CVE-2016-4553
Highclient_side.cc in Squid before 3.5.18 and 4.x before 4.0.10 does not properly ignore the Host header when absolute-URI is provided, which allows remote attackers to conduct cache-poisoning attacks via an HTTP request.
Published May 6, 2016 · Updated Jul 8, 2026 · Also known as UBUNTU-CVE-2016-4553
Key Facts
Patch immediately- CVE-2016-4553 is a high-severity vulnerability (CVSS 8.6 v3.1) affecting Squid (Squid-Cache), Ubuntu Linux (Canonical), Linux (Oracle) and 3 more products.
- It is not listed in any known-exploited vulnerabilities catalog. No public exploit code is known.
- EPSS estimates a 80% probability of exploitation in the next 30 days.
- Fixed versions are available, including Squid 3.3.14-20.2, Squid 3.3.14-6.1, Squid 4.16-1.5.
- Brandefense priority: patch immediately, because it is very likely to be exploited soon.
CVSS v3.1
8.6
CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:H/A:N
EPSS (30-day exploit likelihood)
80%
Higher than 99.6% of all scored CVEs
Exploited in the wild
No known
Not in a known-exploited catalog
Public exploit code
None known
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Description
client_side.cc in Squid before 3.5.18 and 4.x before 4.0.10 does not properly ignore the Host header when absolute-URI is provided, which allows remote attackers to conduct cache-poisoning attacks via an HTTP request.
Affected Products
38 affected entries in total| Product | Affected versions | Fixed in |
|---|---|---|
| SquidSquid-Cache | 4.0.1, 4.0.2, 4.0.3, 4.0.4, 4.0.5, 4.0.6, 4.0.7, 4.0.8 | 3.5.17 |
| Ubuntu LinuxCanonical | 12.04, 14.04, 15.10, 16.04 | n/a |
| LinuxOracle | 7 | n/a |
| squid3debian | See advisory | 3.4.8-6+deb8u3 |
| squid34oracle | See advisory | 7:3.4.14-9.el6_8.3 |
Patched Releases
Squid
3.3.14-20.2, 3.3.14-6.1, 4.16-1.5, 7:3.3.8-26.el7_2.3, 3.5.17
squid-sysvinit
7:3.3.8-26.el7_2.3
squid3
3.1.23-8.16.30.1, 3.3.8-1ubuntu6.8, 3.4.8-6+deb8u3, 3.5.12-1ubuntu7.2
squid34
7:3.4.14-9.el6_8.3
Timeline
Publicly disclosed
May 6, 2016
Last updated
Jul 8, 2026
Weakness Type
- CWE-20 Improper Input Validation
- CWE-345 Insufficient Verification of Data Authenticity
References
- advisoryhttp://bugs.squid-cache.org/show_bug.cgi?id=4501
- advisoryRHSA-2016:1139
- advisoryRHSA-2016:1140
- advisoryhttps://bugzilla.suse.com/895773
- advisoryhttps://bugzilla.suse.com/902197
FAQ
Common Questions.
client_side.cc in Squid before 3.5.18 and 4.x before 4.0.10 does not properly ignore the Host header when absolute-URI is provided, which allows remote attackers to conduct cache-poisoning attacks via an HTTP request.
Affected: Squid (Squid-Cache) versions 4.0.1, 4.0.2, 4.0.3, 4.0.4, 4.0.5, 4.0.6, 4.0.7, 4.0.8; Ubuntu Linux (Canonical) versions 12.04, 14.04, 15.10, 16.04; Linux (Oracle) versions 7, among others. The full list is in the CVE brief.
It is not listed in any known-exploited vulnerabilities catalog.
No, it is not currently listed in the CISA Known Exploited Vulnerabilities catalog.
No public exploit code is known.
Fixed versions are available, including Squid 3.3.14-20.2, Squid 3.3.14-6.1, Squid 4.16-1.5.
Brandefense priority: patch immediately, because it is very likely to be exploited soon.
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