How severe is CVE-2016-4554?

CVE-2016-4554 has a CVSS 3.x base score of 8.6, 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 high, and availability none.

Is CVE-2016-4554 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 39% (98th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2016-4554?

CVE-2016-4554 primarily affects Squid-cache Squid. In total, 7 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2016-4554?

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-2016-4554 published?

CVE-2016-4554 was published on 2016-05-10 and last updated on 2026-06-17.

CVE-2016-4554

CVE-2016-4554 is a high-severity vulnerability in Squid-cache Squid with a CVSS 3.x base score of 8.6. Its EPSS exploit-prediction score of 39% places it in the 98th percentile, indicating an elevated likelihood of exploitation. The underlying weakness is classified as CWE-345.

Key facts

Severity: High (CVSS 3.x base score 8.6)
CVSS v2: 5.0
EPSS exploit prediction: 39% (98th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-345
Affected product: Squid-cache Squid
Published: 2016-05-10
Last modified: 2026-06-17

Description

mime_header.cc in Squid before 3.5.18 allows remote attackers to bypass intended same-origin restrictions and possibly conduct cache-poisoning attacks via a crafted HTTP Host header, aka a "header smuggling" issue.

Frequently asked questions

What is CVE-2016-4554?: mime_header.cc in Squid before 3.5.18 allows remote attackers to bypass intended same-origin restrictions and possibly conduct cache-poisoning attacks via a crafted HTTP Host header, aka a "header smuggling" issue.
How severe is CVE-2016-4554?: CVE-2016-4554 has a CVSS 3.x base score of 8.6, 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 high, and availability none.
Is CVE-2016-4554 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 39% (98th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2016-4554?: CVE-2016-4554 primarily affects Squid-cache Squid. In total, 7 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2016-4554?: 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-2016-4554 published?: CVE-2016-4554 was published on 2016-05-10 and last updated on 2026-06-17.

References

Affected products (7)

cpe:2.3:o:oracle:linux:6:*:*:*:*:*:*:*
cpe:2.3:o:oracle:linux:7:*:*:*:*:*:*:*
cpe:2.3:a:squid-cache:squid:*:*:*:*:*:*:*:*
cpe:2.3:o:canonical:ubuntu_linux:12.04:*:*:*:lts:*:*:*
cpe:2.3:o:canonical:ubuntu_linux:14.04:*:*:*:lts:*:*:*
cpe:2.3:o:canonical:ubuntu_linux:15.10:*:*:*:*:*:*:*
cpe:2.3:o:canonical:ubuntu_linux:16.04:*:*:*:lts:*:*:*

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Threat intelligence

Threat-intel indicators referencing this CVE:

200.89.159.59 (ipv4-addr)