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CVE-2020-15811

6.5
MEDIUMCVSS v3.1 Base Score
4.23%
LOW RiskEPSS (90th percentile)

An issue was discovered in Squid before 4.13 and 5.x before 5.0.4. Due to incorrect data validation, HTTP Request Splitting attacks may succeed against HTTP and HTTPS traffic. This leads to cache poisoning. This allows any client, including browser scripts, to bypass local security and poison the browser cache and any downstream caches with content from an arbitrary source. Squid uses a string search instead of parsing the Transfer-Encoding header to find chunked encoding. This allows an attacker to hide a second request inside Transfer-Encoding: it is interpreted by Squid as chunked and split out into a second request delivered upstream. Squid will then deliver two distinct responses to the client, corrupting any downstream caches.

Published: 9/2/2020
Modified: 6/17/2026
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Vulnerability Summary

CVSS v3 Score

6.5MEDIUM

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N

CVSS v2 Score

4

AV:N/AC:L/Au:S/C:N/I:P/A:N

EPSS Score (Exploitation Probability)

4.23%LOW Exploitation Risk
90th percentile

This vulnerability has a 4.23% probability of being exploited in the next 30 days, ranking higher than 90% of all scored CVEs.

CWE Classification

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Same Weakness Type(CWE-697)

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Similar SeverityMEDIUM