CVE-2016-4556

CVE-2016-4556 is a high-severity vulnerability in Squid-cache Squid with a CVSS 3.x base score of 7.5. Its EPSS exploit-prediction score of 23% places it in the 97th percentile, indicating an elevated likelihood of exploitation.

Key facts

Description

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.

Frequently asked questions

What is 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.
How severe is CVE-2016-4556?
CVE-2016-4556 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2016-4556 being actively exploited?
It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 23% (97th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2016-4556?
CVE-2016-4556 primarily affects Squid-cache Squid. In total, 148 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2016-4556?
Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2016-4556 published?
CVE-2016-4556 was published on 2016-05-10 and last updated on 2026-06-17.

References

Affected products (148)

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Threat intelligence

Threat-intel indicators referencing this CVE: