CVE-2016-4553

client_side.cc in Squid before 3.5.18 and 4.x before 4.0.10 does not properly ignore the Host header when absolute-URI is provided, which allows remote attackers to conduct cache-poisoning attacks via an HTTP request.

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-2016-4553 is rated High Risk (74.1/100): CVSS High severity, with high exploitation likelihood (EPSS 82.84%, 99th percentile). EPSS ranks this CVE among the most likely to be exploited in the near term. EPSS rose +43.31% over the last day, indicating growing attacker interest. 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-2016-4553

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 2025-12-28 39.53% 82.84% +43.31%
2 2025-12-27 82.84% 39.53% -43.31%
3 2025-10-28 — 82.84% —

Full EPSS history (21 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2016-4553

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
8.6 3.0 HIGH
CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:H/A:N 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:C)
Breaking this can reach past the original component and bite other resources—bigger blast radius.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:N)
Service keeps running; no real outage angle.
 3.9 4.0 [email protected]
5.0 2.0 MEDIUM
AV:N/AC:L/Au:N/C:N/I:P/A:N 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:P)
Partial integrity impact.
Availability impact (A:N)
No availability impact.
 10.0 2.9 [email protected]

Weakness enumeration for CVE-2016-4553

OS Trackers for CVE-2016-4553

vendor priority summary link
debian unimportant CVE-2016-4553 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-2016-4553
gentoo normal CVE-2016-4553: 1 GLSA(s) (201607-01), 1 atom(s) (net-proxy/squid); latest impact normal. https://bugs.gentoo.org/buglist.cgi?quicksearch=CVE-2016-4553
redhat medium — https://access.redhat.com/security/cve/CVE-2016-4553
suse medium CVE-2016-4553 severity moderate: SUSE including 246 source package names (amazon/suse-sles-15-sp1-chost-byos-v20210304-hvm-ssd-x86_64, amazon/suse-sles-15-sp1-chost-byos-v20220127-hvm-ssd-x86_64, …), 274 product×package rows across 40 product lines (HPE Helion OpenStack 8, SUSE Liberty Linux 7, … (40 product lines)): Known Affected 231, Known Not Affected 22, Fixed 21. https://www.suse.com/security/cve/CVE-2016-4553/
ubuntu medium CVE-2016-4553 medium priority: Ubuntu including 1 source packages (squid3), 5 status rows across 5 suites (precise, trusty, upstream, wily, xenial): released 4, not-affected 1. https://ubuntu.com/security/CVE-2016-4553

Affected software / configurations for CVE-2016-4553

Vendor Product Version Raw CPE
canonical ubuntu_linux 12.04 cpe:2.3:o:canonical:ubuntu_linux:12.04:*:*:*:lts:*:*:*
canonical ubuntu_linux 14.04 cpe:2.3:o:canonical:ubuntu_linux:14.04:*:*:*:lts:*:*:*
canonical ubuntu_linux 15.10 cpe:2.3:o:canonical:ubuntu_linux:15.10:*:*:*:*:*:*:*
canonical ubuntu_linux 16.04 cpe:2.3:o:canonical:ubuntu_linux:16.04:*:*:*:lts:*:*:*
squid-cache squid <= 3.5.17 cpe:2.3:a:squid-cache:squid:*:*:*:*:*:*:*:*
squid-cache squid 4.0.1 cpe:2.3:a:squid-cache:squid:4.0.1:*:*:*:*:*:*:*
squid-cache squid 4.0.2 cpe:2.3:a:squid-cache:squid:4.0.2:*:*:*:*:*:*:*
squid-cache squid 4.0.3 cpe:2.3:a:squid-cache:squid:4.0.3:*:*:*:*:*:*:*
squid-cache squid 4.0.4 cpe:2.3:a:squid-cache:squid:4.0.4:*:*:*:*:*:*:*
squid-cache squid 4.0.5 cpe:2.3:a:squid-cache:squid:4.0.5:*:*:*:*:*:*:*
squid-cache squid 4.0.6 cpe:2.3:a:squid-cache:squid:4.0.6:*:*:*:*:*:*:*
squid-cache squid 4.0.7 cpe:2.3:a:squid-cache:squid:4.0.7:*:*:*:*:*:*:*
squid-cache squid 4.0.8 cpe:2.3:a:squid-cache:squid:4.0.8:*:*:*:*:*:*:*
squid-cache squid 4.0.9 cpe:2.3:a:squid-cache:squid:4.0.9:*:*:*:*:*:*:*
oracle linux 7 cpe:2.3:o:oracle:linux:7:*:*:*:*:*:*:*

References for CVE-2016-4553

URL Tags
http://bugs.squid-cache.org/show_bug.cgi?id=4501 Vendor Advisory
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.oracle.com/technetwork/topics/security/linuxbulletinapr2016-2952096.html Third Party Advisory
http://www.securitytracker.com/id/1035768 Third Party Advisory
http://www.squid-cache.org/Advisories/SQUID-2016_7.txt Vendor Advisory
http://www.squid-cache.org/Versions/v3/3.5/changesets/squid-3.5-14039.patch
http://www.ubuntu.com/usn/USN-2995-1 Third Party Advisory
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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