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Fencer Intel
high 7.5

CVE-2016-4556 in the critical feed json

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 (cr…

published 2016-05-10 10 y ago modified 2026-06-17 4 mo ago also EUVD-2016-5543

cvss
7.5
version 3.0, NVD
cisa kev
Not listed
not in CISA's catalog
epss
23.1%
EPSS 23.1% chance of exploitation in 30 days, percentile 97%
public exploits
0
none known

Summary

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.

Patch / fix

  • squid3 Ubuntu 14.04 LTS 3.3.8-1ubuntu6.8
  • squid3 Ubuntu 16.04 LTS 3.5.12-1ubuntu7.2

ubuntu advisories UBUNTU-CVE-2016-4556

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • squid RHEL 7 7:3.3.8-26.el7_2.3
  • squid-sysvinit RHEL 7 7:3.3.8-26.el7_2.3
  • squid34 RHEL 6 7:3.4.14-9.el6_8.3
  • squid RHEL 6 7:3.1.23-16.el6_8.4

red hat advisories RHSA-2016:1139RHSA-2016:1140RHSA-2016:1138

  • squid3 SLES for SAP 11 SP4, SLES 11 SP4 3.1.23-8.16.30.1
  • squid SLES for SAP 12 SP1, SLES 12 SP1 3.3.14-20.2

suse advisories SUSE-SU-2016:2089-1SUSE-SU-2016:2008-1

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2016-4556 updated cvss 4.3

squid: SIGSEGV in ESIContext response handling

  • Red Hat Enterprise Linux Server (v. 6) squid 3.1.23-16.el6_8.4, squid34 3.4.14-9.el6_8.3
    fixed: vendor fix RHSA-2016:1138
  • Red Hat Enterprise Linux Server (v. 7) squid 3.3.8-26.el7_2.3 Red Hat Enterprise Linux Server Optional (v. 7) squid-sysvinit 3.3.8-26.el7_2.3
    fixed: vendor fix RHSA-2016:1139
  • Red Hat Enterprise Linux Workstation (v. 6) squid 3.1.23-16.el6_8.4, squid34 3.4.14-9.el6_8.3
    fixed: vendor fix RHSA-2016:1138
  • Red Hat Enterprise Linux Workstation (v. 7) squid 3.3.8-26.el7_2.3 Red Hat Enterprise Linux Workstation Optional (v. 7) squid-sysvinit 3.3.8-26.el7_2.3
    fixed: vendor fix RHSA-2016:1139
  • Red Hat Enterprise Linux 5 squid
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

23.11% chance of exploitation in the next 30 days, higher than 97% of all scored CVEs (FIRST EPSS, 2026-11-09).

CVSS scores

assigned by version score vector
NVD 3.0 7.5 CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
NVD 2.0 5.0 AV:N/AC:L/Au:N/C:N/I:N/A:P

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.