Out-of-bounds write in Squid - CVE-2019-12521

Vulnerability identifier: #VU27667

CSH Severity: Medium

CVSS v4: 8.7 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N]

CVE-ID: CVE-2019-12521

CWE-ID: CWE-787

Exploitation vector: Remote access

Exploit availability: No public exploit available

The vulnerability allows a remote attacker to perform a denial of service (DoS) attack.

The vulnerability exists due to a boundary error when processing untrusted input. When Squid is parsing ESI, it keeps the ESI elements in ESIContext. ESIContext contains a buffer for holding a stack of ESIElements. When a new ESIElement is parsed, it is added via addStackElement. addStackElement has a check for the number of elements in this buffer, but it's off by 1, leading to a Heap Overflow of 1 element. The overflow is within the same structure so it can't affect adjacent memory blocks, and thus just leads to a crash while processing.

Squid
Gentoo Linux
Amazon Linux AMI
Anolis OS
Red Hat Enterprise Linux for ARM 64
Red Hat Enterprise Linux for x86_64
Red Hat Enterprise Linux for IBM z Systems
Red Hat Enterprise Linux for Power, little endian
Opensuse
openEuler
squid (Debian package)
squid (Alpine package)
squid3 (Ubuntu package)
squid (Ubuntu package)
libecap
libecap-devel
squid
squid-debuginfo
squid-debugsource

Install updates from vendor's website.

Squid - addressed in versions 4.8, 5.0.2
squid (Debian package) - update to 4.6-1+deb10u2
squid3 (Ubuntu package) - addressed in versions 3.5.12-1ubuntu7.11, 3.5.27-1ubuntu1.6
squid (Ubuntu package) - addressed in versions 4.8-1ubuntu2.3, 4.10-1ubuntu1.1
libecap - update to 1.0.1-2
libecap-devel - update to 1.0.1-2
squid - update to 4.9-11
squid-debuginfo - update to 4.9-11
squid-debugsource - update to 4.9-11
squid - update to 4.11-4

• http://www.openwall.com/lists/oss-security/2020/04/23/1
• https://gitlab.com/jeriko.one/security/-/blob/master/squid/CVEs/CVE-2019-12521.txt
• https://www.debian.org/security/2020/dsa-4682
• http://www.squid-cache.org/Advisories/SQUID-2019_12.txt

• Multiple vulnerabilities in Squid Proxy Cache
• Debian update for squid
• OpenSUSE Linux update for squid
• Gentoo update for Squid
• Ubuntu update for Squid
• Amazon Linux AMI update for squid
• Red Hat Enterprise Linux 8 update for the squid:4 module
• Out-of-bounds write in squid (Alpine package)
• openEuler 20.03 LTS SP1 update for squid
• Anolis OS update for squid:4 (Anolis OS 8.4) module