How severe is CVE-2016-4555?

CVE-2016-4555 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-2016-4555 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 54% (99th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2016-4555?

CVE-2016-4555 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-2016-4555?

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-2016-4555 published?

CVE-2016-4555 was published on 2016-05-10 and last updated on 2026-06-17.

CVE-2016-4555

CVE-2016-4555 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 54% places it in the 99th percentile, indicating an elevated likelihood of exploitation. The underlying weakness is classified as CWE-20.

Key facts

Severity: High (CVSS 3.x base score 7.5)
CVSS v2: 5.0
EPSS exploit prediction: 54% (99th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-20
Affected product: Squid-cache Squid
Published: 2016-05-10
Last modified: 2026-06-17

Description

client_side_request.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 crafted Edge Side Includes (ESI) responses.

Frequently asked questions

What is CVE-2016-4555?: client_side_request.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 crafted Edge Side Includes (ESI) responses.
How severe is CVE-2016-4555?: CVE-2016-4555 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-2016-4555 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 54% (99th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2016-4555?: CVE-2016-4555 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-2016-4555?: 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-2016-4555 published?: CVE-2016-4555 was published on 2016-05-10 and last updated on 2026-06-17.

References

Affected products (148)

cpe:2.3:a:squid-cache:squid:3.0:*:*:*:*:*:*:*
cpe:2.3:a:squid-cache:squid:3.1:*:*:*:*:*:*:*
cpe:2.3:a:squid-cache:squid:3.1.0.1:*:*:*:*:*:*:*
cpe:2.3:a:squid-cache:squid:3.1.0.2:*:*:*:*:*:*:*
cpe:2.3:a:squid-cache:squid:3.1.0.3:*:*:*:*:*:*:*
cpe:2.3:a:squid-cache:squid:3.1.0.4:*:*:*:*:*:*:*
cpe:2.3:a:squid-cache:squid:3.1.0.5:*:*:*:*:*:*:*
cpe:2.3:a:squid-cache:squid:3.1.0.6:*:*:*:*:*:*:*
cpe:2.3:a:squid-cache:squid:3.1.0.7:*:*:*:*:*:*:*
cpe:2.3:a:squid-cache:squid:3.1.0.8:*:*:*:*:*:*:*
cpe:2.3:a:squid-cache:squid:3.1.0.9:*:*:*:*:*:*:*
cpe:2.3:a:squid-cache:squid:3.1.0.10:*:*:*:*:*:*:*
cpe:2.3:a:squid-cache:squid:3.1.0.11:*:*:*:*:*:*:*
cpe:2.3:a:squid-cache:squid:3.1.0.12:*:*:*:*:*:*:*
cpe:2.3:a:squid-cache:squid:3.1.0.13:*:*:*:*:*:*:*
cpe:2.3:a:squid-cache:squid:3.1.0.14:*:*:*:*:*:*:*
cpe:2.3:a:squid-cache:squid:3.1.0.15:*:*:*:*:*:*:*
cpe:2.3:a:squid-cache:squid:3.1.0.16:*:*:*:*:*:*:*
cpe:2.3:a:squid-cache:squid:3.1.0.17:*:*:*:*:*:*:*
cpe:2.3:a:squid-cache:squid:3.1.0.18:*:*:*:*:*:*:*
cpe:2.3:a:squid-cache:squid:3.1.1:*:*:*:*:*:*:*
cpe:2.3:a:squid-cache:squid:3.1.2:*:*:*:*:*:*:*
cpe:2.3:a:squid-cache:squid:3.1.3:*:*:*:*:*:*:*
cpe:2.3:a:squid-cache:squid:3.1.4:*:*:*:*:*:*:*
cpe:2.3:a:squid-cache:squid:3.1.5:*:*:*:*:*:*:*
cpe:2.3:a:squid-cache:squid:3.1.5.1:*:*:*:*:*:*:*
cpe:2.3:a:squid-cache:squid:3.1.6:*:*:*:*:*:*:*
cpe:2.3:a:squid-cache:squid:3.1.7:*:*:*:*:*:*:*
cpe:2.3:a:squid-cache:squid:3.1.8:*:*:*:*:*:*:*
cpe:2.3:a:squid-cache:squid:3.1.9:*:*:*:*:*:*:*
cpe:2.3:a:squid-cache:squid:3.1.10:*:*:*:*:*:*:*
cpe:2.3:a:squid-cache:squid:3.1.11:*:*:*:*:*:*:*
cpe:2.3:a:squid-cache:squid:3.1.12:*:*:*:*:*:*:*
cpe:2.3:a:squid-cache:squid:3.1.12.1:*:*:*:*:*:*:*
cpe:2.3:a:squid-cache:squid:3.1.12.2:*:*:*:*:*:*:*
cpe:2.3:a:squid-cache:squid:3.1.12.3:*:*:*:*:*:*:*
cpe:2.3:a:squid-cache:squid:3.1.13:*:*:*:*:*:*:*
cpe:2.3:a:squid-cache:squid:3.1.14:*:*:*:*:*:*:*
cpe:2.3:a:squid-cache:squid:3.1.15:*:*:*:*:*:*:*
cpe:2.3:a:squid-cache:squid:3.1.16:*:*:*:*:*:*:*

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Threat intelligence

Threat-intel indicators referencing this CVE:

193.90.12.40 (ipv4-addr)
200.89.159.59 (ipv4-addr)