No exploitation reportedFix available

CVE-2021-36740

No exploitation reported by the sources we read.

Published2021-07-14
WeaknessCWE-444

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

Description

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.

Timeline

dates in UTC

2021-07-1417:15CVE publishedNVD

Observed activity

isMalicious corpus · updated 2026-10-23 21:37 UTC

Indicators tagged with this CVE, per day0 indicators over 7 days

Block these indicators

Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2021-36740?format=txt
CSV export: https://api.ismalicious.com/edl/cve/CVE-2021-36740?format=csv
TAXII collection of exploited CVEs
The EDL and CSV take an API key on the Pro plan.

Versions per branch

NVD

Debian debian linux

Branch	Affected	Fixed in	Source
10.0	= 10.0	no fix published	NVD
11.0	= 11.0	no fix published	NVD

Fedoraproject fedora

Branch	Affected	Fixed in	Source
33.x	= 33	no fix published	NVD
34.x	= 34	no fix published	NVD

Varnish cache project varnish cache

Branch	Affected	Fixed in	Source
5.x	≥ 5.0.0, ≤ 5.2.1	no fix published	NVD
6.x	≥ 6.1.0, ≤ 6.6.0	no fix published	NVD

3 more products in the sources.

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Fix

Advisories and patches

docs.varnish-software.comMitigation · Vendor Advisory
github.comPatch
github.comPatch
varnish-cache.orgMitigation · Vendor Advisory

Detection

Nuclei template: none so far
Exploit-DB: no entry
Proof-of-concept repositories: none listed

Sources

NVDCVSS 3.16.5read 2026-10-23
NVDCVSS 2.06.4read 2026-10-23
NVDweakness (CWE)CWE-444read 2026-10-23
FIRST EPSSEPSS score1.6 %2026-10-23
OSVaffected packages—

Technical details

CVSS v3 Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
Published: 2021-07-14
Last Modified: 2026-06-17
NVD status: Modified

Frequently asked questions

What is CVE-2021-36740?

Is CVE-2021-36740 actively exploited?

Active exploitation of CVE-2021-36740 has not been confirmed. Its EPSS score was 1.6% on 2026-10-23, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2021-36740?

CVE-2021-36740 has a CVSS v3 base score of 6.5 (MEDIUM severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N.

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