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CVE-2016-4556

32
FAUCET Score

CVE-2016-4556 describes a double free vulnerability in Squid versions 3.x before 3.5.18 and 4.x before 4.0.10, allowing remote servers to trigger a denial of service (crash) through specially crafted Edge Side Includes (ESI) responses. This vulnerability carries a CVSSv3 score of 7.5 (HIGH), indicating it can be exploited remotely with low complexity to achieve high availability impact. While the FAUCET Risk Score is high at 97/100 and its EPSS score is above average, there is no evidence of active exploitation, publicly available exploit code (Metasploit, Nuclei, ExploitDB), or significant community discussion or media coverage.

Impacted Technologies

VendorProductVersion(s)CPE
3.0CPE matchmatch criteria
cpe:2.3:a:squid-cache:squid:3.0:*:*:*:*:*:*:*
3.1CPE matchmatch criteria
cpe:2.3:a:squid-cache:squid:3.1:*:*:*:*:*:*:*
3.1.0.1CPE matchmatch criteria
cpe:2.3:a:squid-cache:squid:3.1.0.1:*:*:*:*:*:*:*
3.1.0.2CPE matchmatch criteria
cpe:2.3:a:squid-cache:squid:3.1.0.2:*:*:*:*:*:*:*
3.1.0.3CPE matchmatch criteria
cpe:2.3:a:squid-cache:squid:3.1.0.3:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.0

7.5HIGH

CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
NONE
Integrity Impact
NONE
Availability Impact
HIGH
Exploitability Score
3.9
Impact Score
3.6
CvssVersion
3.0

Exploit Intelligence

EPSS Score
23.11%
Probability of exploitation in next 30 days
EPSS Percentile
97.5%
Percentile rank of EPSS score among Peer Group
As of 2026-07-26
Model: v2026.06.15
This CVE's current EPSS score of 0.2311 is in the 96th percentile among its peer group of 51,485 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.0 Reddit, 0.1 Bluesky, 0.1 Mastodon, and 0.4 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.1 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Patch Available

Vendor Patches (3)

redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 6Fixed in: squid-7:3.1.23-16.el6_8.4
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 6Fixed in: squid34-7:3.4.14-9.el6_8.3
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 7Fixed in: squid-7:3.3.8-26.el7_2.3
View patch

Vendor Advisories (1)

redhatCVE-2016-4556Moderate

squid: SIGSEGV in ESIContext response handling

May 6, 2016

References

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