to mitigate CVE-2021-28651
Install updates from vendor's website.