CVE-2016-4556

Double free vulnerability in Esi.cc in Squid 3.x before 3.5.18 and 4.x before 4.0.10 allows remote servers to cause a denial of service (crash) via a crafted Edge Side Includes (ESI) response.

Published: 2016-05-10 Last update: 2026-05-06 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2016-4556 is rated Moderate Risk (59.3/100): CVSS High severity, with high exploitation likelihood (EPSS 56.86%, 98th percentile). EPSS ranks this CVE among the most likely to be exploited in the near term. High exploitation likelihood—assess exposure and prioritize remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2016-4556

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-03-04 67.25% 56.86% -10.39%
2 2026-03-01 56.86% 67.25% +10.39%
3 2026-02-04 — 56.86% —

Full EPSS history (49 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2016-4556

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
7.5 3.0 HIGH
CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 3.9 3.6 [email protected]
5.0 2.0 MEDIUM
AV:N/AC:L/Au:N/C:N/I:N/A:P Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:L)
Exploitation conditions are straightforward and predictable.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:N)
No confidentiality impact.
Integrity impact (I:N)
No integrity impact.
Availability impact (A:P)
Partial availability impact.
 10.0 2.9 [email protected]

Weakness enumeration for CVE-2016-4556

OS Trackers for CVE-2016-4556

vendor priority summary link
debian unimportant CVE-2016-4556 unimportant priority: Debian including 1 source packages (squid), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5. https://security-tracker.debian.org/tracker/CVE-2016-4556
gentoo normal CVE-2016-4556: 1 GLSA(s) (201607-01), 1 atom(s) (net-proxy/squid); latest impact normal. https://bugs.gentoo.org/buglist.cgi?quicksearch=CVE-2016-4556
redhat medium — https://access.redhat.com/security/cve/CVE-2016-4556
suse medium CVE-2016-4556 severity moderate: SUSE including 14 source package names (squid, squid-3.3.14-20.2, …), 42 product×package rows across 38 product lines (HPE Helion OpenStack 8, SUSE Liberty Linux 7, … (38 product lines)): Known Not Affected 22, Fixed 20. https://www.suse.com/security/cve/CVE-2016-4556/
ubuntu medium CVE-2016-4556 medium priority: Ubuntu including 1 source packages (squid3), 5 status rows across 5 suites (precise, trusty, upstream, wily, xenial): released 4, needs-triage 1. https://ubuntu.com/security/CVE-2016-4556

NVD evaluator notes for CVE-2016-4556

Comment: <a href="http://cwe.mitre.org/data/definitions/415.html">CWE-415: Double Free</a>

Affected software / configurations for CVE-2016-4556

Vendor Product Version Raw CPE
squid-cache squid 3.0 cpe:2.3:a:squid-cache:squid:3.0:*:*:*:*:*:*:*
squid-cache squid 3.1 cpe:2.3:a:squid-cache:squid:3.1:*:*:*:*:*:*:*
squid-cache squid 3.1.0.1 cpe:2.3:a:squid-cache:squid:3.1.0.1:*:*:*:*:*:*:*
squid-cache squid 3.1.0.2 cpe:2.3:a:squid-cache:squid:3.1.0.2:*:*:*:*:*:*:*
squid-cache squid 3.1.0.3 cpe:2.3:a:squid-cache:squid:3.1.0.3:*:*:*:*:*:*:*
squid-cache squid 3.1.0.4 cpe:2.3:a:squid-cache:squid:3.1.0.4:*:*:*:*:*:*:*
squid-cache squid 3.1.0.5 cpe:2.3:a:squid-cache:squid:3.1.0.5:*:*:*:*:*:*:*
squid-cache squid 3.1.0.6 cpe:2.3:a:squid-cache:squid:3.1.0.6:*:*:*:*:*:*:*
squid-cache squid 3.1.0.7 cpe:2.3:a:squid-cache:squid:3.1.0.7:*:*:*:*:*:*:*
squid-cache squid 3.1.0.8 cpe:2.3:a:squid-cache:squid:3.1.0.8:*:*:*:*:*:*:*
squid-cache squid 3.1.0.9 cpe:2.3:a:squid-cache:squid:3.1.0.9:*:*:*:*:*:*:*
squid-cache squid 3.1.0.10 cpe:2.3:a:squid-cache:squid:3.1.0.10:*:*:*:*:*:*:*
squid-cache squid 3.1.0.11 cpe:2.3:a:squid-cache:squid:3.1.0.11:*:*:*:*:*:*:*
squid-cache squid 3.1.0.12 cpe:2.3:a:squid-cache:squid:3.1.0.12:*:*:*:*:*:*:*
squid-cache squid 3.1.0.13 cpe:2.3:a:squid-cache:squid:3.1.0.13:*:*:*:*:*:*:*
squid-cache squid 3.1.0.14 cpe:2.3:a:squid-cache:squid:3.1.0.14:*:*:*:*:*:*:*
squid-cache squid 3.1.0.15 cpe:2.3:a:squid-cache:squid:3.1.0.15:*:*:*:*:*:*:*
squid-cache squid 3.1.0.16 cpe:2.3:a:squid-cache:squid:3.1.0.16:*:*:*:*:*:*:*
squid-cache squid 3.1.0.17 cpe:2.3:a:squid-cache:squid:3.1.0.17:*:*:*:*:*:*:*
squid-cache squid 3.1.0.18 cpe:2.3:a:squid-cache:squid:3.1.0.18:*:*:*:*:*:*:*
squid-cache squid 3.1.1 cpe:2.3:a:squid-cache:squid:3.1.1:*:*:*:*:*:*:*
squid-cache squid 3.1.2 cpe:2.3:a:squid-cache:squid:3.1.2:*:*:*:*:*:*:*
squid-cache squid 3.1.3 cpe:2.3:a:squid-cache:squid:3.1.3:*:*:*:*:*:*:*
squid-cache squid 3.1.4 cpe:2.3:a:squid-cache:squid:3.1.4:*:*:*:*:*:*:*
squid-cache squid 3.1.5 cpe:2.3:a:squid-cache:squid:3.1.5:*:*:*:*:*:*:*
squid-cache squid 3.1.5.1 cpe:2.3:a:squid-cache:squid:3.1.5.1:*:*:*:*:*:*:*
squid-cache squid 3.1.6 cpe:2.3:a:squid-cache:squid:3.1.6:*:*:*:*:*:*:*
squid-cache squid 3.1.7 cpe:2.3:a:squid-cache:squid:3.1.7:*:*:*:*:*:*:*
squid-cache squid 3.1.8 cpe:2.3:a:squid-cache:squid:3.1.8:*:*:*:*:*:*:*
squid-cache squid 3.1.9 cpe:2.3:a:squid-cache:squid:3.1.9:*:*:*:*:*:*:*
squid-cache squid 3.1.10 cpe:2.3:a:squid-cache:squid:3.1.10:*:*:*:*:*:*:*
squid-cache squid 3.1.11 cpe:2.3:a:squid-cache:squid:3.1.11:*:*:*:*:*:*:*
squid-cache squid 3.1.12 cpe:2.3:a:squid-cache:squid:3.1.12:*:*:*:*:*:*:*
squid-cache squid 3.1.12.1 cpe:2.3:a:squid-cache:squid:3.1.12.1:*:*:*:*:*:*:*
squid-cache squid 3.1.12.2 cpe:2.3:a:squid-cache:squid:3.1.12.2:*:*:*:*:*:*:*
squid-cache squid 3.1.12.3 cpe:2.3:a:squid-cache:squid:3.1.12.3:*:*:*:*:*:*:*
squid-cache squid 3.1.13 cpe:2.3:a:squid-cache:squid:3.1.13:*:*:*:*:*:*:*
squid-cache squid 3.1.14 cpe:2.3:a:squid-cache:squid:3.1.14:*:*:*:*:*:*:*
squid-cache squid 3.1.15 cpe:2.3:a:squid-cache:squid:3.1.15:*:*:*:*:*:*:*
squid-cache squid 3.1.16 cpe:2.3:a:squid-cache:squid:3.1.16:*:*:*:*:*:*:*
squid-cache squid 3.1.17 cpe:2.3:a:squid-cache:squid:3.1.17:*:*:*:*:*:*:*
squid-cache squid 3.1.18 cpe:2.3:a:squid-cache:squid:3.1.18:*:*:*:*:*:*:*
squid-cache squid 3.1.19 cpe:2.3:a:squid-cache:squid:3.1.19:*:*:*:*:*:*:*
squid-cache squid 3.1.20 cpe:2.3:a:squid-cache:squid:3.1.20:*:*:*:*:*:*:*
squid-cache squid 3.1.21 cpe:2.3:a:squid-cache:squid:3.1.21:*:*:*:*:*:*:*
squid-cache squid 3.1.22 cpe:2.3:a:squid-cache:squid:3.1.22:*:*:*:*:*:*:*
squid-cache squid 3.2.0.1 cpe:2.3:a:squid-cache:squid:3.2.0.1:*:*:*:*:*:*:*
squid-cache squid 3.2.0.2 cpe:2.3:a:squid-cache:squid:3.2.0.2:*:*:*:*:*:*:*
squid-cache squid 3.2.0.3 cpe:2.3:a:squid-cache:squid:3.2.0.3:*:*:*:*:*:*:*
squid-cache squid 3.2.0.4 cpe:2.3:a:squid-cache:squid:3.2.0.4:*:*:*:*:*:*:*
squid-cache squid 3.2.0.5 cpe:2.3:a:squid-cache:squid:3.2.0.5:*:*:*:*:*:*:*
squid-cache squid 3.2.0.6 cpe:2.3:a:squid-cache:squid:3.2.0.6:*:*:*:*:*:*:*
squid-cache squid 3.2.0.7 cpe:2.3:a:squid-cache:squid:3.2.0.7:*:*:*:*:*:*:*
squid-cache squid 3.2.0.8 cpe:2.3:a:squid-cache:squid:3.2.0.8:*:*:*:*:*:*:*
squid-cache squid 3.2.0.9 cpe:2.3:a:squid-cache:squid:3.2.0.9:*:*:*:*:*:*:*
squid-cache squid 3.2.0.10 cpe:2.3:a:squid-cache:squid:3.2.0.10:*:*:*:*:*:*:*
squid-cache squid 3.2.0.11 cpe:2.3:a:squid-cache:squid:3.2.0.11:*:*:*:*:*:*:*
squid-cache squid 3.2.0.12 cpe:2.3:a:squid-cache:squid:3.2.0.12:*:*:*:*:*:*:*
squid-cache squid 3.2.0.13 cpe:2.3:a:squid-cache:squid:3.2.0.13:*:*:*:*:*:*:*
squid-cache squid 3.2.0.14 cpe:2.3:a:squid-cache:squid:3.2.0.14:*:*:*:*:*:*:*
squid-cache squid 3.2.0.15 cpe:2.3:a:squid-cache:squid:3.2.0.15:*:*:*:*:*:*:*
squid-cache squid 3.2.0.16 cpe:2.3:a:squid-cache:squid:3.2.0.16:*:*:*:*:*:*:*
squid-cache squid 3.2.0.17 cpe:2.3:a:squid-cache:squid:3.2.0.17:*:*:*:*:*:*:*
squid-cache squid 3.2.0.18 cpe:2.3:a:squid-cache:squid:3.2.0.18:*:*:*:*:*:*:*
squid-cache squid 3.2.0.19 cpe:2.3:a:squid-cache:squid:3.2.0.19:*:*:*:*:*:*:*
squid-cache squid 3.2.1 cpe:2.3:a:squid-cache:squid:3.2.1:*:*:*:*:*:*:*
squid-cache squid 3.2.2 cpe:2.3:a:squid-cache:squid:3.2.2:*:*:*:*:*:*:*
squid-cache squid 3.2.3 cpe:2.3:a:squid-cache:squid:3.2.3:*:*:*:*:*:*:*
squid-cache squid 3.2.4 cpe:2.3:a:squid-cache:squid:3.2.4:*:*:*:*:*:*:*
squid-cache squid 3.2.5 cpe:2.3:a:squid-cache:squid:3.2.5:*:*:*:*:*:*:*
squid-cache squid 3.2.6 cpe:2.3:a:squid-cache:squid:3.2.6:*:*:*:*:*:*:*
squid-cache squid 3.2.7 cpe:2.3:a:squid-cache:squid:3.2.7:*:*:*:*:*:*:*
squid-cache squid 3.2.8 cpe:2.3:a:squid-cache:squid:3.2.8:*:*:*:*:*:*:*
squid-cache squid 3.2.9 cpe:2.3:a:squid-cache:squid:3.2.9:*:*:*:*:*:*:*
squid-cache squid 3.2.10 cpe:2.3:a:squid-cache:squid:3.2.10:*:*:*:*:*:*:*
squid-cache squid 3.2.11 cpe:2.3:a:squid-cache:squid:3.2.11:*:*:*:*:*:*:*
squid-cache squid 3.2.12 cpe:2.3:a:squid-cache:squid:3.2.12:*:*:*:*:*:*:*
squid-cache squid 3.2.13 cpe:2.3:a:squid-cache:squid:3.2.13:*:*:*:*:*:*:*
squid-cache squid 3.3.0 cpe:2.3:a:squid-cache:squid:3.3.0:*:*:*:*:*:*:*
squid-cache squid 3.3.0.1 cpe:2.3:a:squid-cache:squid:3.3.0.1:*:*:*:*:*:*:*

References for CVE-2016-4556

URL Tags
http://lists.opensuse.org/opensuse-security-announce/2016-08/msg00010.html
http://lists.opensuse.org/opensuse-security-announce/2016-08/msg00040.html
http://lists.opensuse.org/opensuse-updates/2016-08/msg00069.html
http://www.debian.org/security/2016/dsa-3625
http://www.openwall.com/lists/oss-security/2016/05/06/3 Third Party Advisory
http://www.openwall.com/lists/oss-security/2016/05/06/5 Release Notes Third Party Advisory
http://www.oracle.com/technetwork/topics/security/linuxbulletinapr2016-2952096.html Third Party Advisory
http://www.securitytracker.com/id/1035770 Third Party Advisory
http://www.squid-cache.org/Advisories/SQUID-2016_9.txt Vendor Advisory
http://www.squid-cache.org/Versions/v3/3.4/changesets/SQUID-2016_9.patch
http://www.squid-cache.org/Versions/v3/3.5/changesets/SQUID-2016_9.patch Patch
http://www.ubuntu.com/usn/USN-2995-1 Third Party Advisory
https://access.redhat.com/errata/RHSA-2016:1138
https://access.redhat.com/errata/RHSA-2016:1139
https://access.redhat.com/errata/RHSA-2016:1140
https://security.gentoo.org/glsa/201607-01
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