PatchTheCVECVE-2020-11653: An issue was discovered in Varnish Cache before 6.0.6 LTS, 6.1.x and 6.2.x before 6.2.3, and 6.3.x before 6.3.
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HIGH 7.5REMOTEWATCHLISTUPGRADEUPGRADEDOWNGRADE
CVE-2020-11653 is a high-severity flaw (CVSS 7.5) affecting varnish cache, varnish cache, backports sle. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.
An issue was discovered in Varnish Cache before 6.0.6 LTS, 6.1.x and 6.2.x before 6.2.3, and 6.3.x before 6.3.2. It occurs when communication with a TLS termination proxy uses PROXY version 2. There can be an assertion failure and daemon restart, which causes a performance loss.
Why this priority
- High severity
- Remotely exploitable, no login, no user action
- On your watchlist
A fixed release or distro patch exists.
Risk facts
| CVSS score | 7.5 (High) |
| Attack vector | Network (remote) |
| Attack complexity | Low |
| Privileges needed | None |
| User interaction | None |
| EPSS exploit chance | 2.2% (top 18%) |
| CISA exploited list | No |
| Weakness | CWE-617 |
| Published | 2020-04-08 |
| Last modified | 2026-06-17 |
Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score
Am I affected?
Timeline
- Published CVE record published
- Updated Record last modified
varnish-cache varnish cache UPGRADE
Affected: >= 6.1.0 and < 6.2.3 · >= 6.3.0 and < 6.3.2
Fixed in: 6.2.3, 6.3.2
Safe to downgrade to: a release before 6.1.0
1. Check installed version
apt-cache policy varnish-cache || rpm -q varnish-cache || varnish-cache --version
2. UPGRADE to 6.2.3 (Debian / Ubuntu)
sudo apt update && sudo apt install --only-upgrade varnish-cache
2. UPGRADE (RHEL / Amazon Linux / Fedora)
sudo dnf upgrade varnish-cache
Note
Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.
3. If no update is available yet, DOWNGRADE to a release before 6.1.0 (Debian / Ubuntu)
apt-cache madison varnish-cache
sudo apt install varnish-cache=<VERSION_BEFORE_6.1.0>
sudo apt-mark hold varnish-cache
3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)
dnf --showduplicates list varnish-cache
sudo dnf downgrade varnish-cache-<VERSION_BEFORE_6.1.0>
sudo dnf versionlock add varnish-cache
Downgrade risk
Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.
After downgrade
Restart the service, and keep the package held until a fixed release ships.
varnish-software varnish cache UPGRADE
Affected: >= 6.0.0 and < 6.0.6
Fixed in: 6.0.6
Safe to downgrade to: a release before 6.0.0
1. Check installed version
apt-cache policy varnish-cache || rpm -q varnish-cache || varnish-cache --version
2. UPGRADE to 6.0.6 (Debian / Ubuntu)
sudo apt update && sudo apt install --only-upgrade varnish-cache
2. UPGRADE (RHEL / Amazon Linux / Fedora)
sudo dnf upgrade varnish-cache
Note
Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.
3. If no update is available yet, DOWNGRADE to a release before 6.0.0 (Debian / Ubuntu)
apt-cache madison varnish-cache
sudo apt install varnish-cache=<VERSION_BEFORE_6.0.0>
sudo apt-mark hold varnish-cache
3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)
dnf --showduplicates list varnish-cache
sudo dnf downgrade varnish-cache-<VERSION_BEFORE_6.0.0>
sudo dnf versionlock add varnish-cache
Downgrade risk
Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.
After downgrade
Restart the service, and keep the package held until a fixed release ships.
opensuse backports sle DOWNGRADE
Affected: 15.0 sp1
Fixed in: no fixed release known
Safe to downgrade to: a release before 15.0
1. Check installed version
apt-cache policy backports-sle || rpm -q backports-sle || backports-sle --version
2. No fixed release: DOWNGRADE to a release before 15.0 (Debian / Ubuntu)
apt-cache madison backports-sle
sudo apt install backports-sle=<VERSION_BEFORE_15.0>
sudo apt-mark hold backports-sle
2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)
dnf --showduplicates list backports-sle
sudo dnf downgrade backports-sle-<VERSION_BEFORE_15.0>
sudo dnf versionlock add backports-sle
Downgrade risk
Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.
After downgrade
Restart the service, and keep the package held until a fixed release ships.
opensuse leap MITIGATE
Affected: 15.1
Fixed in: no fixed release known
Safe to downgrade to: a release before 15.1
Check your OS release
cat /etc/os-release; uname -r
Debian / Ubuntu
sudo apt update && sudo apt full-upgrade
RHEL / Amazon Linux / Fedora
sudo dnf upgrade --refresh
Windows
Install the latest cumulative update from Windows Update
If no patch exists yet
OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.
debian debian linux MITIGATE
Affected: 10.0
Fixed in: no fixed release known
Safe to downgrade to: a release before 10.0
Check your OS release
cat /etc/os-release; uname -r
Debian / Ubuntu
sudo apt update && sudo apt full-upgrade
RHEL / Amazon Linux / Fedora
sudo dnf upgrade --refresh
Windows
Install the latest cumulative update from Windows Update
If no patch exists yet
OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.
Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.
Quick answers
How do I fix CVE-2020-11653?
varnish cache: upgrade to 6.2.3, 6.3.2; varnish cache: upgrade to 6.0.6; backports sle: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.
Is CVE-2020-11653 being exploited?
CVE-2020-11653 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.
What does CVE-2020-11653 affect?
CVE-2020-11653 affects varnish cache, varnish cache, backports sle. Severity is high (CVSS 7.5). An issue was discovered in Varnish Cache before 6.0.6 LTS, 6.1.x and 6.2.x before 6.2.3, and 6.3.x before 6.3.2. It occurs when communication with a TLS termination proxy uses PROXY version 2. There can be an assertion failure and daemon re
How urgent is CVE-2020-11653?
Priority 57/100. High severity; Remotely exploitable, no login, no user action; On your watchlist
Software pages
Debian vulnerabilities · Varnish vulnerabilities
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