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Fencer Vulns
medium 6.5

CVE-2020-15811 json

An issue was discovered in Squid before 4.13 and 5.x before 5.0.4.

published 2020-09-02 6 y ago modified 2026-06-17 4 mo ago also EUVD-2020-7794

cvss
6.5
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
3.8%
EPSS 3.8% chance of exploitation in 30 days, percentile 90%
public exploits
0
none known

Summary

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.

Patch / fix

  • squid-cache squid 4.13, 5.0.4
  • squid Debian 14, Debian 13, Debian 12 4.13-1

debian advisories DEBIAN-CVE-2020-15811

  • squid Ubuntu 20.04 LTS 4.10-1ubuntu1.2
  • squid3 Ubuntu 16.04 LTS 3.5.12-1ubuntu7.15
  • squid3 Ubuntu 18.04 LTS 3.5.27-1ubuntu1.9

ubuntu advisories UBUNTU-CVE-2020-15811

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • squid RHEL 7 7:3.5.20-17.el7_9.4
  • squid-sysvinit RHEL 7 7:3.5.20-17.el7_9.4
  • squid-migration-script RHEL 7 7:3.5.20-17.el7_9.4
  • squid RHEL 8 7:4.4-8.module+el8.2.0+7834+b8ecaeef.2
  • libecap RHEL 8.1 EUS, RHEL 8 1.0.1-2.module+el8.1.0+4044+36416a77
  • squid RHEL 8.0 E4S 7:4.4-5.module+el8.0.0+7838+974c4845.2
  • squid RHEL 8.1 EUS 7:4.4-8.module+el8.1.0+7837+e38d3ca0.2
  • libecap RHEL 8.0 E4S 1.0.1-2.module+el8.0.0+4045+70edde92

red hat advisories RHSA-2020:4082RHSA-2020:3623

  • squid3 SLES 11 SP4-LTSS, SLE Point of Sale 11 SP3 3.1.23-8.16.37.15.1
  • squid SLES for SAP 12 SP4, SLES for SAP 12 SP3, SLES for SAP 12 SP2 +12 more 3.5.21-26.32.1
  • squid SLES for SAP 12 SP5, SLES 12 SP5 4.13-4.15.1
  • squid SLES for SAP 15, SLES 15-LTSS, SLE Module for Server Applications 15 SP2 +3 more 4.13-5.23.1

suse advisories SUSE-SU-2020:14590-1SUSE-SU-2020:2471-1SUSE-SU-2020:2443-1SUSE-SU-2020:2442-1

  • squid openSUSE Tumbleweed 4.16-1.5
  • squid openSUSE Leap 15.2 4.13-lp152.2.6.1
  • squid openSUSE Leap 15.1 4.13-lp151.2.24.1

opensuse advisories openSUSE-SU-2024:11403-1openSUSE-SU-2020:1369-1openSUSE-SU-2020:1346-1

  • libecap Rocky Linux 8 1.0.1-2.module+el8.4.0+404+316a0dc5

rocky linux advisories RLSA-2020:3623

  • squid Alpine 3.12, Alpine 3.11, Alpine 3.10 +1 more 4.13-r0
  • squid Alpine 3.24, Alpine 3.23, Alpine 3.22 +9 more 4.13.0-r0

alpine advisories ALPINE-CVE-2020-15811

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2020-15811 updated cvss 9.6

squid: HTTP Request Splitting could result in cache poisoning

  • Red Hat Enterprise Linux 5 squid Red Hat Enterprise Linux 6 squid, squid34
    affected: workaround, no fix planned “Disable the relaxed HTTP parser in `squid.conf`: ``` relaxed_header_parser off ```”
  • Red Hat Enterprise Linux AppStream (v. 8) squid 4.4-8.module+el8.2.0+7834+b8ecaeef.2, libecap 1.0.1-2.module+el8.1.0+4044+36416a77 Red Hat Enterprise Linux AppStream E4S (v. 8.0) squid 4.4-5.module+el8.0.0+7838+974c4845.2, libecap 1.0.1-2.module+el8.0.0+4045+70edde92 Red Hat Enterprise Linux AppStream EUS (v. 8.1) squid 4.4-8.module+el8.1.0+7837+e38d3ca0.2, libecap 1.0.1-2.module+el8.1.0+4044+36416a77
    fixed: vendor fix “Disable the relaxed HTTP parser in `squid.conf`: ``` relaxed_header_parser off ```” RHSA-2020:3623
  • Red Hat Enterprise Linux Server (v. 7) squid 3.5.20-17.el7_9.4, squid-migration-script 3.5.20-17.el7_9.4 Red Hat Enterprise Linux Server Optional (v. 7) squid-sysvinit 3.5.20-17.el7_9.4 Red Hat Enterprise Linux Workstation (v. 7) squid 3.5.20-17.el7_9.4, squid-migration-script 3.5.20-17.el7_9.4 Red Hat Enterprise Linux Workstation Optional (v. 7) squid-sysvinit 3.5.20-17.el7_9.4
    fixed: vendor fix “Disable the relaxed HTTP parser in `squid.conf`: ``` relaxed_header_parser off ```” RHSA-2020:4082

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

3.81% chance of exploitation in the next 30 days, higher than 90% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
NVD 3.1 6.5 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N
NVD 2.0 4.0 AV:N/AC:L/Au:S/C:N/I:P/A:N

Classification

Weakness

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.