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Fencer Intel
medium 6.5

CVE-2021-36740 json

Varnish Cache, with HTTP/2 enabled, allows request smuggling and VCL authorization bypass via a large Content-Length header for a POST requ…

published 5y ago modified 2mo ago also BIT-varnish-2021-36740 , EUVD-2021-23330

cvss
6.5
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
1.6%
EPSS 1.6% chance of exploitation in 30 days, percentile 75%
public exploits
0
none known

Summary

Varnish Cache, with HTTP/2 enabled, allows request smuggling and VCL authorization bypass via a large Content-Length header for a POST request. This affects Varnish Enterprise 6.0.x before 6.0.8r3, and Varnish Cache 5.x and 6.x before 6.5.2, 6.6.x before 6.6.1, and 6.0 LTS before 6.0.8.

Patch / fix

  • bitnami varnish 5.2.2, 6.6.1
  • varnish-cache varnish_cache 6.0.8
  • varnish Debian 13, Debian 12 6.5.2-1

debian advisories DEBIAN-CVE-2021-36740

  • varnish Ubuntu 20.04 LTS 6.2.1-2ubuntu0.1

ubuntu advisories UBUNTU-CVE-2021-36740

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

  • rh-varnish6-varnish RHEL 3 SOFTWARE_COLLECTIONS 6.0.8-2.el7
  • rh-varnish6-varnish-libs RHEL 3 SOFTWARE_COLLECTIONS 6.0.8-2.el7
  • rh-varnish6-varnish-modules RHEL 3 SOFTWARE_COLLECTIONS 0.15.0-7.el7
  • varnish RHEL 8 6.0.6-2.module+el8.4.0+11921+1a6539fc.1
  • varnish-modules RHEL 8 0.15.0-5.module+el8.3.0+6843+b3b42fcc
  • varnish RHEL 8.1 EUS 6.0.2-2.module+el8.1.0+11974+ea5ba4f1
  • varnish RHEL 8.2 EUS 6.0.2-2.module+el8.2.0+11973+a748eca7
  • varnish-modules RHEL 8.2 EUS, RHEL 8.1 EUS 0.15.0-4.module+el8+2481+4078e9d2

red hat advisories RHSA-2021:2993RHSA-2021:2988

  • varnish Package Hub 15 SP3, openSUSE Leap 15.3 7.1.0-bp153.2.3.1

opensuse advisories openSUSE-SU-2022:0148-1

  • varnish Rocky Linux 8 6.0.6-2.module+el8.3.0+179+20b582cc
  • varnish-modules Rocky Linux 8 0.15.0-5.module+el8.3.0+179+20b582cc

rocky linux advisories RLSA-2021:2988

  • varnish Alpine 3.13, Alpine 3.12, Alpine 3.11 6.5.2-r0
  • varnish Alpine 3.24, Alpine 3.23, Alpine 3.22 +8 more 6.6.1-r0

alpine advisories ALPINE-CVE-2021-36740

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

Is CVE-2021-36740 in your dependencies? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.

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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-2021-36740 updated cvss 8.1

varnish: HTTP/2 request smuggling attack via a large Content-Length header for a POST request

  • Red Hat Enterprise Linux AppStream (v. 8) varnish 6.0.6-2.module+el8.4.0+11921+1a6539fc.1, varnish-modules 0.15.0-5.module+el8.3.0+6843+b3b42fcc Red Hat Enterprise Linux AppStream EUS (v. 8.1) varnish 6.0.2-2.module+el8.1.0+11974+ea5ba4f1, varnish-modules 0.15.0-4.module+el8+2481+4078e9d2 Red Hat Enterprise Linux AppStream EUS (v. 8.2) varnish 6.0.2-2.module+el8.2.0+11973+a748eca7, varnish-modules 0.15.0-4.module+el8+2481+4078e9d2
    fixed: vendor fix RHSA-2021:2988
  • Red Hat Software Collections for Red Hat Enterprise Linux Server (v. 7) rh-varnish6-varnish 6.0.8-2.el7, rh-varnish6-varnish-libs 6.0.8-2.el7, rh-varnish6-varnish-modules 0.15.0-7.el7 Red Hat Software Collections for Red Hat Enterprise Linux Server EUS (v. 7.7) rh-varnish6-varnish 6.0.8-2.el7, rh-varnish6-varnish-libs 6.0.8-2.el7, rh-varnish6-varnish-modules 0.15.0-7.el7 Red Hat Software Collections for Red Hat Enterprise Linux Workstation (v. 7) rh-varnish6-varnish 6.0.8-2.el7, rh-varnish6-varnish-libs 6.0.8-2.el7, rh-varnish6-varnish-modules 0.15.0-7.el7
    fixed: vendor fix RHSA-2021:2993
  • Red Hat Enterprise Linux 9 varnish
    not affected: vulnerable code not present

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

1.60% chance of exploitation in the next 30 days, higher than 75% of all scored CVEs (FIRST EPSS, 2026-11-09).

CVSS scores

assigned by version score vector
NVD 3.1 6.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
NVD 2.0 6.4 AV:N/AC:L/Au:N/C:P/I:P/A:N
OSV 3.1 6.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N

Affected packages

ecosystem package affected fixed in
bitnami varnish
>=5.0.0, <5.2.2
>=6.1.0, <6.6.1
5.2.2
6.6.1

Classification

Weakness
  • CWE-444 Inconsistent Interpretation of HTTP Requests

References

Sources

Fencer Intel 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.