#VU53017 Input validation error in Squid - CVE-2021-28651

Vulnerability identifier: #VU53017

Vulnerability risk: Medium

CVSSv4.0: 4.6 [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: Network

Exploit availability: No

Vulnerable software:
Squid
Server applications / IDS/IPS systems, Firewalls and proxy servers

Vendor: Squid-cache.org

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. 

Mitigation
Install updates from vendor's website.

Vulnerable software versions

Squid: 2.0.release - 2.0_patch2, 2.1.release - 2.1.pre4, 2.2.stable1 - 2.2.pre2, 2.3.stable1 - 2.3, 2.4.stable1 - 2.4_9, 2.5.stable1 - 2.5.9, 2.6.stable1 - 2.6, 2.7.stable1 - 2.7, 3.0.stable1 - 3.5.28, 4.0 - 4.14, 5.0 - 5.0.5

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External links
https://github.com/squid-cache/squid/security/advisories/GHSA-ch36-9jhx-phm4/

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Q & A

Can this vulnerability be exploited remotely?

Yes. This vulnerability can be exploited by a remote non-authenticated attacker via the Internet.

Is there known malware, which exploits this vulnerability?

No. We are not aware of malware exploiting this vulnerability.