CVE-2020-15811

CVE-2020-15811 is a medium-severity vulnerability in Squid-cache Squid with a CVSS 3.x base score of 6.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-697.

Key facts

Description

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.

Frequently asked questions

What is CVE-2020-15811?
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.
How severe is CVE-2020-15811?
CVE-2020-15811 has a CVSS 3.x base score of 6.5, rated medium severity. It is exploitable over network with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is none, integrity high, and availability none.
Is CVE-2020-15811 being actively exploited?
It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 4% (90th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2020-15811?
CVE-2020-15811 primarily affects Squid-cache Squid. In total, 11 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2020-15811?
Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2020-15811 published?
CVE-2020-15811 was published on 2020-09-02 and last updated on 2026-06-17.

References

Affected products (11)

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Threat intelligence

Threat-intel indicators referencing this CVE: